MarkdownToNotebook.wl

(* MarkdownToNotebook - convert a literate-markdown document into a Wolfram
   notebook, choosing the layout from a template.

   The source can be a local file path, an http(s) URL, or a raw markdown
   string. The Template frontmatter key selects a registry entry:
     FunctionResource - fill the slots of the official Function Repository
        definition template (its stylesheet and docked Deploy/Submit toolbar
        are preserved), so the .nb is publishable as-is.
     Symbol, Guide - fill the DocumentationTools authoring templates.
     Default - map headings and code directly to standard notebook styles.
   Frontmatter drives metadata; the Definition section is the code; example
   sections become evaluated + cached Input/Output cells.

   Deliberately plain top-level definitions (no BeginPackage): the converter
   Gets this file into a freshly generated private context so converting a
   document cannot clobber the live definition doing the converting. *)

Needs["GeneralUtilities`"]

(* The LaTeX math pipeline wants the published Wolfram/Parser paclet - its
   LaTeXMathParse handles \frac / \mathbb / scripts / sized delimiters that
   the ImportString[..., "TeX"] fallback (wolframParserTeX) loses.

   The dependency is enforced on USE (ensureParser[], called by every
   MarkdownToNotebook invocation), not at load. A deployed ResourceFunction's
   body is loaded once in whatever session first dereferences it (the build /
   deploy kernel), so the check + Needs must run when the function is actually
   called, in the caller's kernel - the same reason $convertDepth is read at
   call time below. Only the vendored-submodule path is resolved here, while
   $InputFileName still points at this file. *)
(* the vendored submodule, resolved against THIS file's location so it is found
   from any working directory - the old cwd-relative check silently degraded to
   ImportString when MTN ran from elsewhere (issue #25) *)
$parserDir = FileNameJoin[{
    Replace[DirectoryName[$InputFileName], "" :> Directory[]], "examples", "Paclet", "WolframParser"}]
$parserReady = False
(* Make Wolfram`Parser` available, once per session. Prefer the vendored submodule
   (PacletDirectoryLoad makes the paclet manager serve the highest version, so a
   stale installed copy can't shadow it); else install the published paclet from
   the Paclet Repository (PacletInstall is a no-op when it is already installed).
   Best-effort: if no parser is reachable the math path falls back to ImportString
   (see wolframParserTeX, which gates on the symbol existing at call time rather
   than on this succeeding). *)
ensureParser[] := If[! TrueQ[$parserReady],
    If[ DirectoryQ[$parserDir],
        PacletDirectoryLoad[$parserDir],
        Quiet @ PacletInstall["Wolfram/Parser"]
    ];
    Quiet @ Check[Needs["Wolfram`Parser`"], Null];
    $parserReady = True
]

mdSep = "\n(*--cell--*)\n"

(* === frontmatter === *)

stripQuotes[s_String] := StringReplace[StringTrim[s], {
    StartOfString ~~ "\"" ~~ v___ ~~ "\"" ~~ EndOfString :> v,
    StartOfString ~~ "'" ~~ v___ ~~ "'" ~~ EndOfString :> v
}]

(* split a bracketed list body on commas that are not inside double quotes, so a
   quoted item (e.g. a citation) keeps its internal commas *)
splitListItems[s_String] := Block[{acc = {}, cur = "", inQ = False},
    Do[
        Which[
            c === "\"", inQ = ! inQ; cur = cur <> c,
            c === "," && ! inQ, AppendTo[acc, cur]; cur = "",
            True, cur = cur <> c
        ],
        {c, Characters[s]}
    ];
    Append[acc, cur]
]

parseFmValue[s_String] := Block[{t = StringTrim[s]},
    Which[
        StringMatchQ[t, "[" ~~ ___ ~~ "]"],
            stripQuotes /@ Select[StringTrim /@ splitListItems[StringTake[t, {2, -2}]], # =!= "" &]
        ,
        MemberQ[{"true", "false"}, ToLowerCase[t]],
            ToLowerCase[t] === "true"
        ,
        True,
            stripQuotes[t]
    ]
]

yamlLine[line_String] := Block[{parts = StringSplit[line, ":", 2]},
    StringTrim[First[parts]] -> parseFmValue[Last[parts]]
]

(* A frontmatter list written in flow style, key: ["a", "b", ...], may WRAP across
   several physical lines (long Links: / Authors: lists routinely do). The line-oriented
   parse below would then read only the opening line - an unterminated "[...", which fails
   the [___] list test and collapses to a truncated scalar - and treat each continuation
   line as its own key:value (URLs contain ":", so they parse as garbage keys). Fold those
   continuations back first: accumulate lines while an unquoted "[" is still open and break
   a logical line only once the flow list closes. Brackets INSIDE "..." are literal (markdown
   link labels are full of them), so quoted spans are skipped when tracking depth. *)
foldFrontmatterLines[lines_List] := Block[{out = {}, buf = "", depth = 0, inQ = False},
    Scan[
        Function[line,
            Do[
                Which[
                    c === "\"", inQ = ! inQ,
                    ! inQ && c === "[", depth++,
                    ! inQ && c === "]", depth--
                ],
                {c, Characters[line]}
            ];
            buf = If[buf === "", line, buf <> " " <> line];
            If[depth <= 0, AppendTo[out, buf]; buf = ""; depth = 0]
        ],
        lines
    ];
    If[buf =!= "", AppendTo[out, buf]];
    out
]

parseYamlish[lines_List] := Association @ Map[yamlLine, Select[foldFrontmatterLines[lines], StringContainsQ[#, ":"] &]]

extractFrontmatter[text_String] := Block[{lines, close},
    lines = StringSplit[text, "\n"];
    If[ lines === {} || StringTrim[First[lines]] =!= "---",
        Return[{<||>, text}]
    ];
    close = SelectFirst[Range[2, Length[lines]], StringTrim[lines[[#]]] === "---" &, 0];
    If[ close === 0,
        Return[{<||>, text}]
    ];
    {parseYamlish[lines[[2 ;; close - 1]]], StringRiffle[lines[[close + 1 ;;]], "\n"]}
]

(* === block parsing === *)

fenceQ[line_String] := StringMatchQ[StringTrim[line], "```" ~~ ___]
fenceLen[line_String] := StringLength @ FirstCase[
    StringCases[StringTrim[line], StartOfString ~~ f : ("`" ..) :> f], _String, ""]

headingQ[line_String] := StringMatchQ[line, ("#" ..) ~~ " " ~~ ___]

headingBlock[line_String] := Block[{hashes},
    hashes = First @ StringCases[StringTrim[line], StartOfString ~~ h : ("#" ..) :> h];
    <|
        "Type" -> "Heading",
        "Level" -> StringLength[hashes],
        "Text" -> StringTrim @ StringReplace[StringTrim[line], StartOfString ~~ ("#" ..) ~~ " " -> ""]
    |>
]

parseOptionValue[s_String] := Which[
    MemberQ[{"true", "yes"}, ToLowerCase[StringTrim[s]]], True,
    MemberQ[{"false", "no"}, ToLowerCase[StringTrim[s]]], False,
    True, stripQuotes[s]
]

cellOptionLine[line_String] := Block[{parts = StringSplit[StringReplace[StringTrim[line], StartOfString ~~ "#|" -> ""], ":", 2]},
    StringTrim[First[parts]] -> parseOptionValue[Last[parts]]
]

parseCellOptions[lines_List] := Association @ Map[cellOptionLine, Select[lines, StringContainsQ[#, ":"] &]]

(* a top-level "#| key: value" line - written inline, or recovered by
   stripComments from a "<!-- #| ... -->" metadata comment - is a cell directive
   that binds to the NEXT block (see attachDirectives). Inside a fenced code
   block #| lines are the code cell's own options and are handled by codeBlock. *)
directiveLineQ[line_String] := StringStartsQ[StringTrim[line], "#|"]

codeBlock[info_String, bodyLines_List] := Block[{optLines, codeLines},
    optLines = TakeWhile[bodyLines, StringMatchQ[StringTrim[#], "#|" ~~ ___] &];
    codeLines = Drop[bodyLines, Length[optLines]];
    <|
        "Type" -> "Code",
        "Lang" -> First[StringSplit[ToLowerCase @ StringDelete[info, {"{", "}"}]], ""],
        "Options" -> parseCellOptions[optLines],
        "Code" -> StringRiffle[codeLines, "\n"]
    |>
]

(* fenceSplit[lines, openLen]: gather lines until a CLOSE fence whose own
   backtick run is at least openLen long. A shorter fence inside a longer one
   is content, not a closer (CommonMark semantics). Iterative so we don't
   trip $IterationLimit on a very long inlined-file cell (a `#| file:`
   include of, say, 5000 lines). *)
fenceSplit[lines_List, openLen_Integer] := Module[{n = Length[lines], i = 1},
    While[i <= n && ! (fenceQ[lines[[i]]] && fenceLen[lines[[i]]] >= openLen), i++];
    {Take[lines, i - 1], If[i > n, {}, Drop[lines, i]]}
]

(* Pandoc-style fenced divs ":::". An opening line "::: kind" (kind is any
   non-empty token, e.g. "solved-example", "theorem", "proof", "exercise",
   "solution") starts a div; the matching "::: " closes it. Divs nest.
   Used by the Chapter template to scaffold the multi-cell book constructs
   (SolvedExample, Theorem/Proof, Exercise/Solution) that have no direct
   markdown analogue. *)
divOpenQ[line_String] := Block[{t = StringTrim[line]},
    StringStartsQ[t, ":::"] && StringTrim[StringDrop[t, 3]] =!= ""
]
divCloseQ[line_String] := StringTrim[line] === ":::"
divKind[line_String] := StringTrim[StringDrop[StringTrim[line], 3]]

(* gather lines until the matching ::: closer; respects nested divs *)
divSplit[lines_List] := Block[{depth = 1, acc = {}, rest = lines},
    While[depth > 0 && rest =!= {},
        Which[
            divOpenQ[First[rest]],
                depth++; AppendTo[acc, First[rest]]; rest = Rest[rest],
            divCloseQ[First[rest]],
                depth--;
                If[depth > 0, AppendTo[acc, First[rest]]];
                rest = Rest[rest],
            True,
                AppendTo[acc, First[rest]]; rest = Rest[rest]
        ]
    ];
    {acc, rest}
]

paraSplit[{}, collected_] := {Reverse[collected], {}}
paraSplit[lines_List, collected_] := Block[{line = First[lines]},
    If[ StringTrim[line] === "" || fenceQ[line] || headingQ[line] || listItemQ[line] ||
            orderedItemQ[line] || blockquoteQ[line] || mathBlockOpenQ[line] ||
            divOpenQ[line] || divCloseQ[line],
        {Reverse[collected], lines},
        paraSplit[Rest[lines], Prepend[collected, line]]
    ]
]

(* markdown list items: "- ", "* " or "+ " (the marker is stripped). Tested by
   explicit character checks, not a string pattern: a bare "*" in a
   StringExpression is the wildcard metacharacter, not a literal asterisk. *)
listItemQ[line_String] := Block[{t = StringTrim[line]},
    StringLength[t] >= 2 && MemberQ[{"-", "*", "+"}, StringTake[t, 1]] && StringTake[t, {2}] === " "
]

listText[line_String] := taskCheckbox @ StringTrim @ StringDrop[StringTrim[line], 2]

(* leading-whitespace width of a list line, tabs counted as 4 columns. Used to
   recover the nesting depth of an indented sub-bullet, which listItemQ/listText
   otherwise discard by trimming. *)
listLineIndent[line_String] := Module[
    {m = StringCases[line, StartOfString ~~ w : (" " | "\t") .. :> w, 1]},
    If[m === {}, 0, StringLength[StringReplace[First[m], "\t" -> "    "]]]
]

(* map each item's raw indent width to a 0-based nesting depth. A stack of the
   indent columns seen along the current branch turns *any* indent increase into
   exactly one deeper level (CommonMark nests by alignment, not by a fixed step),
   so both 2- and 4-space sub-bullets nest, and an outdent pops back to the
   matching ancestor level. *)
listDepths[indents_List] := Module[{stack = {}, out = {}},
    Do[
        While[stack =!= {} && Last[stack] > ind, stack = Most[stack]];
        If[stack === {} || Last[stack] < ind, AppendTo[stack, ind]];
        AppendTo[out, Length[stack] - 1],
        {ind, indents}
    ];
    out
]

(* a GitHub task-list item "[ ] ..." / "[x] ..." -> a ballot-box glyph before the
   text (unchecked U+2610, checked U+2611), so the checkbox renders instead of a
   literal "[ ]". *)
taskCheckbox[t_String] := Which[
    StringStartsQ[t, "[ ] "], "\:2610 " <> StringDrop[t, 4],
    StringStartsQ[t, "[x] " | "[X] "], "\:2611 " <> StringDrop[t, 4],
    True, t
]

(* ordered list items: "1. ", "2) ", ... (a run of digits, then "." or ")", then a
   space). The marker is dropped; the List block is tagged "Ordered" so it renders
   numbered. *)
orderedItemQ[line_String] := StringMatchQ[StringTrim[line], DigitCharacter .. ~~ ("." | ")") ~~ " " ~~ ___]
orderedText[line_String] := StringTrim @ StringReplace[StringTrim[line], StartOfString ~~ DigitCharacter .. ~~ ("." | ")") ~~ " " -> ""]
orderedSplit[{}, collected_] := {Reverse[collected], {}}
orderedSplit[lines_List, collected_] := With[{line = First[lines]},
    Which[
        orderedItemQ[line],
            orderedSplit[Rest[lines], Prepend[collected, orderedText[line]]],
        collected =!= {} && listContinuationQ[line],
            orderedSplit[Rest[lines],
                Prepend[Rest[collected], First[collected] <> " " <> StringTrim[line]]],
        True,
            {Reverse[collected], lines}
    ]
]

(* a "$$ ... $$" line (or a "$$"-fenced block across multiple lines) is display math.
   Detected separately from inline "$math$" so it can become a centered DisplayFormula
   block rather than be mis-parsed as broken inline math on either side. *)
mathBlockOpenQ[line_String] := StringStartsQ[StringTrim[line], "$$"]
mathBlockClosedQ[line_String] := Block[{t = StringTrim[line]}, StringLength[t] >= 4 && StringStartsQ[t, "$$"] && StringEndsQ[t, "$$"]]

mathBlockGather[lines_List] := Block[{first = StringTrim @ First[lines], rest = Rest[lines], idx},
    If[ mathBlockClosedQ[First[lines]],
        {StringTrim @ StringTake[first, {3, -3}], rest},
        idx = FirstPosition[rest, l_String /; StringEndsQ[StringTrim[l], "$$"], {0}, {1}, Heads -> False];
        If[ idx === {0},
            (* unterminated: take everything after the opening "$$" as content *)
            {StringTrim @ StringDrop[first, 2], rest},
            With[{n = First[idx]},
                {StringTrim @ StringRiffle[Join[
                    {StringDrop[first, 2]},
                    rest[[1 ;; n - 1]],
                    {StringDrop[StringTrim[rest[[n]]], -2]}
                ], "\n"], rest[[n + 1 ;;]]}
            ]
        ]
    ]
]

(* blockquote lines start with ">". Consecutive lines are gathered and the marker
   ("> " or ">") stripped; the joined text becomes a "Quote" block. *)
blockquoteQ[line_String] := StringStartsQ[StringTrim[line], ">"]
quoteText[line_String] := StringReplace[StringTrim[line], StartOfString ~~ ">" ~~ (" " | "") -> ""]
quoteSplit[{}, collected_] := {Reverse[collected], {}}
quoteSplit[lines_List, collected_] := If[ blockquoteQ[First[lines]],
    quoteSplit[Rest[lines], Prepend[collected, quoteText[First[lines]]]],
    {Reverse[collected], lines}
]

(* a thematic break - a line of only "-", "_" or "*" (3+) between blank lines -
   is an explicit example separator (an ExampleDelimiter). Frontmatter "---" is
   already stripped, and "|---|" table rules contain "|", so neither matches.
   Tested by explicit character checks: in a string pattern a bare "*" is the
   wildcard metacharacter, so StringMatchQ[t, "*"..] would match anything. *)
separatorQ[line_String] := Block[{chars = Characters[StringTrim[line]]},
    Length[chars] >= 3 && MemberQ[{"-", "_", "*"}, First[chars, ""]] && Length[DeleteDuplicates[chars]] === 1
]

(* a continuation line under a list item: any non-empty, non-marker-starting
   line that does not itself open a new block. Standard markdown indents the
   continuation under the bullet's text column (2-4 spaces); we accept any
   leading whitespace and fall back to a plain non-list line, so wrapped
   prose under a bullet folds into the same item instead of breaking the list
   into "one item + a paragraph + another item + a paragraph + ..." (which is
   what the user sees as "6 bullets instead of 3"). *)
listContinuationQ[line_String] := StringLength[line] > 0 &&
    StringStartsQ[line, " " | "\t"] && StringTrim[line] =!= "" &&
    ! listItemQ[line] && ! orderedItemQ[line] && ! headingQ[line] &&
    ! fenceQ[line] && ! blockquoteQ[line] && ! mathBlockOpenQ[line]

(* collect a markdown list, folding indented continuation lines into the
   current item (joined with a single space, the way a CommonMark renderer
   would). `collected` is built in reverse - the first element is the current
   item being extended, so prepending a new item makes that the new "current". *)
listSplit[{}, collected_] := {Reverse[collected], {}}
listSplit[lines_List, collected_] := With[{line = First[lines]},
    Which[
        listItemQ[line],
            listSplit[Rest[lines], Prepend[collected, {listLineIndent[line], listText[line]}]],
        collected =!= {} && listContinuationQ[line],
            listSplit[Rest[lines],
                Prepend[Rest[collected],
                    MapAt[# <> " " <> StringTrim[line] &, First[collected], 2]]],
        True,
            {Reverse[collected], lines}
    ]
]

(* Turn the {indent, text} pairs listSplit collected into a List block, keeping
   Items as bare strings (every downstream reader still expects that) and adding
   a parallel Depths list so nesting-aware renderers can pick Item/Subitem/... . *)
listBlock[pairs_List] := <|
    "Type" -> "List",
    "Items" -> pairs[[All, 2]],
    "Depths" -> listDepths[pairs[[All, 1]]]
|>


(* GitHub-flavored tables: a "| a | b |" row whose next line is a "|---|---|"
   separator. Cells are split on "|" with the outer pipes trimmed. *)
tableRowLineQ[line_String] := StringContainsQ[line, "|"] && StringTrim[line] =!= "" && ! fenceQ[line] && ! headingQ[line]

tableSepQ[line_String] := StringContainsQ[line, "-"] && StringContainsQ[line, "|"] &&
    StringMatchQ[StringTrim[line], ("|" | ":" | "-" | " ") ..]

(* GitHub-flavored Markdown lets a cell contain a literal `|` by
   escaping it as `\|` - the backslash protects the pipe from being
   read as a cell delimiter. We split on UNescaped `|`s by temporarily
   swapping `\|` for a U+0001 sentinel character (never appears in
   normal Markdown), splitting on `|`, then swapping the sentinel back
   to a literal `|` in each cell. *)
splitTableRow[line_String] := Block[{sentinel = FromCharacterCode[1]},
    Map[
        StringReplace[#, sentinel -> "|"] &,
        StringTrim /@ StringSplit[
            StringReplace[StringTrim[StringTrim[line], "|"], "\\|" -> sentinel],
            "|"
        ]
    ]
]

tableSplit[{}, collected_] := {Reverse[collected], {}}
tableSplit[lines_List, collected_] := If[ tableRowLineQ[First[lines]],
    tableSplit[Rest[lines], Prepend[collected, First[lines]]],
    {Reverse[collected], lines}
]

(* markdown image on its own line: ![alt](path) or ![alt](path "effect"). The
   optional title is read as an effect keyword - "papertear" applies the front
   end's Paper Tear background to the inlined image's cell. *)
imageLineQ[line_String] := StringMatchQ[StringTrim[line], "![" ~~ ___ ~~ "](" ~~ ___ ~~ ")"]

parseImageTarget[rest_String] := Block[{
    m = StringCases[StringTrim[rest],
        StartOfString ~~ p : Shortest[Except["\""] ..] ~~ "\"" ~~ t : Shortest[___] ~~ "\"" ~~ EndOfString :> {StringTrim[p], t}, 1]
},
    If[m === {}, {StringTrim[rest], ""}, First[m]]
]

imageBlock[line_String] := First @ StringCases[StringTrim[line],
    "![" ~~ alt : Shortest[Except["]"] ...] ~~ "](" ~~ rest : Shortest[Except[")"] ..] ~~ ")" :>
        With[{pt = parseImageTarget[rest]}, <|"Type" -> "Image", "Alt" -> alt, "Path" -> First[pt], "Effect" -> Last[pt]|>]]

blockLoop[{}, acc_] := Reverse[acc]
blockLoop[lines_List, acc_] := Block[{line = First[lines], rest = Rest[lines], split},
    Which[
        StringTrim[line] === "",
            blockLoop[rest, acc]
        ,
        directiveLineQ[line],
            blockLoop[rest, Prepend[acc, <|"Type" -> "Directive", "Options" -> parseCellOptions[{line}]|>]]
        ,
        fenceQ[line],
            split = fenceSplit[rest, fenceLen[line]];
            blockLoop[Last[split], Prepend[acc, codeBlock[StringReplace[StringTrim[line], StartOfString ~~ ("`" ..) -> ""], First[split]]]]
        ,
        divOpenQ[line],
            split = divSplit[rest];
            blockLoop[Last[split], Prepend[acc,
                <|"Type" -> "Div",
                  "Kind" -> divKind[line],
                  "Blocks" -> parseBlocks[StringRiffle[First[split], "\n"]]|>
            ]]
        ,
        headingQ[line],
            blockLoop[rest, Prepend[acc, headingBlock[line]]]
        ,
        imageLineQ[line],
            blockLoop[rest, Prepend[acc, imageBlock[line]]]
        ,
        separatorQ[line],
            blockLoop[rest, Prepend[acc, <|"Type" -> "Separator"|>]]
        ,
        blockquoteQ[line],
            split = quoteSplit[lines, {}];
            blockLoop[Last[split], Prepend[acc, <|"Type" -> "Quote", "Text" -> StringRiffle[First[split], " "]|>]]
        ,
        mathBlockOpenQ[line],
            split = mathBlockGather[lines];
            blockLoop[Last[split], Prepend[acc, <|"Type" -> "MathBlock", "Text" -> First[split]|>]]
        ,
        tableRowLineQ[line] && rest =!= {} && tableSepQ[First[rest]],
            split = tableSplit[lines, {}];
            With[{rows = splitTableRow /@ First[split]},
                blockLoop[Last[split], Prepend[acc, <|"Type" -> "Table", "Header" -> First[rows], "Rows" -> Drop[rows, 2]|>]]
            ]
        ,
        listItemQ[line],
            split = listSplit[lines, {}];
            blockLoop[Last[split], Prepend[acc, listBlock[First[split]]]]
        ,
        orderedItemQ[line],
            split = orderedSplit[lines, {}];
            blockLoop[Last[split], Prepend[acc, <|"Type" -> "List", "Ordered" -> True, "Items" -> First[split]|>]]
        ,
        True,
            split = paraSplit[lines, {}];
            blockLoop[Last[split], Prepend[acc, <|"Type" -> "Prose", "Text" -> StringRiffle[First[split], " "]|>]]
    ]
]

(* Resolve "Directive" blocks (stand-alone "#| key: value" lines) into the block
   stream. A directive run that carries cell CONTENT ("file" or "boxes" - e.g. a
   saved Output cell) becomes its OWN code block; a content-free run (just style /
   tags) is a MODIFIER folded into the "Options" of the block that follows it,
   overriding same-named options. A trailing modifier-only run is dropped. *)
contentDirectiveQ[opts_] := KeyExistsQ[opts, "file"] || KeyExistsQ[opts, "boxes"]

attachDirectives[blocks_List] := Module[{out = {}, pend = <||>, flush},
    flush[] := (
        If[contentDirectiveQ[pend],
            AppendTo[out, <|"Type" -> "Code", "Lang" -> "wl", "Options" -> pend, "Code" -> ""|>]];
        pend = <||>
    );
    Do[
        If[ b["Type"] === "Directive",
            (* a key that repeats inside a content-bearing run starts a NEW
               standalone cell (consecutive Output runs are separated only by a
               blank line, which blockLoop drops) - flush the current one first *)
            If[ contentDirectiveQ[pend] && AnyTrue[Keys[b["Options"]], KeyExistsQ[pend, #] &],
                flush[]];
            pend = Join[pend, b["Options"]],
            If[ contentDirectiveQ[pend],
                flush[]; AppendTo[out, b],
                (* a modifier run (annotation / style / tags) attaches to the next
                   real content block; pass OVER a delimiter that carries no cell
                   metadata so a standalone "#| annotation:" placed just before a
                   "---" still lands on a cell instead of being dropped *)
                If[ pend =!= <||> && b["Type"] === "Separator",
                    AppendTo[out, b],
                    AppendTo[out, If[pend === <||>, b,
                        Append[b, "Options" -> Join[Lookup[b, "Options", <||>], pend]]]];
                    pend = <||>
                ]
            ]
        ],
        {b, blocks}
    ];
    flush[];
    out
]

(* blockLoop and its sibling splitters (fenceSplit, paraSplit, listSplit, ...)
   recurse once per source line, and Wolfram does not tail-call optimize -
   the default $RecursionLimit of 1024 trips on any document longer than
   roughly a thousand lines. Lift the limit to scale with the document
   (8x the line count, capped, with a 10000 floor so short docs are
   unaffected) so a real-world tutorial of tens of thousands of lines
   parses without aborting. Rewriting the parser as an iterative
   While-loop would be cleaner long-term; this is the minimal patch
   that keeps the parser useful on big inputs. *)
parseBlocks[body_String] := Block[
    {lines = StringSplit[body, "\n"], $RecursionLimit},
    $RecursionLimit = Max[10000, 8 * Length[lines], Replace[$RecursionLimit, Except[_Integer] -> 0]];
    attachDirectives[blockLoop[lines, {}]]
]

(* drop HTML/markdown comments (e.g. "<!-- => 21. -->" output annotations).
   Only strips from prose segments - content inside fenced code blocks (```)
   is left untouched, so a string literal in WL source that happens to
   contain "<!-- ... -->" survives a walker-twin -> rebuild round trip
   instead of being corrupted by the global regex. *)
stripComments[s_String] := Module[{lines = StringSplit[s, "\n", All], out = {}, inFence = False, openLen = 0, buf = {}},
    flushProse[] := If[buf =!= {},
        AppendTo[out, StringReplace[StringRiffle[buf, "\n"],
            "<!--" ~~ inner : Shortest[___] ~~ "-->" :>
                (* a multi-line "<!-- #| annotation: ... -->" is hard-wrapped prose;
                   join the wrapped lines into one so the line-based block parser
                   keeps the whole directive value, not just its first line *)
                If[StringStartsQ[StringTrim[inner], "#|"],
                    StringReplace[StringTrim[inner], "\n" ~~ WhitespaceCharacter ... -> " "],
                    ""]]];
        buf = {}
    ];
    Do[
        Which[
            ! inFence && fenceQ[line], (* open *)
                flushProse[]; inFence = True; openLen = fenceLen[line]; AppendTo[out, line],
            inFence && fenceQ[line] && fenceLen[line] >= openLen, (* close *)
                AppendTo[out, line]; inFence = False; openLen = 0,
            inFence, (* inside fence - preserve verbatim *)
                AppendTo[out, line],
            True, (* prose line *)
                AppendTo[buf, line]
        ],
        {line, lines}
    ];
    flushProse[];
    StringRiffle[out, "\n"]
]

litParse[text_String] := Block[{fm = extractFrontmatter[text]},
    <|"Metadata" -> First[fm], "Blocks" -> parseBlocks[stripComments[Last[fm]]]|>
]

(* === source resolution ===
   The entry accepts a local file path, an http(s) URL, or a raw markdown
   string. Resolution yields the text, a base for "#| file:" includes, a name
   for the default output, and whether the source is a local file. *)

urlQ[s_String] := StringMatchQ[s, ("http://" | "https://") ~~ ___]

joinSource[base_String, path_String] := If[ urlQ[base],
    StringTrim[base, "/"] <> "/" <> path,
    FileNameJoin[{base, path}]
]

resolveSource[input_String] := Which[
    urlQ[input],
        <|"Text" -> Import[input, "Text"], "Base" -> StringReplace[input, RegularExpression["/[^/]*$"] -> ""], "Name" -> FileBaseName @ Last @ StringSplit[input, "/"], "Local" -> False, "Id" -> input|>
    ,
    FileExistsQ[input],
        <|"Text" -> Import[input, "Text"], "Base" -> DirectoryName[input], "Name" -> FileBaseName[input], "Local" -> True, "Id" -> input|>
    ,
    True,
        <|"Text" -> input, "Base" -> Directory[], "Name" -> "Notebook", "Local" -> False, "Id" -> input|>
]

(* a code cell carrying a "file" option inlines that file's contents as its
   body, resolved (file or URL) relative to the document; a markdown image block
   imports its image (file or URL) relative to the document. Both resolutions
   happen here because the document base is known. *)
resolveBlock[b_Association, base_String] := Which[
    (* a ".wxf" include is raw box data (a saved Output cell's BoxData), not text:
       import the boxes and mark the cell boxes-literal so it renders unevaluated
       through the box path (the "#| style: Output" directive then makes it an
       Output cell). This is the large-output counterpart of inline "#| boxes". *)
    b["Type"] === "Code" && KeyExistsQ[b["Options"], "file"] &&
        StringEndsQ[ToLowerCase[b["Options"]["file"]], ".wxf"],
        Join[b, <|"Boxes" -> Quiet @ Import[joinSource[base, b["Options"]["file"]], "WXF"],
                  "Options" -> Append[b["Options"], "boxes" -> True]|>],
    b["Type"] === "Code" && KeyExistsQ[b["Options"], "file"],
        Append[b, "Code" -> Import[joinSource[base, b["Options"]["file"]], "Text"]],
    b["Type"] === "Image",
        Append[b, "Image" -> Quiet @ Import[joinSource[base, b["Path"]]]],
    True, b
]

resolveIncludes[blocks_List, base_String] := Map[resolveBlock[#, base] &, blocks]

(* === sections === *)

(* Canonicalise a heading title to its section-key form. The doc-template's
   ExampleSection cells ship with "&" in titles ("Properties & Relations",
   "Scope & Additional Elements"); some hand-authored .md files use the
   word "and" instead. Normalise both to the same canonical key so a doc
   that round-trips through NotebookToMarkdown (which recovers the
   template's literal "&" title) is re-recognised on the next forward
   build. *)
sectionKey[text_String] := StringReplace[ToLowerCase[text], " & " -> " and "]

sectionsFrom[blocks_List] := Block[{step, init},
    init = <|"key" -> "", "acc" -> <||>, "pend" -> <||>|>;
    step[state_, b_] := Which[
        b["Type"] === "Heading" && b["Level"] <= 2,
            (* A "#| " directive on a section heading ("#| annotation:" before
               "## Details", say) has no header cell of its own on a structured page -
               the heading maps to a template slot, not a visible cell. Carry the
               heading's style / tags / annotation to the section's FIRST content
               block, where the block builders' applyBlockMeta lands it on the first
               cell the section produces (e.g. the first Notes cell). Directives that
               only make sense on a code cell (eval / file / ...) are not carried. *)
            With[{k = sectionKey[b["Text"]]},
                <|"key" -> k, "acc" -> Append[state["acc"], k -> {}],
                  "pend" -> KeyTake[Lookup[b, "Options", <||>], {"style", "tags", "annotation"}]|>]
        ,
        state["key"] === "",
            state
        ,
        True,
            (* stash the heading's directives on the first block under a private
               "headingMeta" key; applyBlockMeta lands them on that block's FIRST
               cell only, so a "## Details" annotation is one note, not one per item *)
            <|"key" -> state["key"],
              "acc" -> MapAt[Append[#, If[state["pend"] === <||>, b,
                     Append[b, "Options" -> Append[Lookup[b, "Options", <||>], "headingMeta" -> state["pend"]]]]] &,
                 state["acc"], Key[state["key"]]],
              "pend" -> <||>|>
    ];
    Fold[step, init, blocks]["acc"]
]

(* "#| boxes: true" reads the cell content as a literal box expression
   (parsed by ToExpression, not evaluated) and splices it directly into
   BoxData - the author writes raw RowBox / GridBox / TemplateBox /
   TagBox / TooltipBox and the converter renders those boxes unchanged.
   A boxes cell is non-executable by definition, so executableQ excludes
   it the same way "#| eval: false" is excluded - the non-executable
   rendering path then dispatches in nonExecutableCell to emit a boxed
   Input cell instead of a Program-styled plain-text cell. *)
(* "#| boxes: true" takes the fence body as the box expression; "#| boxes: <expr>"
   carries the expression in the option value itself (used by the comment carrier,
   which has no fence body - e.g. a small Output cell inlined in a metadata comment). *)
boxesLiteralQ[b_] := With[{v = Lookup[b["Options"], "boxes", False]}, TrueQ[v] || StringQ[v]]

executableQ[b_] := b["Type"] === "Code" && MemberQ[{"wl", "wolfram", "mathematica"}, b["Lang"]] && TrueQ[Lookup[b["Options"], "eval", True]] && ! boxesLiteralQ[b]

(* parse the cell text as a Wolfram expression with no evaluation and
   return it as-is for use as box data; on a parse failure fall back to
   the raw string so the author sees the source rather than nothing. *)
cellLiteralBoxes[code_String] := With[{e = Quiet @ ToExpression[code, InputForm, HoldComplete]},
    Replace[e, {HoldComplete[expr_] :> expr, _ :> code}]
]

(* non-executable code-block rendering: an Input cell whose BoxData is the
   literal parsed box expression for `#| boxes: true`; a non-evaluated
   Wolfram-language fence keeps the Input style (issue #17 - the spec in
   docs/formatting.md reads "keep the input cell" for #| eval: false);
   genuinely foreign-language fences (bash, python, ...) render as a
   plain-text Program cell. *)
(* box data for a boxes-literal cell: imported ".wxf" boxes when present (large
   output), else the "#| boxes: <expr>" option value, else the fence body. *)
cellBoxesOf[b_] := With[{v = Lookup[b["Options"], "boxes", False]},
    Which[
        KeyExistsQ[b, "Boxes"], b["Boxes"],
        StringQ[v], cellLiteralBoxes[v],
        True, cellLiteralBoxes[b["Code"]]
    ]]

nonExecutableCell[b_] := applyCellMeta[
    Which[
        boxesLiteralQ[b],
            Cell[BoxData[cellBoxesOf[b]], "Input"],
        MemberQ[{"wl", "wolfram", "mathematica"}, b["Lang"]],
            Cell[BoxData[inputBoxes[b["Code"]]], "Input"],
        True,
            Cell[b["Code"], "Program"]
    ],
    Lookup[b, "Options", <||>]
]

sectionCells[sections_, key_] := Cases[Lookup[sections, key, {}], b_ /; executableQ[b]]

sectionCode[sections_, key_] := StringRiffle[#["Code"] & /@ sectionCells[sections, key], "\n\n"]

(* Concatenate the prose paragraphs of a section, preserving any inline
   markdown (backticks / bold / italic / links / math) - downstream renderers
   route the result through inlineTextData so they handle the markup; the
   legacy backtick-stripping done here used to defend a plain-string cell
   path that no longer exists. *)
sectionText[sections_, key_] := StringRiffle[
    Cases[Lookup[sections, key, {}], b_ /; b["Type"] === "Prose" :> b["Text"]],
    " "
]

(* === notebook evaluation with a cumulative-hash cache ===
   All executable cells are evaluated in document order, threading state, so a
   cell's cache key depends on every cell before it. The "EvaluateSeparator"
   MarkdownToNotebook option picks the granularity of isolation between
   cells:
     Automatic - reset at "---" thematic breaks and at every heading,
                 at any level (the default - each (sub)section runs
                 in a clean context). A reset clears only symbols
                 INTRODUCED AFTER the document's "## Definition" section
                 has run; the definition's symbols (the FunctionResource
                 function, helper bindings) persist across every later
                 section. The protected baseline is snapshotted at the
                 first reset that follows the definition section, so an
                 example that introduces a temp local helper is wiped
                 between sections but the resource's function is not.
     All       - reset before every executable cell, so each cell runs
                 in a fresh context with its hash depending only on
                 its own code (maximum isolation, minimum cache reuse).
                 The same definition-preservation rule applies.
     None      - no reset; the whole notebook shares one eval context
                 and the cumulative-hash chain spans every cell.
                 Supported but not recommended: per-example helpers
                 leak across every later section, so a stray binding in
                 ## Basic Examples may collide with names in ## Scope.
                 Put binding that legitimately needs to cross sections
                 in the document's ## Definition section, and let
                 Automatic preserve only it.
   The input list interleaves executable cells, "Separator" blocks, and
   "Heading" blocks; the returned hash list has one entry per executable
   cell (boundaries contribute a reset, not a hash). *)

resetBoundaryQ[mode_, item_] := Switch[mode,
    None,        False,
    All,         MatchQ[item["Type"], "Separator" | "Heading"] || executableQ[item],
    _,           MatchQ[item["Type"], "Separator" | "Heading"]
]

cumulativeHashes[mode_, items_List] := Block[{acc = "", hashes = {}},
    Scan[
        item |-> (
            If[resetBoundaryQ[mode, item], acc = ""];
            If[executableQ[item],
                acc = acc <> mdSep <> item["Code"]; AppendTo[hashes, Hash[acc]]
            ]
        ),
        items
    ];
    hashes
]

(* the light/dark mode example renderings are pinned to. Default light (the
   deployed notebook is light); the markdown-out twin sets it to "Dark". Guard the
   initialization with ValueQ so re-loading this file (the Definition cell inlines
   and evaluates the whole .wl during conversion) does not clobber an override. *)
If[! ValueQ[$lightDark], $lightDark = "Light"]

(* conversion nesting depth. A self-referential example (a doc whose example calls
   MarkdownToNotebook on a document, e.g. the function on its own GitHub source)
   would otherwise re-evaluate that document's examples, and so on without end. So
   only the top-level conversion evaluates examples; a nested one builds the
   notebook with its example cells left unevaluated (input only). *)
If[! ValueQ[$convertDepth], $convertDepth = 0]

(* the notebook a result stands for (a Notebook expression, or the open notebook of
   a NotebookObject), pinned to the current mode. The Resource templates
   (FunctionResource / Example / Data) come from DefinitionNotebookClient with
   LightDark -> "Light" already baked in; appending a second LightDark would
   leave both in the option sequence and the front end would honour the first
   (Light) one, so strip any existing LightDark before setting ours. *)
resultNotebook[res_] := Block[{nb = If[MatchQ[res, _NotebookObject], NotebookGet[res], res]},
    nb /. Notebook[c_, o___] :> Notebook[c, Sequence @@ DeleteCases[{o}, LightDark -> _], LightDark -> $lightDark]
]

(* output for an evaluated cell. A whole notebook has no faithful inline form -
   inlining its cells breaks the surrounding layout (a Title/Section renders
   document-wide; a CellFrame is just a per-cell option, it does not bound a group).
   So a produced notebook is shown as a *rendered thumbnail*: a NotebookObject (the
   notebook itself, opened with NotebookPut, as published WFR functions return) is
   rasterized and closed, the WFR-canonical display; a bare Notebook *expression*
   opts into the same rasterization with "#| screenshot: true" (otherwise it is
   shown as its literal expression boxes). *)
(* keep a rasterized cell image under the resource Check's "large cell area"
   threshold (~500k pixels). Cap both the long dimension and the area to keep
   the cell from tripping LargeCellBounds while still showing the content
   readably. *)
$rasterMaxLongDim = 1200
$rasterMaxArea = 480000
capRaster[img_] := If[ ! ImageQ[img], img,
    Block[{w, h, longDim, area, scale},
        {w, h} = ImageDimensions[img];
        longDim = Max[w, h];
        area = w h;
        scale = Min[1, $rasterMaxLongDim / longDim, Sqrt[$rasterMaxArea / area]];
        If[scale < 1, ImageResize[img, Round[scale {w, h}]], img]
    ]
]

outputBoxes[res_, opts_] := Which[
    res === Null, Null,
    MatchQ[res, _NotebookObject],
        (* a whole-notebook thumbnail can be enormous; rasterize at a lower
           resolution and cap the height so the cell does not trip the analysis
           "huge raster" / "large screen area" checks, while still showing the
           entire notebook. *)
        With[{img = Quiet @ Rasterize[resultNotebook[res], ImageResolution -> 96]},
            Quiet @ NotebookClose[res];
            ToBoxes @ capRaster[img]],
    TrueQ[Lookup[opts, "screenshot", False]] && MatchQ[res, _Notebook],
        ToBoxes @ capRaster @ Quiet @ Rasterize[resultNotebook[res], ImageResolution -> 144],
    True, ToBoxes[res]
]

(* === message capture (box level) ===
   captureCellRun installs an Internal`HandlerBlock["Message"] handler rather than
   redirecting $Messages to a text file, so a message is captured as the same box
   structure a notebook would show. handleMsg reformats each shown message from its
   template + args: the name is a "MessageName"-styled token and each "`n`" slot is
   the nth arg boxified - a string inserts verbatim, a RawBoxes inlines its boxes
   (so ResourceFunctionMessage's styled name renders as real boxes instead of
   dumping literal "RawBoxes[StyleBox[...]]"), anything else goes through ToBoxes.
   The General::tag template is the fallback, matching the kernel. *)
msgArgBox[s_String] := s
msgArgBox[RawBoxes[b_]] := b
msgArgBox[e_] := ToBoxes[e]
SetAttributes[messageNameString, HoldFirst]
messageNameString[s_Symbol] := SymbolName[Unevaluated[s]]
messageNameString[o_] := ToString[Unevaluated[o], InputForm]
slotFill[tmpl_String, args_List] := Replace[
    StringSplit[tmpl, "`" ~~ ds : (DigitCharacter ..) ~~ "`" :> msgSlot[FromDigits[ds]]],
    msgSlot[i_] :> If[1 <= i <= Length[args], msgArgBox[args[[i]]], ""], {1}]
messageBoxData[name_String, tmpl_, args_List] := RowBox[Flatten[{
    StyleBox[name, "MessageName"], ": ",
    If[StringQ[tmpl], slotFill[tmpl, args], Riffle[msgArgBox /@ args, " "]]}, 1]]
(* Quiet the body: building the box (ToBoxes of an arg, the template lookup) must
   not itself fire a message, or the still-active handler would re-enter and loop.
   A message fired here is Quiet'd -> reported to the handler as shown=False ->
   falls to the no-op below, so there is no recursion. *)
handleMsg[Hold[Message[MessageName[sym_, tag_String], margs___], True]] := Quiet @
    AppendTo[msgs, messageBoxData[
        messageNameString[Unevaluated[sym]] <> "::" <> tag,
        With[{t = MessageName[sym, tag]}, If[StringQ[t], t, MessageName[General, tag]]],
        {margs}]]
handleMsg[_] := Null

(* legacy: an OLD cache entry stored messages as plain text, where a styled
   RawBoxes name dumped as literal "RawBoxes[StyleBox[RowBox[{name, ::, tag}],
   MessageName]]" - recover "name::tag" so a cached page still reads cleanly. *)
cleanMessageText[s_String] := StringReplace[s,
    "RawBoxes[StyleBox[RowBox[{" ~~ name : Shortest[__] ~~ ", ::, " ~~
        tag : Shortest[__] ~~ "}], MessageName]]" :> StringTrim[name] <> "::" <> StringTrim[tag]]

(* a captured message -> a notebook "Message" cell: box data (the new box-level
   capture) wraps directly; a legacy text string is cleaned and wrapped. *)
messageCell[s_String] := Cell[cleanMessageText[s], "Message", "MSG"]
messageCell[box_] := Cell[BoxData[box], "Message", "MSG"]

(* Captured Print / Echo output -> a notebook "Print" cell.
   Print is intercepted by Block-shadowing the symbol (rebinding $Output
   does NOT re-route Print under `wl -f`: it writes straight to stdout via
   a hardcoded channel; only a local Block-binding on the Protected symbol
   intercepts). Each arg is coerced individually: a string splices as a
   literal box leaf (matching notebook Print's "unquoted strings"
   semantics), any other expression goes through ToBoxes - so
   Print[graphic] / Print[image] / Print[dataset] / Print[typeset] all
   render correctly in the resulting cell instead of collapsing to
   "-Graphics-" the way a `ToString` round-trip would. *)
printArgBoxes[s_String] := s
printArgBoxes[expr_] := ToBoxes[expr]

printCellFromArgs[args_List] := With[{bs = printArgBoxes /@ args},
    Cell[BoxData[If[Length[bs] === 1, First[bs], RowBox[bs]]], "Print"]
]

(* Backwards-compat: old cache entries stored Print output as plain text
   chunks. Wrap any string entries in a Print cell on the way out. *)
asPrintCell[s_String] := Cell[s, "Print"]
asPrintCell[c_Cell] := c
asPrintCell[other_] := Cell[ToString[other, InputForm], "Print"]

(* box -> plain text, for the markdown twin's blockquote of a captured message
   (a StyleBox keeps only its content; a RowBox concatenates its parts). *)
msgBoxText[s_String] := s
msgBoxText[RowBox[xs_List]] := StringJoin[msgBoxText /@ xs]
msgBoxText[(StyleBox | TagBox | InterpretationBox | FrameBox)[b_, ___]] := msgBoxText[b]
msgBoxText[b_] := ToString[b, InputForm]

(* Plain-text rendering of captured messages / prints for the markdown twin.
   A box-level message renders via msgBoxText; a legacy text string is cleaned.
   Print cells may be rich - a string-only Print becomes a blockquote, anything
   richer rasterises to a screenshot image. *)
messageMd[s_String] := "> " <> StringReplace[StringTrim[cleanMessageText[s]], "\n" -> "\n> "]
messageMd[box_] := With[{t = StringTrim[msgBoxText[box]]},
    If[t === "", "", "> " <> StringReplace[t, "\n" -> "\n> "]]]

(* Extract a textual form from a captured Print cell, or Missing if it
   carries rich content (a GraphicsBox, a Dataset, a TemplateBox, ...).
   Used by the twin renderer to decide between a blockquote and a
   rasterised image. *)
printTextForm[s_String] := s
printTextForm[Cell[s_String, "Print", ___]] := s
printTextForm[Cell[BoxData[s_String], "Print", ___]] := s
printTextForm[Cell[BoxData[RowBox[lst_List]], "Print", ___]] /;
    AllTrue[lst, StringQ] := StringJoin[lst]
printTextForm[_] := Missing["Rich"]

(* Capture EVERYTHING a cell's evaluation would produce in a real notebook,
   without relying on the FE-driven NotebookEvaluate (which hangs in headless
   `wl` since there is no FE->kernel link to drive it). Three complementary
   mechanisms cover the four observable channels:

   - Messages: redirect $Messages to a private write stream. Captures every
     fired message including the OptionValue::optnf / General::newsym noise
     Wolfram's framework fires per Plot (mostly suppressed by $Off / Stop /
     Internal`InheritedBlock in Charting). Redirecting the print stream is
     the *one* mechanism that respects all of those - whatever the kernel
     decides to actually print, we capture verbatim.

   - Print / Echo: Block-shadow the symbols. In script mode ($Output is
     {OutputStream[stdout]}, no FE link), rebinding $Output does NOT
     re-route Print - it writes straight to stdout via a hardcoded channel.
     A local Block-binding on the Protected symbol works inside the
     dynamic scope without touching the global definition.

   - Intermediate Output values: parse the cell source into top-level
     statements (Hold[s1, s2, ..., sN]) and evaluate each in order. A
     statement whose held form is CompoundExpression[..., Null] (a
     `;`-terminated source line) suppresses its Output cell - matching
     notebook semantics. Plain expressions emit one Output per statement,
     so a cell with `1+1\n2+2\n3+3` round-trips with three Output cells,
     not just the last value Get returned previously.

   - CellPrint: Block-shadow to capture cells injected by EchoFunction,
     ResourceObject scrapers, or hand-written CellPrint calls. The captured
     cells render in-line right after the Print/Echo cells.

   Returns <|"outs" -> {boxes-or-Missing per non-suppressed statement},
              "msgs" -> {message text, ...},
              "prints" -> {print text, ...},
              "cells" -> {injected cell, ...}|>.
   Failed Get / parse returns "outs" -> {Missing[]} so callers downstream
   still see the failure as a no-output cell rather than a crash. *)
captureCellRun[code_String, opts_Association : <||>] := Block[{stmts, outs, cellsExtra, msgs, prints},
    stmts = Quiet @ ToExpression[code, InputForm, Hold];
    If[Head[stmts] =!= Hold, stmts = Hold[code]];  (* parse failure: re-run for the message *)
    outs = {};
    cellsExtra = {};
    prints = {};
    msgs = {};
    (* $Messages -> {} suppresses the kernel's default text output; messages are
       captured at the box level by the Internal`HandlerBlock below (handleMsg
       AppendTo's the Block-local msgs via dynamic scope). *)
    Block[{$Messages = {}, Print, Echo, CellPrint},
        (* Print accumulates a real Cell built from the args, not a text
           chunk - so Print[graphics], Print[image], Print[dataset], or
           Print["count: ", n] each render correctly downstream. *)
        Print[args___] := (AppendTo[prints, printCellFromArgs[{args}]]; Null);
        Echo[e_] := (Print[">> ", e]; e);
        Echo[e_, label_] := (Print[">> ", label, " ", e]; e);
        Echo[e_, label_, f_] := (Print[">> ", label, " ", f[e]]; e);
        CellPrint[c_Cell] := (AppendTo[cellsExtra, c]; Null);
        CellPrint[cs_List] := (cellsExtra = Join[cellsExtra, Cases[cs, _Cell]]; Null);
        (* Walk statements: each held position is extracted with Extract,
           which preserves the Hold wrapper so we can inspect its surface
           form before releasing it. A CompoundExpression[..., Null] tail
           is the source's "no output" mark - skip emission for that. The
           HandlerBlock captures every message fired inside this walk. *)
        Internal`HandlerBlock[{"Message", handleMsg},
            Do[
                With[{heldStmt = Extract[stmts, i, Hold]},
                    If[ MatchQ[heldStmt, Hold[CompoundExpression[___, Null]]],
                        (* suppressed - evaluate for side effects, no Output *)
                        ReleaseHold[heldStmt],
                        (* Quiet Syntax:: while rendering the result: typesetting a
                           TraditionalForm[HoldForm[...]] display label (e.g. a Manipulate Item
                           showing a vector/fraction) reparses its ASCII form and fires a spurious
                           Syntax::sntx, spamming the build though the notebook is correct (issue
                           #59). The statement itself already parsed at the top-level ToExpression,
                           so a syntax message here is never a real parse error. *)
                        AppendTo[outs, Quiet[outputBoxes[ReleaseHold[heldStmt], opts],
                            {Syntax::sntx, Syntax::sntxi, Syntax::sntxb, Syntax::tsntxi}]]
                    ]
                ],
                {i, Length[stmts]}
            ]
        ]
    ];
    <|"outs" -> outs, "msgs" -> msgs, "prints" -> prints, "cells" -> cellsExtra|>
]

(* Snapshot every symbol currently bound in the document context tree -
   "ctx`*" matches symbols in ctx; "ctx`**`*" matches symbols in every
   sub-context underneath ctx (a single "ctx`**" only matches the
   immediate context). *)
docContextSymbols[ctx_String] := Join[
    Quiet @ Names[ctx <> "*"],
    Quiet @ Names[ctx <> "**`*"]
]

(* A reset clears every symbol introduced AFTER the protected baseline was
   captured, drops the cumulative code chain so the next cell's cache key
   starts fresh, and ClearSystemCache[]s so any AutoMemoization / Once
   entries do not leak. The baseline (state["protected"]) is the set of
   symbols defined by the document's "## Definition" section - captured
   at the first reset boundary that follows that section (see accumEval).
   While protected is still None, the doc hasn't crossed the boundary
   yet, so nothing is cleared - this lets all "## Definition" code finish
   without losing its own bindings on the intervening heading boundary
   inside the definition area.  The host session's Global` and unrelated
   paclets are left alone - only the per-doc context tree is wiped. *)
resetState[state_] := If[
    state["protected"] === None,
    (* pre-definition area: cumulative code chain still resets so cache
       keys don't span the boundary, but we keep every bound symbol. *)
    (ClearSystemCache[]; <|state, "code" -> ""|>),
    Block[{toRemove = Complement[docContextSymbols[state["ctx"]], state["protected"]]},
        If[toRemove =!= {}, Quiet @ ClearAll @@ toRemove];
        ClearSystemCache[];
        <|state, "code" -> ""|>
    ]
]

evalCell[state_, b_] := Block[{code = state["code"] <> mdSep <> b["Code"], captured},
    (* captureCellRun parses b["Code"] into top-level statements via
       ToExpression[..., Hold] so every statement runs in document order
       and each non-`;`-suppressed value contributes its own Output - matching
       how a notebook cell with multiple expressions renders multiple Out[n]s.
       outputBoxes is applied per-value inside the capture (the cell's options
       e.g. "screenshot" / "tear" / "image" route through to each output). *)
    captured = captureCellRun[b["Code"], b["Options"]];
    <|state, "code" -> code,
      "out" -> Append[state["out"], Hash[code] -> captured]|>
]

(* A reset boundary item that follows the definition section is the moment
   we lock in the protected baseline: snapshot every symbol currently bound
   in the doc context tree and record it as state["protected"]. The
   detection is simple - this fires the first time we see a Heading whose
   text matches a known example section ("Basic Examples", "Scope", etc.)
   after at least one executable cell has run. For docs without a
   definition section the baseline ends up empty (snapshot of an empty
   context), which is the correct degenerate case: every reset clears
   everything, the historical Automatic behaviour. *)
$exampleHeadingMatchQ[text_String] := MemberQ[$exampleOrder, ToLowerCase[StringTrim[text]]]
$exampleHeadingMatchQ[_] := False

captureProtectedQ[state_, b_] :=
    state["protected"] === None && state["primed"] === True &&
        b["Type"] === "Heading" && $exampleHeadingMatchQ[b["Text"]]

(* fold step: per "EvaluateSeparator" mode, reset before this item if it is
   a boundary, then evaluate if it is an executable cell. Separator /
   Heading blocks just trigger a reset; in mode All every executable cell
   triggers a reset before its own evaluation. Capture the protected
   baseline before clearing if this boundary marks the transition into
   the first example section. *)
accumEval[state0_, b_] := Block[{state = state0, s},
    If[ captureProtectedQ[state, b],
        state = <|state, "protected" -> docContextSymbols[state["ctx"]]|>
    ];
    s = If[resetBoundaryQ[state["mode"], b], resetState[state], state];
    If[executableQ[b],
        With[{s2 = evalCell[s, b]}, <|s2, "primed" -> True|>],
        s
    ]
]

(* Pre-load every package whose first use during evaluation would otherwise
   fire setup-time chatter (General::newsym for each interned symbol, ::shdw
   for cross-context shadowing, Pattern::patv from package-private code) -
   that chatter then fires HERE, outside the per-cell capture scope, where
   Quiet swallows it. Without preloading, the first cell that touches such a
   package "owns" hundreds of bookkeeping messages that have nothing to do
   with what the cell's author wrote, and the FE doesn't show them either
   (by the time the user clicks Run the package is already loaded).

   The list spans:
     - $framePackages: the resource framework Wolfram lazy-loads on first
       use of ResourceObject[EvaluationNotebook[]] /
       DefinitionNotebookClient`Check... / DocumentationBuild. The pair
       ResourceSystemClient`DefinitionNotebook` and DefinitionNotebookClient`
       defines dozens of overlapping symbol names and triggers a flood of
       ::shdw warnings unless both are loaded together up front.
     - the document's own context path (so a resource that depends on a
       paclet has the paclet ready when an example calls it).

   A genuine load failure for any of these is benign here - we just don't
   pre-load it, and the first cell that actually uses it surfaces the real
   error in context. *)
$framePackages = {
    "ResourceSystemClient`",
    "DefinitionNotebookClient`",
    "DocumentationTools`"
}
preloadContextPath[ctxPath_List] := (
    Quiet @ Scan[
        Quiet @ Check[Needs[#], Null] &,
        DeleteDuplicates @ Select[Join[$framePackages, ctxPath], # =!= "System`" &]
    ];
    (* A paclet may keep its public symbols in subcontexts of its primary
       context (see symbolInContextQ); the loader normally prepends those to
       $ContextPath as it Gets each subpackage, but when the paclet is already
       loaded the Needs above is a no-op and the example evaluator's
       Block-scoped $ContextPath never sees them - so bare documented names
       would parse into the private example context and stay unevaluated.
       Put every non-Private subcontext of the requested contexts on the path
       explicitly. A context is a private-implementation context when its final
       segment ends in "Private" - test the whole string with StringEndsQ so
       this catches BOTH the conventional `Foo`Private`` and the named
       `Foo`BarPrivate`` forms (a paclet that keeps LaTeX internals in
       `Foo`LaTeXPrivate`` must not have that context leak onto the example
       path, or its scoped temporaries - a$, b$ from a Function[{a,b},...] -
       become visible and fire spurious General::shdw when a cell evaluates). *)
    $ContextPath = DeleteDuplicates @ Join[
        $ContextPath,
        Flatten @ Map[
            Function[ctx, Select[Contexts[ctx <> "*"], ! StringEndsQ[#, "Private`"] &]],
            DeleteCases[ctxPath, "System`"]
        ]
    ]
)

(* Install a one-symbol forwarding alias in the per-doc context so example
   cells in a self-referential document can call MarkdownToNotebook
   unqualified WITHOUT having Context[MarkdownToNotebook] on $ContextPath
   (which would expose every internal helper and Block local as a public
   symbol the example can collide with - see issue #5).

   Sets the OwnValue of <ctx>`MarkdownToNotebook to the real
   MarkdownToNotebook symbol, so an example's `MarkdownToNotebook[...]`
   resolves to <ctx>`MarkdownToNotebook (via $Context lookup at parse
   time), then evaluates to MarkdownToNotebook[...] via the OwnValue.

   $Context is rebound to ctx and $ContextPath stripped to System` for
   the ToExpression call so the LHS interns into ctx (creating
   ctx`MarkdownToNotebook) while the RHS - a fully qualified name -
   resolves to the real symbol regardless. *)
installSelfAlias[ctx_String] := With[{realName = Context[MarkdownToNotebook] <> "MarkdownToNotebook"},
    Block[{$Context = ctx, $ContextPath = {"System`"}},
        Quiet @ ToExpression["MarkdownToNotebook = " <> realName, InputForm]
    ]
]

(* a front end is active for the whole pass so an example may open the notebook it
   produces (NotebookPut) and have its thumbnail captured (see outputBoxes). *)
evaluateAll[items_List, ctx_String, ctxPath_List, mode_] := Block[{$Context = ctx, $ContextPath = ctxPath},
    preloadContextPath[ctxPath];
    UsingFrontEnd[Fold[accumEval,
        <|"code" -> "", "out" -> <||>, "ctx" -> ctx, "mode" -> mode,
          "protected" -> None, "primed" -> False|>,
        items]]["out"]
]

(* attach each executable block's output (by cumulative hash) so builders read
   block["OutputBoxes"] / block["Messages"] directly instead of recomputing hashes.
   The cache entry is normally an Association <|"out" -> boxes, "msgs" -> {...}|>;
   accept the legacy raw-boxes form too (older cache entries with no message data). *)
annotateOutputs[blocks_List, hashes_List, outputs_] := Block[{i = 0, walk},
    walk[b_] := Which[
        executableQ[b],
            Block[{entry, outsList, msgs, prints, cellsExtra},
                i += 1;
                entry = Lookup[outputs, hashes[[i]], Missing[]];
                (* Three cache shapes to accommodate:
                     - new: <|"outs" -> {boxes...}, "msgs" -> ..., "prints" -> ..., "cells" -> {...}|>
                     - intermediate: <|"out" -> boxes, "msgs" -> ..., "prints" -> ...|>
                     - legacy: bare boxes (no association)
                   The "outs" list may be empty (a cell whose only statements
                   are `;`-suppressed) - that's intentional, render as
                   input + prints + messages with no Output cell. *)
                {outsList, msgs, prints, cellsExtra} = Which[
                    AssociationQ[entry] && KeyExistsQ[entry, "outs"],
                        {entry["outs"], Lookup[entry, "msgs", {}],
                         Lookup[entry, "prints", {}], Lookup[entry, "cells", {}]},
                    AssociationQ[entry] && KeyExistsQ[entry, "out"],
                        {{entry["out"]}, Lookup[entry, "msgs", {}],
                         Lookup[entry, "prints", {}], {}},
                    True,
                        {{entry}, {}, {}, {}}
                ];
                Append[Append[Append[Append[
                    Append[b, "OutputBoxes" -> First[outsList, Missing[]]],
                    "Outputs" -> outsList],
                    "Messages" -> msgs],
                    "Prints" -> prints],
                    "ExtraCells" -> cellsExtra]
            ],
        b["Type"] === "Div",
            (* recurse: walk the Div's inner blocks, the counter `i`
               continues from the outer walk so each cell's hash and
               output map line up. *)
            Append[b, "Blocks" -> walk /@ b["Blocks"]],
        True, b
    ];
    walk /@ blocks
]

(* === notebook cell builders === *)

(* known example-section keys, in canonical render order. The list is the union of
   conventions across templates (FunctionResource uses Basic / Scope / Options / ... ;
   Data uses Basic / Scope & Additional Elements / Visualizations / Analysis); each
   doc supplies whatever subset is meaningful, and exampleNotebookSlot renders only
   the present sections in this order. *)
$exampleOrder = {
    (* sectionKey normalises " & " -> " and ", so the lookup keys must
       match the normalised form (issue #12; dual of #8). *)
    "basic examples", "scope", "scope and additional elements",
    "generalizations and extensions", "options", "applications",
    "visualizations", "analysis",
    "properties and relations", "possible issues", "neat examples",
    "requirements"
}

$exampleTitle = <|
    "basic examples" -> "Basic Examples",
    "scope" -> "Scope",
    "scope and additional elements" -> "Scope & Additional Elements",
    "generalizations and extensions" -> "Generalizations & Extensions",
    "options" -> "Options",
    "applications" -> "Applications",
    "visualizations" -> "Visualizations",
    "analysis" -> "Analysis",
    "properties and relations" -> "Properties and Relations",
    "possible issues" -> "Possible Issues",
    "neat examples" -> "Neat Examples",
    "requirements" -> "Requirements"
|>

$osCanonical = <|
    "windows" -> "Windows", "mac" -> "MacOSX", "macosx" -> "MacOSX",
    "linux" -> "Unix", "unix" -> "Unix"
|>

asList[x_List] := x
asList[x_] := {x}

(* a TemplateSlot's default content, used as both the cell shape to clone and
   the fallback when the markdown supplies nothing for that slot. *)
(* An unfilled slot keeps the template's default cells; tag each with "MTNUnfilled"
   so NotebookToMarkdown can recognize untouched placeholder content (the Author
   Notes stub, the MyFunction[x,y] Tests seed) and omit it from the recovered
   markdown. The tag is stripped again the moment a slot is actually filled
   (cleanCell below), so authored content never carries it. *)
markUnfilled[v_] := v /. {
    Cell[c_, s_String, o1___, CellTags -> t_, o2___] :>
        Cell[c, s, o1, CellTags -> DeleteDuplicates @ Append[Flatten[{t}], "MTNUnfilled"], o2],
    cell : Cell[_, _String, o___] /; FreeQ[{o}, CellTags] :> Append[cell, CellTags -> {"MTNUnfilled"}]
}
slotDefault[opts_List] := markUnfilled @ FirstCase[opts, (DefaultValue -> v_) :> v, {}]

(* drop the markers that flag a cell as an unfilled template placeholder *)
cleanCell[cell_] := DeleteCases[
    cell /. (CellTags -> t_) :> (CellTags -> DeleteCases[Flatten[{t}], "DefaultContent" | "MTNUnfilled"]),
    CellID -> _,
    {1}
]

fillTextCells[opts_, text_String] := Block[{def = slotDefault[opts]},
    If[ def === {} || text === "",
        def,
        {cleanCell @ ReplacePart[First[def], 1 -> text]}
    ]
]

(* like fillTextCells, but the text keeps its inline formatting (`code` spans
   become templated InlineFormula, links become hyperlinks) by replacing the
   cell content with TextData rather than a bare string. *)
fillTextDataCells[opts_, text_String] := Block[{def = slotDefault[opts]},
    If[ def === {} || StringTrim[text] === "",
        def,
        {cleanCell @ ReplacePart[First[def], 1 -> TextData @ inlineTextData[text]]}
    ]
]

fillListCells[opts_, items_List] := Block[{def = slotDefault[opts], vals = DeleteCases[items, ""]},
    If[ def === {} || vals === {},
        def,
        Map[cleanCell @ ReplacePart[First[def], 1 -> #] &, vals]
    ]
]

(* like fillListCells, but an item may be a markdown link [label](url), rendered
   as a labeled hyperlink (the resource Check asks for labeled links, not raw
   URLs); a plain string stays as text. The ButtonBox sits directly in TextData
   (not inside BoxData) so the label stays a String literal - inside BoxData the
   front end would reparse a multi-word label into a RowBox, which the resource
   scraper's ButtonBox[_String, ...] link pattern would then miss. *)
(* the URL runs greedily to the LAST closing paren, so a URL containing parens or a
   paren-adjacent anchor - .../196_(number)#196_algorithm - stays whole (issue seen
   on save-back: the shortest match cut the link at the first ")"). *)
linkItemContent[item_String] := Block[{
    m = StringCases[StringTrim[item],
        StartOfString ~~ "[" ~~ t : Shortest[Except["]"] ..] ~~ "](" ~~ u : __ ~~ ")" ~~ EndOfString :> {t, u}, 1]
},
    If[ m === {},
        item,
        TextData[{ButtonBox[First @ First @ m, BaseStyle -> "Hyperlink", ButtonData -> {URL[Last @ First @ m], None}]}]
    ]
]

(* Every generated link cell is a copy of the SAME template default cell, so without an
   explicit CellID they share one (or, after cleanCell strips it, none). The ref-page
   scraper (ResourceSystemClient's validateHyperlinks -> itemCellContents) keys the link
   Item cells by CellID, so non-distinct IDs collapse the whole list to a single link.
   Stamp each with a stable per-item CellID (Hash of the source markdown, so rebuilds are
   idempotent) to keep every link distinct. *)
fillLinkCells[opts_, items_List] := Block[{def = slotDefault[opts], vals = DeleteCases[items, ""]},
    If[ def === {} || vals === {},
        def,
        Map[Append[cleanCell @ ReplacePart[First[def], 1 -> linkItemContent[#]], CellID -> Hash[#]] &, vals]
    ]
]

fillCheckbox[property_String, checked_List, type_String : "Function"] := {
    DefinitionNotebookClient`CheckboxesCell[<|
        "ResourceType" -> type, "Property" -> property, "Checked" -> checked
    |>]
}

(* a single whitespace-free token that reads as literal text rather than Wolfram
   code - a filesystem path / URL / dotted filename (`~/.prime/config.json`,
   `config.json`, `/usr/local/bin`, `https://x/y`) or a hyphen-joined identifier
   (`claude-opus-4-7`, `some-package`). Reparsing such a token through the front
   end tokenises its `/` `.` `~` `-` as WL operators (ReplaceAll, Dot, Subtract,
   ...), so it renders with stray operator spacing (`config . json`,
   `claude - opus - 4 - 7`). These are never meaningful bare WL, so keep them
   verbatim. A real code cell never matches: it carries whitespace or a
   call/bracket shape, not a lone operator-joined token; a genuine number
   (`3.14`, `1.5e3`) has no alphabetic extension and no interior hyphen, so it
   still reparses; and a single symbol (`Range`) has no operator at all. *)
verbatimInlineQ[s_String] := StringFreeQ[s, Whitespace] && Or[
    StringStartsQ[s, "~" | "/" | "./" | "../"],
    StringMatchQ[s, "." ~~ LetterCharacter ~~ ___],   (* dotfile: .gitignore, .prime *)
    StringContainsQ[s, "://"],
    StringContainsQ[s, "/"],
    StringMatchQ[s, (WordCharacter | "-" | "_" | ".") .. ~~ "." ~~ LetterCharacter ..],
    (* hyphen-joined word segments: a kebab identifier or model id, where the
       interior `-` would otherwise parse as Subtract *)
    StringMatchQ[s, WordCharacter .. ~~ ("-" ~~ WordCharacter ..) ..]
]

(* literal input boxes for a code string: parse it through the front end the way
   typing it would (ReparseBoxStructurePacket), so the boxes are the *code*.
   ToBoxes[Defer[...]] instead *renders* display heads (Framed, Style, Grid, Row,
   RGBColor, ...) into frames/swatches, corrupting the Input cell. Fall back to
   the Defer parse, then the raw string, if the front end is unavailable. *)
(* the four inert box-structure tokens of linear syntax (the ASCII form
   NotebookToMarkdown emits) mapped to the active PUA codes the front end writes
   when content is typeset (issue #35); ReparseBoxStructurePacket does not
   reactivate them inside a string literal, so a typeset PlotLabel / ket label
   would otherwise rebuild as literal ASCII instead of a subscript. *)
$linearSyntaxReactivate = {
    "\\!" -> FromCharacterCode[63425], "\\(" -> FromCharacterCode[63433],
    "\\*" -> FromCharacterCode[63432], "\\)" -> FromCharacterCode[63424]};
(* the inert linear-syntax group opener (backslash-bang backslash-paren), assembled
   from pieces so the converter's own source carries no literal run of it to
   self-match. Every group opens with this regardless of what follows - "\*<box>",
   a form tag ("TraditionalForm`..."), or a bare group - so gating on it catches all
   three (issue #57), not just the star-box shape. *)
$linearSyntaxLeadIn = StringJoin["\\", "!", "\\", "("];
(* a cell whose ENTIRE source is one string literal carrying that inert lead-in is
   a typeset string label (a PlotLabel, a ket, a TableHeadings entry). Reactivation
   is restricted to such a whole-string-literal cell, so ordinary code that merely
   mentions the tokens - including this converter's own source and its tests - is
   never rewritten. *)
stringLabelQ[s_String] := StringStartsQ[s, "\""] && StringEndsQ[s, "\""] &&
    StringContainsQ[s, $linearSyntaxLeadIn]

inputBoxes[code_String] := Block[{boxes, parsed, trimmed = StringTrim[code]},
    If[ stringLabelQ[trimmed],
        (* a typeset string label is WL box syntax, not LaTeX: reactivate its inert
           tokens so it renders, and skip the guards below (its own escaped newline
           must not trip the LaTeX guard). *)
        trimmed = StringReplace[trimmed, $linearSyntaxReactivate],
        (* LaTeX-style "\command" sequences (\left, \right, \sqrt, \to, \notin, ...)
           collide with Wolfram's string-escape syntax: the front end's reparser
           interprets "\r" / "\n" / "\t" / "\b" / "\f" as their control-character
           escapes, so "\right" gets tokenised as "\r" + "ight". For inputs
           containing backslash + two-or-more-letter commands - never valid bare
           WL, but the normal shape of inline LaTeX - skip the reparse and emit the
           raw string so it renders verbatim. "\[Name]" Wolfram named characters
           are unaffected because they have "[" (not a letter) after the backslash. *)
        (* exempt a cell that carries linear syntax: its lead-in followed by a letter
           (e.g. the newline before "SubscriptBox" in a multiline box) is WL box code,
           not LaTeX, and must reach the reparse + reactivation below (issue #58). *)
        If[StringContainsQ[trimmed, "\\" ~~ LetterCharacter ~~ LetterCharacter] &&
            ! StringContainsQ[trimmed, $linearSyntaxLeadIn],
            Return[trimmed]
        ];
        (* a path / URL / dotted filename: keep verbatim (see verbatimInlineQ). *)
        If[verbatimInlineQ[trimmed], Return[trimmed]]
    ];
    boxes = Quiet @ UsingFrontEnd @ MathLink`CallFrontEnd[FrontEnd`ReparseBoxStructurePacket[trimmed]];
    If[ FreeQ[boxes, $Failed] && (StringQ[boxes] || ! AtomQ[boxes]),
        reactivateStringLinearSyntax @ fixBlankHead[boxes],
        parsed = Quiet @ ToExpression[code, StandardForm, Defer];
        If[parsed === $Failed, code, ToBoxes[parsed]]
    ]
]

(* ReparseBoxStructurePacket does not reactivate linear syntax inside a string
   literal it does not own (a nested "..." argument, e.g. an AssociationThread key),
   so a box-syntax string one argument deep rebuilds as literal ASCII. Walk the
   reparsed boxes and reactivate the inert tokens in every String box token that
   carries the full lead-in - keyed on the complete opener so a token holding a stray
   group-open is untouched (issue #44). A no-op on the whole-string-label path, where
   the token was already reactivated before the reparse. *)
reactivateStringLinearSyntax[boxes_] := boxes /.
    s_String /; StringContainsQ[s, $linearSyntaxLeadIn] :> StringReplace[s, $linearSyntaxReactivate]

(* The FE reparser splits a Blank from a NAMED-character head: an underscore
   followed by a Wolfram named character comes back as a 2-element RowBox meaning
   Times[Blank[], head] (matches nothing), even though an ASCII head stays joined
   (issue #39). A genuine Times[Blank[], h] keeps its space (a 3-element RowBox),
   so a 2-element split is the broken Blank-with-head: re-join it into one leaf,
   which parses as Blank[head]. *)
fixBlankHead[boxes_] := boxes /.
    RowBox[{"_", h_String /; StringLength[h] == 1 && StringMatchQ[h, LetterCharacter]}] :> "_" <> h

(* extra options for an example's Output cell, from the code cell's "#|" options.
   "#| background: papertear" sets BackgroundAppearance -> "PaperTear", the cell
   option the front end's Convert To > Paper Tear menu item toggles - a torn-paper
   edge, used to make a generated-notebook screenshot look like a screenshot. *)
(* "#| tear: ..." gives an output cell the front end's torn-paper appearance. The
   tear only shows once the cell is height-constrained, so it also sets a CellSize:
   "#| tear: h" keeps the top h points visible (smaller tears more off), while
   "#| tear: true" (or yes / auto) uses a default height. "#| tear: false" (or no
   tear option) leaves the output untorn. *)
$defaultTearHeight = 200

paperTearQ[block_] := Lookup[block["Options"], "tear", False] =!= False

tearHeight[block_] := With[{v = Lookup[block["Options"], "tear", True]},
    Which[
        NumberQ[v], v,
        StringQ[v] && NumberQ[Quiet @ ToExpression[v]], ToExpression[v],
        True, $defaultTearHeight
    ]
]

extraOutputOpts[block_] := If[
    paperTearQ[block],
    {BackgroundAppearance -> "PaperTear", CellSize -> {Automatic, tearHeight[block]}},
    {}
]

(* hideInput drops the Input cell entirely and emits only the captured Output
   (plus any messages). The use case is a Demonstration Snapshot: the cell's
   code recreates the Manipulate at a specific control state via a parameterised
   helper from the Initialization section ("demo[p1, p2]"), but only the
   resulting panel image is wanted in the published notebook - showing the
   call would clutter the snapshot section. Toggled per-cell with
   "#| input: false". *)
exampleIO[code_String, outBoxes_, n_Integer, outOpts_List : {}, msgs_List : {}, hideInput : (True | False) : False, prints_List : {}, extraCells_List : {}, outsList_List : Automatic] := Block[{
    inCell = Cell[BoxData[inputBoxes[code]], "Input", CellLabel -> "In[" <> ToString[n] <> "]:= "],
    printCells = asPrintCell /@ prints,
    msgCells = messageCell /@ msgs,
    outputCells, allOuts
},
    (* prefer the explicit per-statement outs list when given; fall back to
       the single OutputBoxes for legacy callers. A "No useful output" cell
       (Missing[] / Null entry) is dropped so a Cell whose only statements
       are `;`-suppressed renders cleanly as input + prints. *)
    allOuts = If[ListQ[outsList] && outsList =!= {Automatic} && outsList =!= Automatic,
        outsList, {outBoxes}];
    allOuts = DeleteCases[allOuts, _?MissingQ | Null];
    outputCells = MapIndexed[
        With[{label = If[hideInput, Nothing, CellLabel -> "Out[" <> ToString[n] <> If[Length[allOuts] > 1, "@" <> ToString[First[#2]], ""] <> "]= "]},
            Cell[BoxData[#1], "Output", label, Sequence @@ outOpts]] &,
        allOuts];
    Which[
        outputCells === {},
            If[hideInput, Flatten[{extraCells, printCells, msgCells}],
               Flatten[{inCell, extraCells, printCells, msgCells}]],
        hideInput,
            Flatten[{extraCells, printCells, msgCells, outputCells}],
        True,
            {Cell[CellGroupData[Flatten[{inCell, extraCells, printCells, msgCells, outputCells}], Open]]}
    ]
]

(* a documentation *flag* - the front end's Futurize / Excise / ... toolbar
   buttons, which mark a page or cell for the doc build (DocumentationBuild reads
   these flag-styled banner cells to include, hide, or defer content). A
   document-level flag is the "Flag" frontmatter key; a per-cell flag is a code
   cell's "#| flag: ..." option. The value is a friendly name mapped to the build's
   flag cell style and its spaced-out banner text. *)
$flagStyles = <|
    "future" -> "FutureFlag", "futurize" -> "FutureFlag",
    "excised" -> "ExcisedFlag", "excise" -> "ExcisedFlag",
    "obsolete" -> "ObsoleteFlag",
    "temporary" -> "TemporaryFlag",
    "preview" -> "PreviewFlag",
    "internal" -> "InternalFlag"
|>
$flagBanners = <|
    "FutureFlag" -> "F  U  T  U  R  E",
    "ExcisedFlag" -> "E  X  C  I  S  E  D",
    "ObsoleteFlag" -> "O  B  S  O  L  E  T  E",
    "TemporaryFlag" -> "T  E  M  P  O  R  A  R  Y",
    "PreviewFlag" -> "P  R  E  V  I  E  W",
    "InternalFlag" -> "I  N  T  E  R  N  A  L"
|>
flagCell[v_String] := With[{s = Lookup[$flagStyles, ToLowerCase[StringTrim[v]], None]},
    If[s === None, Nothing, Cell[$flagBanners[s], s]]]
flagCell[_] := Nothing

(* prefix a list of cells with the block's per-cell flag banner ("#| flag: ...") *)
withCellFlag[block_, cells_List] := With[{f = flagCell[Lookup[block["Options"], "flag", ""]]},
    If[f === Nothing, cells, Prepend[cells, f]]]

(* "#| excluded: true" appends the "Excluded" cell style. The resource scraper
   strips any Cell[..., "Excluded", ...] from the published resource (vExclusions
   in ResourceSystemClient`DefinitionNotebook`Scraping`), but the cell stays in
   the source .nb so the author can keep work-in-progress or reviewer notes that
   travel with the document but never ship.

   Split a Cell's args into "leading style strings" and "trailing options"
   manually - the `Cell[content_, styles___String, opts___]` pattern doesn't
   bind styles greedily (___String prefers a zero match when followed by ___),
   so we'd end up emitting Cell[content, "Excluded", "Input", ...] with the
   modifier style ahead of the base. *)
splitCellArgs[args_List] := Block[{styles, rest},
    styles = TakeWhile[args, StringQ];
    rest = Drop[args, Length[styles]];
    {styles, rest}
]

withExtraCellStyle[Cell[CellGroupData[cells_List, st_], go___], style_String] :=
    Cell[CellGroupData[Map[withExtraCellStyle[#, style] &, cells], st], go]
withExtraCellStyle[Cell[content_, args___], style_String] := Block[
    {parts = splitCellArgs[{args}]},
    Cell[content, Sequence @@ parts[[1]], style, Sequence @@ parts[[2]]]
]
withExtraCellStyle[other_, _] := other

applyExcluded[block_, cells_List] := If[
    TrueQ[Lookup[block["Options"], "excluded", False]],
    Map[withExtraCellStyle[#, "Excluded"] &, cells],
    cells
]

(* "#| hidden: true" closes the cell on the *published* web page but keeps it
   open in the downloadable example notebook - that is, CellOpen -> False plus
   the "HiddenMaterial" modifier style (which the FunctionResource stylesheet
   wraps in a green-edged frame with a "hidden" label so the author sees it
   is marked). The cell still scrapes into the deployed resource, unlike
   "excluded" which strips it entirely. *)
withHiddenOptions[Cell[CellGroupData[cells_List, _], go___]] :=
    Cell[CellGroupData[Map[withHiddenOptions, cells], Closed], go]
withHiddenOptions[Cell[content_, args___]] := Block[
    {parts = splitCellArgs[{args}]},
    Cell[content, Sequence @@ parts[[1]], "HiddenMaterial",
         Sequence @@ parts[[2]], CellOpen -> False]
]
withHiddenOptions[other_] := other

applyHidden[block_, cells_List] := If[
    TrueQ[Lookup[block["Options"], "hidden", False]],
    Map[withHiddenOptions, cells],
    cells
]

(* "#| collapse: input"  ("true" alias) - hide the example's Input cell,
   keep Output visible. Implemented as CellGroupData[..., {n,...}] where
   the int-list second arg picks which cells stay visible by 1-based index;
   the group bracket reveals the hidden cells when clicked.
   "#| collapse: output" - keep Input visible, hide Output. CellGroupData
   defaults to showing its first cell when Closed, and the example's first
   cell IS the Input, so we just set the group state to Closed.
   "#| collapse: all"    - hide BOTH. CellOpen -> False on each cell of the
   example's group; the group bracket on the right stays clickable. *)
collapseMode[v_] := Switch[v,
    True | "true" | "input" | "Input", "Input",
    "output" | "Output", "Output",
    "all" | "All" | "both" | "Both", "All",
    _, None
]

(* recurse into nested CellGroupData; at the example group, apply the requested
   collapse and stop. *)
applyCollapseMode[mode_String][Cell[CellGroupData[cells_List, state_], go___]] :=
    Switch[mode,
        "Input",
            (* hide Input - show only the indices of the non-Input cells *)
            With[{visible = Flatten @ Position[cells, Cell[_, s_String, ___] /; s =!= "Input", {1}, Heads -> False]},
                If[visible === {}, Cell[CellGroupData[cells, state], go],
                    Cell[CellGroupData[cells, visible], go]
                ]
            ],
        "Output",
            (* default Closed shows only the first cell (Input); good as-is *)
            Cell[CellGroupData[cells, Closed], go],
        "All",
            (* hide everything - CellOpen -> False per cell, group bracket stays *)
            Cell[CellGroupData[closeCell /@ cells, state], go]
    ]
applyCollapseMode[_][other_] := other

closeCell[Cell[content_, style___, opts:OptionsPattern[]]] :=
    If[FreeQ[{opts}, CellOpen], Cell[content, style, opts, CellOpen -> False], Cell[content, style, opts]]
closeCell[other_] := other

applyCollapse[block_, cells_List] := With[{mode = collapseMode[Lookup[block["Options"], "collapse", False]]},
    If[mode === None, cells, applyCollapseMode[mode] /@ cells]
]

(* an example's cells (Input / Output), prefixed with its per-cell flag banner
   and decorated with any "excluded" / "hidden" per-cell tag. "#| input: false"
   drops the Input cell - the example renders as just its captured Output (the
   Demonstration-snapshot use case). *)
(* a "#| screenshot: true" cell keeps its directive in the notebook as an
   "MTNScreenshot" cell tag on the Input, so NotebookToMarkdown can re-emit the
   directive on the way back (the rasterized twin output itself carries no trace). *)
withScreenshotMark[block_, cells_List] := If[
    TrueQ[Lookup[block["Options"], "screenshot", False]],
    cells /. Cell[c_, "Input", o___] /; FreeQ[{o}, CellTags] :>
        Cell[c, "Input", o, CellTags -> {"MTNScreenshot"}],
    cells
]
exampleIOFor[block_, n_Integer] :=
    applyExcluded[block, applyHidden[block, applyCollapse[block, withCellFlag[block, withScreenshotMark[block, exampleIO[
        block["Code"], block["OutputBoxes"], n,
        extraOutputOpts[block], Lookup[block, "Messages", {}],
        Lookup[block["Options"], "input", True] === False,
        Lookup[block, "Prints", {}],
        Lookup[block, "ExtraCells", {}],
        Lookup[block, "Outputs", Automatic]
    ]]]]]]

(* a document-level flag banner ("Flag" frontmatter) prepended to the notebook *)
applyDocFlag[nb_, ""] := nb
applyDocFlag[Notebook[cells_, o___], v_String] := With[{f = flagCell[v]},
    If[f === Nothing, Notebook[cells, o], Notebook[Prepend[cells, f], o]]]
applyDocFlag[nb_, _] := nb

(* the filled function-definition cells. The code cell must carry the
   "DefaultContent" cell tag the official template puts on every content cell, or
   the resource scraper (and the submission Check) does not recognize it as the
   function's definition. Any prose the author wrote in the "## Definition" section
   is kept as Text cells ahead of the code so it survives the notebook round-trip. *)
functionSlot[opts_, defCode_String, sections_ : <||>] := Block[
    {proseCells = proseBlockCells[Cases[Lookup[sections, "definition", {}], b_ /; b["Type"] === "Prose"]],
     codeCells},
    codeCells = If[defCode === "", {},
        {Cell[BoxData[defCode], "Code", CellTags -> {"DefaultContent"}, InitializationCell -> True]}];
    If[proseCells === {} && codeCells === {}, slotDefault[opts], Join[proseCells, codeCells]]
]

(* the content-defining cells of an Example Repository resource (the "ContentElements"
   slot). An Example resource exposes named content via ResourceData, so each
   executable cell in a "## Content" section is the literal defining assignment
   (typically ResourceData[ResourceObject[EvaluationNotebook[]], "name"] = value) and
   becomes an Input cell carrying the "DefaultContent" tag the scraper needs. *)
codeBlockQ[b_] := b["Type"] === "Code" && MemberQ[{"wl", "wolfram", "mathematica"}, b["Lang"]]

contentSlot[opts_, sections_] := Block[{cells = Cases[Lookup[sections, "content", {}], b_ /; codeBlockQ[b]]},
    If[ cells === {},
        slotDefault[opts],
        Map[contentCell, cells]
    ]
]

(* A "#| init: true" content cell becomes a collapsed initialization Code cell -
   mirroring the FunctionResource definition cell - so a long primary-data
   assignment (e.g. a big Uncompress[...] payload) initializes on open without
   showing a wall of source in the deployed notebook. Every other content cell
   stays a visible Input. Both carry the "DefaultContent" tag the scraper needs. *)
contentCell[b_] := If[
    TrueQ[Lookup[b["Options"], "init", False]],
    Cell[BoxData[inputBoxes[b["Code"]]], "Code",
        CellTags -> {"DefaultContent"}, InitializationCell -> True, CellOpen -> False],
    Cell[BoxData[inputBoxes[b["Code"]]], "Input", CellTags -> {"DefaultContent"}]
]

(* === single-cell-from-section helpers, used by Prompt and Demonstration ===
   Each fills a TemplateSlot with one cell built from the FIRST code block (or
   prose block) of a given markdown section. They mirror contentSlot's pattern
   but for slots that take a single value rather than a list, and tag the cell
   with "DefaultContent" so the resource scraper picks it up. *)

(* Pull the first executable WL block from a section, or Missing[] if none. *)
firstCodeOf[sections_, key_] := FirstCase[Lookup[sections, key, {}], b_ /; codeBlockQ[b], Missing[]]

(* All executable WL blocks in a section, in order. *)
allCodeOf[sections_, key_] := Cases[Lookup[sections, key, {}], b_ /; codeBlockQ[b]]

(* Cell metadata carried by a block's #| directives (attachDirectives put them in
   "Options"): "#| style: S" overrides the cell's inferred style, "#| tags: a, b"
   sets CellTags. Applied to each cell a block produces, so a non-standard styled
   or tagged cell round-trips (NotebookToMarkdown re-emits these directives). *)
cellTagList[v_] := DeleteCases[StringTrim /@ StringSplit[ToString[v], ","], ""]

(* The "LastAnnotator" name baked into the annotation chrome. DocumentationTools'
   AnnotationCell[] uses $AuthorUserName - the FrontEnd "AuthorUserName" interface
   setting, else $UserName. For a headless / cloud build we prefer $CloudAccountName
   (the publishing account), falling back to $UserName when not cloud-connected.
   Resolved at build time, as DocumentationTools does, so the note records who
   generated it. *)
annotatorName[] := With[{n = $CloudAccountName}, If[StringQ[n] && n =!= "", n, $UserName]]

(* the Edit / annotator / Delete chrome DocumentationTools' AnnotationRemove /
   AnnotationSearch match against ($AnnotationCellPattern); rebuilt verbatim so a
   round-tripped "#| annotation:" stays a real, removable annotation. Self-
   contained box literals - no DocumentationTools dependency. The "LastAnnotator"
   slot carries annotatorName[], matching AnnotationCell[]'s RowBox[{label, name}]. *)
annotationButtonsCell[] := With[{author = annotatorName[]}, Cell[BoxData[GridBox[
    {{
        Cell[BoxData[ButtonBox[DynamicBox[FEPrivate`FrontEndResource["DocumentationToolsStrings", "Edit"]],
            BaseStyle -> "TextAnnotationButton"]]],
        StyleBox[RowBox[{DynamicBox[FEPrivate`FrontEndResource["DocumentationToolsStrings", "LastAnnotator"]], author}],
            "TextAnnotator"],
        Cell[BoxData[ButtonBox[DynamicBox[FEPrivate`FrontEndResource["DocumentationToolsStrings", "Delete"]],
            BaseStyle -> "TextAnnotationRemoveButton"]]],
        ""
    }},
    GridBoxAlignment -> {"Columns" -> {Left, Left, Right, Right}, "Rows" -> {{Automatic}}},
    GridBoxItemSize -> {"Columns" -> {Scaled[0.15], Scaled[0.68], Scaled[0.15], Scaled[0.02]}}]]]]

(* the CellFrameLabels an "Annotate" annotation lives in: the note (its date
   prefix kept verbatim from the directive) over the Edit/Delete chrome. *)
annotationFrameLabels[note_String] := CellFrameLabels -> {{Inherited, Inherited}, {Inherited,
    Cell[TextData[{note, "\n\n", annotationButtonsCell[], "\n"}], "TextAnnotation", CellSize -> {590, Inherited}]}}

(* An annotated cell needs a present, unique CellID: GenerateAnnotationDialog
   (the Edit button) reads it and NotebookFind locates the cell by that value.
   That CellID is supplied deterministically by withDeterministicIDs when the
   notebook is finalized - from the cell's structural position, so it is unique
   and stable across rebuilds (a content-derived hash would collide for two cells
   with the same body + note) - so nothing needs to be stamped here. *)

(* Idempotent: re-applying the same options is a no-op (existing CellTags are
   replaced, not duplicated), so a cell may pass through applyCellMeta more than
   once - e.g. nonExecutableCell metas an Output block, then a wrapping builder
   metas it again. *)
applyCellMeta[Cell[c_, st_String, rest___], opts_Association] := Module[{r = {rest}, tags},
    tags = If[KeyExistsQ[opts, "tags"], cellTagList[opts["tags"]], {}];
    (* an annotation also carries the "TextAnnotation" CellTag that marks the cell *)
    If[KeyExistsQ[opts, "annotation"], tags = Append[tags, "TextAnnotation"]];
    If[KeyExistsQ[opts, "tags"] || KeyExistsQ[opts, "annotation"],
        r = Append[DeleteCases[r, CellTags -> _], CellTags -> DeleteDuplicates[tags]]];
    If[KeyExistsQ[opts, "annotation"],
        r = Append[DeleteCases[r, CellFrameLabels -> _], annotationFrameLabels[opts["annotation"]]]];
    Cell[c, Lookup[opts, "style", st], Sequence @@ r]
]
(* an evaluated code cell is wrapped as Cell[CellGroupData[{Input, Output}, ...]];
   apply the block's #| style / tags / annotation to the FIRST (Input) cell inside -
   the one the directive belongs on - so a code cell's tag / annotation round-trips
   (issue #42), not just an unevaluated (bare Input) one. *)
applyCellMeta[Cell[CellGroupData[{first_, rest___}, gopts___], copts___], opts_Association] :=
    Cell[CellGroupData[{applyCellMeta[first, opts], rest}, gopts], copts]
applyCellMeta[other_, _] := other

applyBlockMeta[cells_List, b_] := Module[{o = Lookup[b, "Options", <||>], hm, out},
    hm = Lookup[o, "headingMeta", <||>];
    (* the block's OWN style / tags / annotation apply to every cell it produces *)
    out = If[KeyExistsQ[o, "style"] || KeyExistsQ[o, "tags"] || KeyExistsQ[o, "annotation"],
        applyCellMeta[#, o] & /@ cells, cells];
    (* a directive inherited from the section heading annotates the first cell only *)
    If[hm =!= <||> && out =!= {}, out = MapAt[applyCellMeta[#, hm] &, out, 1]];
    out]

(* All prose / list / quote / table blocks of a section, in order, as ordinary
   Text cells - the format the Demonstration template's Caption / Details /
   References slots expect. *)
proseBlockCells[blocks_, style_String : "Text"] := Catenate @ Map[
    b |-> applyBlockMeta[Switch[b["Type"],
        "Prose", {Cell[TextData @ inlineTextData[b["Text"]], style]},
        "List",  listItemCells[b, style],
        "Table", {tableCell[b]},
        "Quote", {quoteCell[b["Text"]]},
        "MathBlock", {mathBlockCell[b["Text"]]},
        _, {}
    ], b],
    blocks
]

(* Fill a slot with a single Input cell built from the first code block of the
   named section; falls back to the template default if the section is empty.
   The cell carries "DefaultContent" so the official scraper finds it. *)
codeSlot[opts_, sections_, key_String] := Block[{b = firstCodeOf[sections, key]},
    If[ MissingQ[b],
        slotDefault[opts],
        {Cell[BoxData[inputBoxes[b["Code"]]], "Input", CellTags -> {"DefaultContent"}]}
    ]
]

(* Fill a slot with one Input cell per code block of the named section. Used for
   Snapshot groups (>= 3 panel-producing inputs) and similar list-of-cells
   slots. A cell flagged "#| input: false" emits only its captured Output (no
   Input cell, no In[]/Out[] label) - the Demonstration snapshot convention:
   the snapshot is the *rendered Manipulate panel* at a parameter state,
   produced by calling a helper from the Initialization section, with only
   the panel visible. *)
multiCodeSlot[opts_, sections_, key_String] := Block[{cells = allCodeOf[sections, key]},
    If[ cells === {}, Return[slotDefault[opts]] ];
    Catenate @ MapIndexed[
        Function[{b, ix},
            If[ Lookup[b["Options"], "input", True] === False,
                Block[{out = Lookup[b, "OutputBoxes", Missing[]]},
                    If[MissingQ[out] || out === Null, {}, {Cell[BoxData[out], "Output", CellTags -> {"DefaultContent"}]}]
                ],
                {Cell[BoxData[inputBoxes[b["Code"]]], "Input", CellTags -> {"DefaultContent"}]}
            ]
        ],
        cells
    ]
]

(* Fill a slot with one Text (or other styled) cell per prose / list / quote
   block of the named section. Used for CaptionCells / DetailCells /
   ReferenceCells in the Demonstration template, and PromptTemplate in the
   Prompt template (whose body is plain prose). *)
proseSectionSlot[opts_, sections_, key_String, style_String : "Text"] := Block[{cells},
    cells = proseBlockCells[Lookup[sections, key, {}], style];
    If[cells === {}, slotDefault[opts], cells]
]

(* A Manipulate slot needs the Input cell AND its evaluated Manipulate output
   (the live panel), grouped so the published demo shows the panel. The cached
   OutputBoxes from the example-evaluation pass provide the output; without it
   we leave the Input alone and let the front end produce the output on open. *)
manipulateSlot[opts_, sections_] := Block[{b = firstCodeOf[sections, "manipulate"]},
    If[ MissingQ[b], Return[slotDefault[opts]] ];
    Block[{out = Lookup[b, "OutputBoxes", Missing[]]},
        If[ MissingQ[out] || out === Null,
            {Cell[BoxData[inputBoxes[b["Code"]]], "Input", CellTags -> {"DefaultContent"}]},
            {Cell[CellGroupData[{
                Cell[BoxData[inputBoxes[b["Code"]]], "Input", CellTags -> {"DefaultContent"}],
                Cell[BoxData[out], "Output"]
            }, Open]]}
        ]
    ]
]

(* a Usage section is a sequence of usage statements, one per prose paragraph
   that begins with a `code` span: the code is the signature (e.g.
   `MarkdownToNotebook[source]`) and the rest is its description. The signature
   is templated like the "Template Input" button (arguments italic, head linked)
   and the description keeps its inline formatting. *)
(* a usage statement is either a backticked code-span signature (legacy form,
   `Name[c$1, c$2]`) or a prose signature with inline-math arguments (the
   pandoc-friendly form, "Name[$c_1$, $c_2$]"). The math form renders correctly
   in pandoc / GitHub since markdown forbids nested formatting inside code spans;
   for our notebook output, "$c_1$" is rewritten to the ParseTextTemplate
   subscript form "c$1" and fed through templateBox. *)
mathArgsToTemplate[s_String] := StringReplace[s, {
    "$" ~~ base:(LetterCharacter ~~ (WordCharacter ...)) ~~ "_" ~~ "{" ~~ sub:Shortest[Except["}"]..] ~~ "}" ~~ "$" :> base <> "$" <> sub,
    "$" ~~ base:(LetterCharacter ~~ (WordCharacter ...)) ~~ "_" ~~ sub:(DigitCharacter | LetterCharacter) ~~ "$" :> base <> "$" <> ToString[sub],
    "$" ~~ ident:(LetterCharacter ~~ (WordCharacter ...)) ~~ "$" :> ident
}]

(* Sanitize the markdown styling out of a usage signature, leaving the plain WL
   signature string that templateBox / ParseTextTemplate can render. Strips
   inferred-link wrappers in both forms - the canonical bare "[Name](url)" and
   the legacy backtick-wrapped "[`Name`](url)" - and "*italic*" markers. The
   "$x_i$" math and "<sub>i</sub>" / "~i~" subscript forms pass through to
   mathArgsToTemplate / mdToTemplateSubs which already know how to template
   them. The backticked rule runs first so a "[`X`](url)" does not part-match
   the bare rule and leak its surrounding backticks. *)
unwrapMarkdownSig[s_String] := StringReplace[s, {
    (* WL-identifier shape only: leading letter / "$", then word chars /
       "$" / context backticks.  Restricting the label keeps the unwrap
       from over-matching across WL bracket syntax (e.g.
       <code>[Function]()[x, [Exp]() @ x]</code> - the outer [x, ...]
       must not be eaten as if it were a markdown link with label "x, [Exp"). *)
    "[`" ~~ n : ((LetterCharacter | "$") ~~ (WordCharacter | "$" | "`") ...) ~~ "`](" ~~ Shortest[Except[")"] ...] ~~ ")" :> n,
    "[" ~~ n : ((LetterCharacter | "$") ~~ (WordCharacter | "$" | "`") ...) ~~ "](" ~~ Shortest[Except[")"] ...] ~~ ")" :> n,
    (* strip the *...* italic markers around an argument - ParseTextTemplate
       italicises the args itself, so a leftover "*" only renders as literal
       text. Allow spaces inside so a multi-token arg (*{x1, ..., xn}*) is
       stripped too, not just a single word. *)
    "*" ~~ w : Shortest[Except["*"] ..] ~~ "*" :> w
}]

usageStatement[text_String] := Block[{trimmed = StringTrim[text], m},
    (* the canonical wrapper: <code>...</code>. GitHub / Pandoc process markdown
       *inside* an inline HTML tag, so the inferred-link head, italic args, math
       subscripts, etc. all render naturally while the whole span is code-styled.
       Strip the code wrapper and the inner markdown to recover the plain WL
       signature; the templateBox / ParseTextTemplate pipeline does the rest. *)
    m = StringCases[trimmed,
        StartOfString ~~ "<code>" ~~ sig : Shortest[__] ~~ "</code>" ~~ rest___ :>
            {mathArgsToTemplate[unwrapMarkdownSig[sig]], StringTrim[rest]}, 1];
    If[m =!= {}, Return[m]];
    (* hybrid form (pandoc-friendly): a backticked head followed *immediately* by a
       "[...]" bracket group whose args use inline math. *)
    m = StringCases[trimmed,
        StartOfString ~~ "`" ~~ name : Shortest[Except["`"] ..] ~~ "`" ~~ args : ("[" ~~ Shortest[Except["\n"] ..] ~~ "]") ~~ rest___ :>
            {name <> mathArgsToTemplate[args], StringTrim[rest]}, 1];
    If[m =!= {}, Return[m]];
    (* legacy form: the whole signature inside one code span ("`f[x~1~, x~2~]`"). *)
    m = StringCases[trimmed,
        StartOfString ~~ "`" ~~ c : Shortest[__] ~~ "`" ~~ rest___ :> {c, StringTrim[rest]}, 1];
    If[m =!= {}, Return[m]];
    (* inferred-link head form: "[Head]()[args] prose" / "[Head](url)[args] prose"
       - the head is a markdown link (auto-linked symbol) immediately followed by
       the bracketed arguments. The line starts with "[", so the prose form below
       (which needs a letter head) never catches it. *)
    m = StringCases[trimmed,
        StartOfString ~~ sig : ("[" ~~ ((LetterCharacter | "$") ~~ (WordCharacter | "$" | "`") ...) ~~
            "](" ~~ Shortest[Except[")"] ...] ~~ ")" ~~ "[" ~~ Shortest[Except["\n"] ..] ~~ "]") ~~ rest___ :>
            {mathArgsToTemplate[unwrapMarkdownSig[sig]], StringTrim[rest]}, 1];
    If[m =!= {}, Return[m]];
    (* italic-head form: "*m*[args] prose" - an object-instance line whose head is
       an italic variable rather than a symbol (e.g. *m*["prop"]). *)
    m = StringCases[trimmed,
        StartOfString ~~ sig : ("*" ~~ Shortest[Except["*"] ..] ~~ "*" ~~
            "[" ~~ Shortest[Except["\n"] ..] ~~ "]") ~~ rest___ :>
            {mathArgsToTemplate[unwrapMarkdownSig[sig]], StringTrim[rest]}, 1];
    If[m =!= {}, Return[m]];
    (* prose form: an identifier head, then [ ... ] balanced once, then prose. *)
    StringCases[trimmed,
        StartOfString ~~ name : (LetterCharacter ~~ (WordCharacter | "`") ...) ~~ args : ("[" ~~ Shortest[Except["\n"] ..] ~~ "]") ~~ rest___ :>
            {name <> mathArgsToTemplate[args], StringTrim[rest]},
        1]
]

(* one usage line as inline TextData items: ModInfo placeholder + the
   InlineFormula signature + the prose description. The signature goes through
   codeInlineCell (the <code>...</code> handler) so the head gets its
   paclet-ref ButtonBox link while ParseTextTemplate's auto-linking of
   incidental System symbols inside the args is stripped.

   The separator between the signature and its description is
   \[LineSeparator] (U+2028, a soft line break) - NOT a plain space. This is
   what the palette's "Double Usage Line" template inserts
   (TextData[{Cell[..,"ModInfo"], Cell[..,"InlineFormula"],
   "\[LineSeparator]XXXX", "\n"}]) and is exactly why the style is "double":
   the description wraps onto its own line below the code. Plain "\n" is
   reserved for separating distinct usage statements (see usageMultiCell). *)
usageLineItems[{code_String, desc_String}] := Block[{trimmedDesc = StringTrim[desc]},
    Join[
        {Cell["   ", "ModInfo"], codeInlineCell[code]},
        If[trimmedDesc === "", {}, Prepend[inlineTextData[trimmedDesc], "\[LineSeparator]"]]
    ]
]
(* a free prose paragraph in "## Usage" (no leading signature): keep it as its own
   line of the Usage cell rather than dropping it *)
usageLineItems[{None, text_String}] := inlineTextData[StringTrim[text]]

(* every "## Usage" prose paragraph as a {signature, description} pair; one that
   parses to no signature is kept as a free {None, text} line instead of vanishing *)
usageLines[sections_] := Flatten[
    Map[
        Function[t, Replace[usageStatement[t], {} :> {{None, t}}]],
        Cases[Lookup[sections, "usage", {}], b_ /; b["Type"] === "Prose" :> b["Text"]]
    ],
    1
]

(* the palette's "Double Usage Line" template inserts ONE `Cell[..., "Usage"]`
   whose TextData lists every usage line in the section, separated by
   newlines. So N "## Usage" paragraphs in markdown collapse into one Usage
   cell with N lines inside - matching what DoubleUsageLinesInsert writes.
   Used by the Symbol template's symbolNotebook. The FunctionResource
   template uses usagePair instead - the WFR resource scraper expects the
   UsageInputs / UsageDescription pair structure and rejects a single-cell
   Usage shape. *)
usageMultiCell[pairs_List] := Cell[
    TextData @ Flatten @ Riffle[usageLineItems /@ pairs, {"\n"}],
    "Usage"
]

(* one usage line as the pair of cells the WFR FunctionResource scraper
   expects: a UsageInputs cell holding the signature boxes, followed by a
   UsageDescription cell holding the prose. The two stack as one visual
   usage line in the resource page; multiple pairs catenate into one
   CellGroupData. *)
usagePair[{code_String, desc_String}] := {
    Cell[BoxData[stripLinks @ templateBox[code]], "UsageInputs", FontFamily -> "Source Sans Pro"],
    Cell[TextData @ inlineTextData[desc], "UsageDescription"]
}
(* a free usage paragraph: description-only, no UsageInputs partner *)
usagePair[{None, text_String}] := {Cell[TextData @ inlineTextData[StringTrim[text]], "UsageDescription"]}

usageSlot[opts_, sections_] := Block[{pairs = usageLines[sections]},
    If[ pairs === {}, Return[slotDefault[opts]] ];
    {Cell[CellGroupData[Catenate[usagePair /@ pairs], Open]]}
]

(* the Details & Options notes: one "Notes" cell per item, so each renders as its
   own bullet (the reference-page convention) - a paragraph is one note, a markdown
   list is one note per item, a table becomes a grid. *)
(* a blockquote -> a Text cell set off by a left rule and indent, the way GitHub
   renders "> ...". Self-styled (CellFrame / CellMargins), so it does not depend on
   a Quote cell style being present in the template's stylesheet. *)
quoteCell[text_String] := Cell[TextData @ inlineTextData[text], "Text",
    FontSlant -> "Italic", FontColor -> LightDarkSwitched[GrayLevel[0.45], GrayLevel[0.65]],
    CellFrame -> {{3, 0}, {0, 0}}, CellFrameColor -> GrayLevel[0.55], CellFrameMargins -> 10,
    CellMargins -> {{40, 10}, {7, 7}},
    Background -> LightDarkSwitched[GrayLevel[0.96], GrayLevel[0.2]]]

(* the nested-bullet style ladder for each base style: an indented sub-bullet
   steps to the next entry (Item -> Subitem -> Subsubitem, the doc-stylesheet
   names). A base with no known ladder just keeps its style at every depth. *)
$itemStyleHierarchy = <|"Item" -> {"Item", "Subitem", "Subsubitem"}|>;
nestedItemStyle[base_String, d_Integer] := With[
    {levels = Lookup[$itemStyleHierarchy, base, {base}]},
    levels[[Min[d + 1, Length[levels]]]]
]

(* The indent a nested bullet gets when its style family has no deeper style -
   the "Notes" bullets of a reference page's Details section being the case that
   matters: the doc stylesheet has no Sub-Notes style (no shipped ref page uses
   Subitem - 0 of the 6883 in the system documentation), so a sub-bullet keeps
   the Notes style and is nested by a left margin, the same CellMargins idiom
   the shipped pages use to indent content under a note. Without this a nested
   markdown list under "## Details" flattened to a single level. *)
nestedItemMargins[d_Integer] := CellMargins -> {{18 d + Inherited, Inherited}, {2 + Inherited, Inherited}}

nestedItemCell[text_String, base_String, d_Integer] := With[{style = nestedItemStyle[base, d]},
    If[ d > 0 && style === base,
        Cell[TextData @ inlineTextData[text], style, nestedItemMargins[d]],
        Cell[TextData @ inlineTextData[text], style]
    ]
]

(* list items as cells of the given bullet style, numbered ("ItemNumbered") when
   the block is an ordered list. An unordered block carries a parallel "Depths"
   list (from listBlock); each item's depth selects its nested style. *)
listItemCells[block_, base_String] := If[TrueQ[block["Ordered"]],
    Map[Cell[TextData @ inlineTextData[#], "ItemNumbered"] &, block["Items"]],
    With[{depths = Lookup[block, "Depths", ConstantArray[0, Length[block["Items"]]]]},
        MapThread[nestedItemCell[#1, base, #2] &, {block["Items"], depths}]
    ]
]

detailsCells[sections_] := Catenate @ Map[
    block |-> applyBlockMeta[Switch[block["Type"],
        "Prose", {Cell[TextData @ inlineTextData[block["Text"]], "Notes"]},
        "List", listItemCells[block, "Notes"],
        "Table", {tableCell[block]},
        "Quote", {quoteCell[block["Text"]]},
        "MathBlock", {mathBlockCell[block["Text"]]},
        _, {}
    ], block],
    (* The Notes slot is filled from the "Details" section. Accept both headings
       authors use for it: "## Details & Options" (the doc-tools title) and
       "## Details" alone. sectionKey normalizes " & " to " and ", so
       "Details & Options" is stored under "details and options"; look both up
       by key and concatenate so a page titled just "## Details" is not
       silently dropped (issue #8). A standalone "## Options" is deliberately
       NOT included - in a Symbol page it is an example section (it is in
       $resourceExampleOrder), so pulling it here would duplicate it. *)
    Join @@ Lookup[sections, sectionKey /@ {"Details & Options", "Details"}, {}]
]

notesSlot[opts_, sections_] := With[{cells = detailsCells[sections]},
    If[cells === {}, slotDefault[opts], cells]
]

(* the landing-page hero image: a "## Hero Image" section's first executable cell
   is evaluated; the rendered output is the visible image and the generating code
   is kept beneath it in a Closed cell group (a closed group shows only its first
   cell, so the image shows and the code stays available but hidden). Replaces
   the template's "Image Placeholder".
   Standard Input/Output group with the open state {2}, which shows only cell 2
   (the Output image) and collapses the code Input - the idiom working paclet
   definition notebooks use for a hero, so the scrape sees the image and the code
   stays available but hidden. *)
heroSlot[opts_, sections_] := Block[{cells = sectionCells[sections, "hero image"], out, code},
    If[ cells === {}, Return[slotDefault[opts]] ];
    out = First[cells]["OutputBoxes"];
    code = First[cells]["Code"];
    (* Self-healing fallback (issue #24): if the example-evaluation pass did
       not surface an output for the hero cell (whatever the capture gap in
       the hosting environment), evaluate the code directly here so a
       scripted/headless build never silently degrades the landing page to
       the template placeholder. Only when evaluation was requested -
       evalExamples is the entry Block's dynamic binding, False on
       "Evaluate" -> False builds, where the placeholder IS the right
       result. *)
    If[ (MissingQ[out] || out === Null) && TrueQ[evalExamples] && StringQ[code] && StringTrim[code] =!= "",
        out = Replace[
            Quiet @ Check[ToExpression[code], $Failed],
            {$Failed | _Missing | Null -> Missing[], r_ :> outputBoxes[r, First[cells]["Options"]]}
        ]
    ];
    If[ MissingQ[out] || out === Null, Return[slotDefault[opts]] ];
    (* NOTE: the hero image reaches the notebook but NOT the deployed landing
       page - ScrapeResource returns a Paclet resource with no "HeroImage" key,
       so the shingle renders an empty hero frame (the same is true of the
       other paclet examples, e.g. AccessibleColors, whose built definition
       notebook has the identical shape - this is not a regression). Neither
       emitting the code as Input plus the image as Output (below) nor a single
       Input cell holding the image, which is the shape of the template's own
       placeholder, makes the scrape pick it up; CheckDefinitionNotebook
       reports no hero hint either way. Left as the Input/Output pair, which
       keeps the generating code visible in the notebook. *)
    {Cell[CellGroupData[{
        Cell[BoxData[inputBoxes[code]], "Input"],
        Cell[BoxData[out], "Output"]
    }, {2}]]}
]

(* The FunctionResource template's VerificationTests slot accepts both Input /
   Output cell pairs and symbolic VerificationTest expressions. We always emit
   the explicit VerificationTest form: each wl code block in a "## Tests"
   section is expected to be a `VerificationTest[code, expected, TestID -> "..."]`
   expression (the docked Run Tests button evaluates these directly), so the
   slot just wraps each code block as a single Input cell tagged
   DefaultContent. Authors write the assertion explicitly - what is tested
   and what is expected - rather than relying on an Input/Output pair the
   scraper would otherwise infer the assertion from. *)
testsSlot[opts_, sections_] := Block[
    {cells = Cases[Lookup[sections, "tests", {}], b_ /; codeBlockQ[b]]},
    If[ cells === {}, Return[slotDefault[opts]] ];
    Map[
        Cell[BoxData[inputBoxes[#["Code"]]], "Input", CellTags -> {"DefaultContent"}] &,
        cells
    ]
]

(* the standard example sections a Function / Paclet resource carries, in
   canonical order. examplesSlot / exampleNotebookSlot emit all of them so a
   resource page has the full set in order, each section heading-only (a Closed
   Subsection) when the markdown does not fill it - matching the Symbol page's
   kept-empty More-Examples scaffold. *)
$resourceExampleOrder = {"basic examples", "scope", "generalizations and extensions",
    "options", "applications", "properties and relations", "possible issues", "neat examples"}

(* one example section as a Subsection group: heading + content, or a Closed
   heading-only group when the section is absent from the markdown. *)
exampleSubsectionGroup[sections_, key_] := With[{
        content = exampleContent[Lookup[sections, key, {}], "Text"],
        title = Cell[Lookup[$exampleTitle, key, Capitalize[key]], "Subsection"]},
    If[ content === {},
        Cell[CellGroupData[{title}, Closed]],
        Cell[CellGroupData[Prepend[content, title], Open]]
    ]
]

examplesSlot[opts_, sections_] := Block[{body},
    (* a document may put everything under a single "## Examples" section (the
       natural shape for an Example Repository resource, whose template has one
       Examples slot rather than the Function template's named example sections);
       fill the slot with that section's content directly, no subsection wrapper. *)
    If[ KeyExistsQ[sections, "examples"],
        body = exampleContent[Lookup[sections, "examples", {}], "Text"];
        If[body =!= {}, Return[body]]
    ];
    exampleSubsectionGroup[sections, #] & /@ $resourceExampleOrder
]

(* the cell that heads each example past the first within a section. The
   canonical DocumentationTools form (FunctionExample.nb) is an ExampleDelimiter
   cell whose BoxData is an InterpretationBox wrapping a "\t" delimiter cell with
   the held interpretation `$Line = 0; Null` - evaluating the delimiter resets
   the In[]/Out[] line counter so the next example starts at In[1]. (A bare
   `Cell["\t", "ExampleDelimiter"]` string cell mis-groups in the doc build, and
   an empty `Cell[BoxData[""], ...]` drops the line-reset.) It is the HEAD of the
   following example's CellGroupData (see exampleContent).
   InterpretationBox is HoldAllComplete, so the `$Line = 0` side effect is held,
   not run, while the converter assembles the cell. *)
exampleDelimiterCell := Cell[BoxData[InterpretationBox[Cell["\t", "ExampleDelimiter"], $Line = 0; Null]], "ExampleDelimiter"]

(* shared example-content builder: prose -> a text cell of the given style,
   tables -> a GridBox, executable cells -> evaluated Input/Output. Examples are
   separated explicitly by a thematic-break line (--- or ___), which becomes an
   ExampleDelimiter and restarts the In[]/Out[] counter - never inserted
   automatically. A "### Heading" becomes a subsubsection (an ExampleSubsection on
   doc pages) and likewise restarts the counter. *)
(* level-aware: a `####` heading inside an example section should become an
   ExampleSubsubsection, not flatten to the `###` ExampleSubsection style
   (issue #10). *)
exampleSubStyle["ExampleText", 4] = "ExampleSubsubsection"
exampleSubStyle["ExampleText", _] = "ExampleSubsection"
exampleSubStyle[_, _] = "Subsubsection"

(* Build the section as nested example groups, the shape DocumentationBuild
   expects (matching a hand-authored ref page): the first example's cells sit
   directly under the section; every later example - introduced by a `---`
   thematic break or a `### heading` - becomes its own CellGroupData HEADED by
   the ExampleDelimiter (or the ExampleSubsection heading) cell, holding that
   example's caption + Input/Output group. Emitting these flat instead made
   DocumentationBuild re-group by section and scatter the trailing examples onto
   the next section (basic examples drifting to Related Guides). `flush` closes
   the current chunk: the first (head None) goes in directly, the rest are
   wrapped under their boundary cell. *)
exampleContent[sectionBlocks_, textStyle_String] := Block[{counter = 0, chunks = {}, cur = {}, head = None, flush},
    flush[] := (
        AppendTo[chunks, If[head === None, cur, {Cell[CellGroupData[Prepend[cur, head], Open]]}]];
        cur = {}
    );
    Do[
        Which[
            block["Type"] === "Heading",
                flush[]; head = Cell[TextData @ inlineTextData[block["Text"]], exampleSubStyle[textStyle, block["Level"]]]; counter = 0,
            block["Type"] === "Separator",
                flush[]; head = exampleDelimiterCell; counter = 0,
            (* every content cell honors the block's #| directives (style / tags /
               annotation) via applyBlockMeta, exactly as defaultNotebook and
               proseBlockCells do - so "#| annotation:" before an example sentence
               or cell becomes a real annotation in the structured templates too. *)
            block["Type"] === "Prose",
                cur = Join[cur, applyBlockMeta[{Cell[TextData @ inlineTextData[block["Text"]], textStyle]}, block]],
            block["Type"] === "Table",
                cur = Join[cur, applyBlockMeta[{tableCell[block]}, block]],
            block["Type"] === "List",
                cur = Join[cur, applyBlockMeta[listItemCells[block, "Item"], block]],
            block["Type"] === "Quote",
                cur = Join[cur, applyBlockMeta[{quoteCell[block["Text"]]}, block]],
            block["Type"] === "MathBlock",
                cur = Join[cur, applyBlockMeta[{mathBlockCell[block["Text"]]}, block]],
            block["Type"] === "Image",
                cur = Join[cur, applyBlockMeta[{imageCell[block]}, block]],
            executableQ[block],
                counter += 1; cur = Join[cur, applyBlockMeta[exampleIOFor[block, counter], block]],
            block["Type"] === "Code",
                cur = Join[cur, applyBlockMeta[withCellFlag[block, {nonExecutableCell[block]}], block]]
        ],
        {block, sectionBlocks}
    ];
    flush[];
    Catenate[chunks]
]

(* Paclet "ExampleNotebook" slot: unlike the Function template's "Examples" slot,
   the example sub-sections are literal Subsection/Text/Input/Output cells (not a
   slot). Keep the template's ExampleInitialization group (the PacletDirectoryLoad
   + Needs cells, filled from PacletDirectory/Context), then build one Subsection
   group per example section with the markdown's prose and evaluated I/O. *)
exampleNotebookSlot[opts_, sections_] := Block[{def = slotDefault[opts], initGroup, keys, groups},
    initGroup = FirstCase[def,
        g : Cell[CellGroupData[{Cell[_, "Subsection", "Excluded", ___], _TemplateSlot, ___}, _], ___] :> g,
        Nothing, Infinity];
    (* emit only the example sections the author actually wrote (in canonical order) - a Paclet
       home page should not ship the eight empty Basic Examples..Neat Examples placeholder
       subsections the generic Function template scaffolds. The ExampleInitialization group
       (PacletDirectoryLoad + Needs) is kept as the first surviving section's lead-in, or on its
       own when no example section has content. *)
    keys = Select[$resourceExampleOrder, exampleContent[Lookup[sections, #, {}], "Text"] =!= {} &];
    groups = exampleSubsectionGroup[sections, #] & /@ keys;
    Which[
        groups =!= {},
            Prepend[Rest[groups],
                Replace[First[groups], Cell[CellGroupData[cells_, st_], o___] :>
                    Cell[CellGroupData[Join[Flatten[{initGroup}], cells], st], o]]],
        initGroup === Nothing, {},
        True, Flatten[{initGroup}]
    ]
]

(* === slot dispatch === *)

fillSlot[name_, opts_, data_] := Block[{meta = data["meta"]},
    Switch[name,
        "Name", fillTextCells[opts, Lookup[meta, "Name", ""]],
        "Description", fillTextCells[opts, Lookup[meta, "Description", ""]],
        "Contributed By", fillTextCells[opts, Lookup[meta, "ContributedBy", ""]],
        "ContributorInformation", fillTextCells[opts, Lookup[meta, "ContributedBy", ""]],
        "ContentElements", contentSlot[opts, data["sections"]],
        "Keywords", fillListCells[opts, asList @ Lookup[meta, "Keywords", {}]],
        "Links", fillLinkCells[opts, asList @ Lookup[meta, "Links", {}]],
        "SourceControlURL", fillTextCells[opts, Lookup[meta, "SourceControlURL", ""]],
        "Source/Reference Citation", fillListCells[opts, asList @ Lookup[meta, "Sources", {}]],
        "Related Symbols", fillListCells[opts, asList @ Lookup[meta, "RelatedSymbols", Lookup[meta, "SeeAlso", {}]]],
        "RelatedSymbols", fillListCells[opts, asList @ Lookup[meta, "RelatedSymbols", Lookup[meta, "SeeAlso", {}]]],
        "Related Resource Objects", fillListCells[opts, asList @ Lookup[meta, "RelatedResources", {}]],
        "Categories",
            If[ KeyExistsQ[meta, "Categories"],
                fillCheckbox["Categories", asList @ meta["Categories"], Lookup[data, "resourceType", "Function"]],
                slotDefault[opts]
            ],
        "CompatibilityOperatingSystem",
            If[ KeyExistsQ[meta, "OperatingSystems"],
                fillCheckbox["CompatibilityOperatingSystem",
                    Lookup[$osCanonical, ToLowerCase /@ asList[meta["OperatingSystems"]], Nothing]],
                slotDefault[opts]
            ],
        "CompatibilityEvaluationEnvironment",
            If[ KeyExistsQ[meta, "Environments"],
                fillCheckbox["CompatibilityEvaluationEnvironment", asList @ meta["Environments"]],
                slotDefault[opts]
            ],
        "CompatibilityCloudSupport",
            If[ KeyExistsQ[meta, "CloudSupport"],
                fillCheckbox["CompatibilityCloudSupport", If[TrueQ @ meta["CloudSupport"], {True}, {}]],
                slotDefault[opts]
            ],
        "Function", functionSlot[opts, data["defCode"], data["sections"]],
        "HeroImage", heroSlot[opts, data["sections"]],
        "Usage", usageSlot[opts, data["sections"]],
        "Notes", notesSlot[opts, data["sections"]],
        "Details", notesSlot[opts, data["sections"]],
        (* the main description prose: a resource keys it under "## Usage", a Paclet page
           under "## Basic Description" - fall back so the Paclet LongDescription fills too *)
        "LongDescription", fillTextDataCells[opts,
            Replace[rawSectionText[data["sections"], "usage"], "" :> rawSectionText[data["sections"], "basic description"]]],
        "PrimaryContext", fillTextCells[opts, Lookup[meta, "Context", ""]],
        "Examples", examplesSlot[opts, data["sections"]],
        "ExampleNotebook", exampleNotebookSlot[opts, data["sections"]],
        "VerificationTests", testsSlot[opts, data["sections"]],
        (* fillTextDataCells routes the text through inlineTextData so a
           markdown link, italic, backtick code span, or inline math in the
           Author Notes section actually renders. The previous bare-string
           splice left "[label](url)" as literal text in the cell. *)
        "Author Notes", fillTextDataCells[opts, sectionText[data["sections"], "author notes"]],
        "CompatibilityFeatures",
            If[ KeyExistsQ[meta, "Features"],
                fillCheckbox["CompatibilityFeatures", asList @ meta["Features"]],
                slotDefault[opts]
            ],
        "CompatibilityWolframLanguageVersionRequired",
            fillTextCells[opts, Lookup[meta, "WolframVersion", "14.0+"]],
        (* Data Repository: statistical-metadata fields. Each is a Text cell; accept
           either the SMD-prefixed key or the cleaner alias (Author / Title / ...). *)
        "SMDAuthor", fillTextCells[opts, Lookup[meta, "Author", Lookup[meta, "SMDAuthor", Lookup[meta, "ContributedBy", ""]]]],
        "SMDTitle", fillTextCells[opts, Lookup[meta, "Title", Lookup[meta, "SMDTitle", Lookup[meta, "Name", ""]]]],
        "SMDDate", fillTextCells[opts, Lookup[meta, "Date", Lookup[meta, "SMDDate", ""]]],
        "SMDPublisher", fillTextCells[opts, Lookup[meta, "Publisher", Lookup[meta, "SMDPublisher", ""]]],
        "SMDGeographicCoverage", fillTextCells[opts, Lookup[meta, "GeographicCoverage", Lookup[meta, "SMDGeographicCoverage", ""]]],
        "SMDTemporalCoverage", fillTextCells[opts, Lookup[meta, "TemporalCoverage", Lookup[meta, "SMDTemporalCoverage", ""]]],
        "SMDLanguage", fillTextCells[opts, Lookup[meta, "Language", Lookup[meta, "SMDLanguage", ""]]],
        "SMDRights", fillTextCells[opts, Lookup[meta, "Rights", Lookup[meta, "SMDRights", ""]]],
        "Citation",
            fillTextCells[opts, Lookup[meta, "Citation", sectionText[data["sections"], "citation"]]],
        "ContentTypes",
            If[ KeyExistsQ[meta, "ContentTypes"],
                fillCheckbox["ContentTypes", asList @ meta["ContentTypes"], Lookup[data, "resourceType", "Data"]],
                slotDefault[opts]
            ],
        "SubmissionNotes",
            With[{sn = Lookup[meta, "SubmissionNotes", ""]},
                If[sn === "", slotDefault[opts], fillTextCells[opts, sn]]
            ],
        (* === Prompt Repository slots ===
           PromptTemplate is the prompt body (a "## Prompt" section of plain prose).
           The optional WL slots (PersonaIcon, CellProcessingFunction, ...) pull
           the first code block of the matching section into the template's input
           cell. SampleChat / Examples / Notes / Usage reuse the existing helpers. *)
        "PromptTemplate", proseSectionSlot[opts, data["sections"], "prompt", "Text"],
        "PersonaIcon", codeSlot[opts, data["sections"], "persona icon"],
        "CellProcessingFunction", codeSlot[opts, data["sections"], "cell processing function"],
        "CellPostEvaluationFunction", codeSlot[opts, data["sections"], "cell post evaluation function"],
        "PromptInterpreter", codeSlot[opts, data["sections"], "output interpreter"],
        "Tools", codeSlot[opts, data["sections"], "llm tools"],
        "LLMConfigurationExtra", codeSlot[opts, data["sections"], "llm configuration"],
        "SampleChat", multiCodeSlot[opts, data["sections"], "chat examples"],
        "Topics", fillListCells[opts, asList @ Lookup[meta, "Topics", {}]],
        (* === LLMTool slots ===
           A Tool resource exposes a callable LLMTool with a name +
           one-sentence ToolDescription (used by the model to decide whether to
           call it), a parameter spec, and the actual function body. Three of
           the slots take one code block each from the matching named section. *)
        "ToolDescription", fillTextDataCells[opts, sectionText[data["sections"], "tool description"]],
        "ToolParameters", codeSlot[opts, data["sections"], "tool parameters"],
        "ToolFunction", codeSlot[opts, data["sections"], "tool function"],
        "ToolAppearanceRules", codeSlot[opts, data["sections"], "tool appearance"],
        (* === Demonstration slots ===
           A Demonstration's content is split across named sections rather than the
           Function template's TemplateSlots: Caption / Initialization / Manipulate /
           Snapshots / Details / References each map to one slot. AuthorNames takes
           a frontmatter list (one cell per author item, falling back to ContributedBy
           for the common single-author case). RelatedDemonstrations is the
           "see also" of other Demos. *)
        "CaptionCells", proseSectionSlot[opts, data["sections"], "caption", "Text"],
        "InitializationCode", codeSlot[opts, data["sections"], "initialization"],
        "ManipulateGroup", manipulateSlot[opts, data["sections"]],
        "SnapshotGroup", multiCodeSlot[opts, data["sections"], "snapshots"],
        "AuthorNames",
            With[{vs = asList @ Lookup[meta, "AuthorNames", Lookup[meta, "ContributedBy", ""]]},
                fillListCells[opts, DeleteCases[vs, ""]]
            ],
        "DetailCells", proseSectionSlot[opts, data["sections"], "details", "Text"],
        "ReferenceCells", proseSectionSlot[opts, data["sections"], "references", "Text"],
        "RelatedDemonstrations", fillListCells[opts, asList @ Lookup[meta, "RelatedDemonstrations", {}]],
        "ExternalLinks", fillLinkCells[opts, asList @ Lookup[meta, "Links", {}]],
        "CompatibilityARSupport",
            If[ KeyExistsQ[meta, "ARSupport"],
                fillCheckbox["CompatibilityARSupport", If[TrueQ @ meta["ARSupport"], {True}, {}]],
                slotDefault[opts]
            ],
        _, slotDefault[opts]
    ]
]

(* === documentation-page builders (Symbol / Guide) ===
   These templates are styled placeholders (no TemplateSlot): we start from the
   authoring template (which carries the page stylesheet + docked Build toolbar)
   and replace placeholder cells, then seed the build metadata. DocsBuild later
   adds the AnchorBar / FooterCell. *)

$docResourceDir := FileNameJoin[{$InstallationDirectory, "AddOns", "Applications", "DocumentationTools", "FrontEnd", "TextResources"}]

docTemplate[file_String] := Get[FileNameJoin[{$docResourceDir, file}]]

(* Doc-page placeholder cells (ObjectName / GuideTitle / GuideAbstract / Title)
   hold prose that can carry the same inline markup other prose does -
   backticks, bold / italic / strike, math, links. headingText runs the value
   through inlineTextData and wraps the result as TextData (or keeps the bare
   string when nothing matched), so a "## Abstract" paragraph with
   "[Accessibility](paclet:guide/Accessibility)" or "`ColorConvert`" renders
   the link / code span instead of dumping the literal markdown into the cell. *)
fillDocString[nb_, style_String, value_String] := If[ value === "",
    nb,
    nb /. Cell["XXXX", style, o___] :> Cell[headingText[value], style, o]
]

(* replace the placeholder cells of a style with one cell per item (first match
   expands to all items; any further placeholders of that style are dropped) *)
fillDocList[nb_, style_String, items_List] := Block[{vals = DeleteCases[items, ""], first = True},
    If[ vals === {},
        nb,
        nb /. Cell["XXXX", style, o___] :> If[ first,
            first = False; Sequence @@ Map[Cell[#, style, o] &, vals],
            Sequence @@ {}
        ]
    ]
]

(* the paclet-name URI segment the DocumentationTools link templates use:
   paclet:Publisher/Name/ref/Sym - slash preserved (issue #23). The local
   doc-center resolver keys on the paclet Name verbatim (when no LinkBase
   is set), so a flattened "PublisherName" form matches nothing and inferred
   links are dead in-notebook (CloudPublish's web rewrite drops the segment
   either way, which is why the older flattening looked fine on the deployed
   page). Falls back to the Context with backtick segments rewritten as
   slashes when no Paclet frontmatter is set. *)
packagePath[paclet_String, context_String] := Which[
    paclet =!= "", paclet,
    context =!= "", StringReplace[StringTrim[context, "`"], "`" -> "/"],
    True, ""
]
packagePath[paclet_String] := packagePath[paclet, $docContext]

(* the DocumentationTools-shaped typed link boxes (issue #20).  PackageLink for a
   paclet symbol (3-arg, "<Flat> Package Symbol" tag), RefLink for a System
   symbol, RefLinkPlain for a guide / tutorial / other paclet-scheme target.
   The doc center's link resolver and CloudPublish's paclet: -> web rewrite key
   off these templates, so plain ButtonBox links get silently dropped. *)
packageLinkBox[name_, url_String, pkg_String] := TemplateBox[
    {Cell[TextData[name]], url, pkg <> " Package Symbol"},
    "PackageLink", BaseStyle -> "InlineFormula"
]
refLinkBox[name_, url_String] := TemplateBox[
    {Cell[TextData[name]], url}, "RefLink", BaseStyle -> "InlineFormula"
]
refLinkPlainBox[label_, url_String, baseSty_:Automatic] := TemplateBox[
    {Cell[TextData[label]], url},
    "RefLinkPlain",
    BaseStyle -> Replace[baseSty, Automatic -> {"InlineFormula"}]
]

(* dispatch a "paclet:..." link target to the corresponding typed TemplateBox
   (issue #20).  Mirrors DocumentationBuild's ConvertButtonBox:
   paclet:<Pkg>/ref/<Sym> -> PackageLink (Pkg is the paclet Name with the
   slash preserved, e.g. Publisher/Name - see #23, packagePath);
   paclet:ref/<Sym> -> RefLink; anything else under paclet: -> RefLinkPlain.
   The URL is passed through verbatim - never reassembled with StringJoin -
   so a Publisher/Name paclet keeps its slash in the linkbase segment. *)
pacletLinkBox[label_, url_String] := Block[{rest, parts, pkg},
    rest = StringDelete[url, StartOfString ~~ "paclet:"];
    parts = StringSplit[rest, "/"];
    Which[
        Length[parts] >= 3 && parts[[-2]] === "ref",
            pkg = StringRiffle[parts[[;; -3]], "/"];
            packageLinkBox[label, url, pkg],
        Length[parts] === 2 && parts[[1]] === "ref",
            refLinkBox[label, url],
        Length[parts] >= 3 && MemberQ[{"guide", "tutorial"}, parts[[-2]]],
            refLinkPlainBox[label, url],
        True, refLinkPlainBox[label, url]
    ]
]

(* a resolved documentation link, e.g. paclet:WolframAccessibleColors/ref/WCAGLevel.
   Wraps the typed-link TemplateBox in an InlineFormula cell (issue #20). *)
docLinkCell[name_String, uri_String] :=
    Cell[BoxData[pacletLinkBox[name, "paclet:" <> uri]], "InlineFormula"]

(* the link target for a See Also / More About entry.  A System symbol (e.g.
   StandardRed, LightDarkSwitched) points at its system ref page; a guide is
   paclet-qualified for the documented paclet (the typed-link templates need
   the qualified path; a bare paclet:guide/Name is the System form).  The URI
   carries the paclet name verbatim, slash preserved (issue #23). *)
linkURI[name_String, paclet_String, kind_String] := Block[{pkg = packagePath[paclet, $docContext]},
    Which[
        kind === "ref" && symbolInContextQ[name, "System`"] && ! symbolInDocQ[name],
            "ref/" <> name,
        kind === "guide" && symbolInContextQ[name, "System`"] && ! symbolInDocQ[name] && pkg === "",
            "guide/" <> name,
        pkg =!= "",
            pkg <> "/" <> kind <> "/" <> name,
        True,
            kind <> "/" <> name
    ]
]

(* a related-guide / related-tutorial link cell: a RefLinkPlain TemplateBox
   wrapped in an InlineFormula BoxData cell inside TextData (issue #20).  The
   BoxData wrapper is required: a bare TemplateBox directly in TextData breaks
   Export[..., "NB"] (the SeeAlso path does the same via docLinkCell). *)
guideLinkContent[name_String, paclet_String, kind_String] :=
    TextData[Cell[BoxData[refLinkPlainBox[name, "paclet:" <> linkURI[name, paclet, kind]]], "InlineFormula"]]

(* fill a style's XXXX placeholders with one cell per given content expression *)
fillDocCells[nb_, style_String, contents_List] := Block[{vals = contents, first = True},
    If[ vals === {},
        nb,
        nb /. Cell["XXXX", style, o___] :> If[ first,
            first = False; Sequence @@ Map[Cell[#, style, o] &, vals],
            Sequence @@ {}
        ]
    ]
]

(* DocumentationBuild's symbol-page Related Guides harvester requires a plain
   Link ButtonBox in each MoreAbout cell (its Make step does
   First @ Cases[cell, _ButtonBox, Infinity, 1] and dies on First[{}] when the
   cell holds a typed TemplateBox instead); the build retypes the link itself
   in the built page, so the authoring notebook carries the palette's
   ButtonBox form there.  The other link-row styles (SeeAlso,
   TutorialMoreAbout, RelatedTutorials) pass typed boxes through fine. *)
guideButtonCell[name_String, paclet_String, kind_String] := Cell[BoxData[
    ButtonBox[name, BaseStyle -> "Link", ButtonData -> "paclet:" <> linkURI[name, paclet, kind]]
], "InlineFormula"]

(* a See Also / Related Symbols entry written as ResourceFunction["Name"] is a
   Wolfram Function Repository function, not a paclet symbol: it has no paclet
   ref page, so a paclet:.../ref/ResourceFunction[...] target is dead. Detect it
   and link the resource name to its repository page instead. Returns the
   resource name, or None when the entry is an ordinary symbol. *)
resourceFnName[entry_String] := Replace[
    StringCases[StringTrim[entry],
        StartOfString ~~ "ResourceFunction[" ~~ ("\"" | "'") ~~
            n : Shortest[Except["\"" | "'"] ..] ~~ ("\"" | "'") ~~ "]" ~~ EndOfString :> n, 1],
    {{n_} :> n, _ -> None}
]

resourceFnURL[name_String] :=
    "https://resources.wolframcloud.com/FunctionRepository/resources/" <> name <> "/"

(* the resource name as a code-styled hyperlink to its Function Repository page,
   shaped like the other See Also entries (InlineFormula BoxData cell).

   ButtonData is the bare URL *string*, NOT the usual {URL[url], None} pair:
   DocumentationBuild harvests every See Also ButtonData (GetSeeAlsoSectionList)
   and feeds it to ToPacletURI for the anchor-bar nav, and ToPacletURI errors on
   a non-string ({URL[...], None}) - it just prepends "paclet:" to a string. The
   "Hyperlink" style's ButtonFunction is NotebookLocate[#2], which opens a URL
   string in the browser, so a string target still clicks through to the web. *)
resourceFnLinkCell[name_String] := With[{url = resourceFnURL[name]},
    Cell[BoxData[
        ButtonBox[name, BaseStyle -> "Hyperlink", ButtonData -> url, ButtonNote -> url]
    ], "InlineFormula"]
]

linkRowCell[names_List, style_String, paclet_String, kind_String] := Cell[
    TextData @ Riffle[
        Map[
            With[{rf = resourceFnName[#]}, Which[
                rf =!= None,           resourceFnLinkCell[rf],
                style === "MoreAbout", guideButtonCell[#, paclet, kind],
                True,                  docLinkCell[#, linkURI[#, paclet, kind]]
            ]] &,
            names
        ],
        " \[FilledVerySmallSquare] "
    ],
    style
]

(* === usage line rendering (matches reference-page formatting) === *)

(* prose of a section without stripping inline-code backticks *)
rawSectionText[sections_, key_] := StringRiffle[
    Cases[Lookup[sections, key, {}], b_ /; b["Type"] === "Prose" :> b["Text"]],
    " "
]

(* The DocumentationTools "Template Input" button parses the selected text into
   InlineFormula boxes (arguments italic, c$1 subscripts, ...) and lets
   DocumentationBuild linkify the known symbols at build time. The button itself
   (DocumentationTools`FunctionTemplate) is coupled to the front-end selection;
   the transformation under it is DocumentationTools`Private`ParseTextTemplate,
   which takes a plain string and the documented object's name. We call that
   directly for every `code` span, so the boxes match the button exactly. *)

(* the documented symbol's name, its paclet, and its context, set per build. The
   name is passed to ParseTextTemplate (to resolve sym::tag); the paclet+context
   pair turns symbol-name tokens into reference links. *)
$docName = ""
$docPaclet = ""
$docContext = ""
$docTemplate = ""

(* the contexts a page loads before its example code runs: the primary "Context"
   followed by any extra "ContextPath" entries (a frontmatter list), deduped and
   stripped of empties / System`. Single source of truth for both the build-time
   evaluation $ContextPath (preloadContextPath Needs each) and the runtime
   ExampleInitialization cell (the reader's load). "Context" stays the single
   PRIMARY context ($docContext, PrimaryContext, Categorization); "ContextPath"
   carries the rest, so a page whose examples span several packages loads them
   all. *)
docContextList[meta_] := DeleteDuplicates @ DeleteCases[
    Flatten @ {Lookup[meta, "Context", Nothing], Lookup[meta, "ContextPath", {}]},
    "" | "System`"]

(* the ExampleInitialization cell body: one Needs[] per documented context *)
exampleInitCode[meta_] := StringRiffle[
    ("Needs[\"" <> # <> "\"]") & /@ docContextList[meta], "\n"]

(* the font LaTeX math (LaTeXMathParse output) is restyled to. Holds the resolved
   "MathFont" option value (see applyMathFont):
     None / "" / Automatic - keep the FE-native math font (the default): deterministic
                  across machines and correctly sized inline;
     "Family"   - rewrite every math expression to that Computer-Modern-like family
                  (Latin Modern Math, CMU Serif, ...) for the LaTeX / MaTeX look.
   Set per build from the "MathFont" option. *)
$mathFontFamily = None

(* Subscripts in a usage signature use the portable HTML form "x<sub>i</sub>" (works
   in every markdown renderer and on GitHub), with "x~i~" accepted as the Pandoc
   shorthand. Both forms are rewritten to ParseTextTemplate's "x$i" template form
   so its existing subscript handling does the rest. *)
mdToTemplateSubs[s_String] := StringReplace[s, {
    "<sub>" ~~ i:Shortest[Except["<"]..] ~~ "</sub>" :> "$" <> i,
    "~" ~~ i:Shortest[Except["~"]..] ~~ "~" :> "$" <> i
}]

templateBox[code_String] := Block[{boxes, prepped = mdToTemplateSubs[StringTrim[code]]},
    (* a path / URL / dotted filename is not a signature - keep it verbatim
       instead of letting ParseTextTemplate tokenise its / . ~ as operators
       (same guard as inputBoxes; see verbatimInlineQ). *)
    If[verbatimInlineQ[prepped], Return[prepped]];
    Needs["DocumentationTools`"];
    boxes = Quiet @ UsingFrontEnd @ DocumentationTools`Private`ParseTextTemplate[prepped, $docName];
    (* fall back to a plain parse if the front-end template parse is unavailable *)
    If[ FreeQ[boxes, $Failed] && (StringQ[boxes] || MatchQ[Head[boxes], RowBox | StyleBox | SubscriptBox | SuperscriptBox | FractionBox | SqrtBox]),
        boxes,
        inputBoxes[prepped]
    ]
]

(* A "<code>...</code>" span: strip the markdown link / italic wrappers in the
   inner signature, run it through the same templateBox pipeline a Usage
   signature uses (italic args via ParseTextTemplate), and wrap the result in
   a single InlineFormula cell so the code styling covers the whole span -
   brackets included - and not just the linked head. The leading head is
   wrapped in a paclet-link ButtonBox via inferURL when the name resolves
   (in $docContext or System`); ParseTextTemplate by itself does not link a
   page's own symbol, but a "<code>[Self]()</code>" reference should still
   render as a tappable link to the symbol's own ref page. *)
(* unescape markdown's backslash-punctuation in a prose-bearing context (link
   labels, <code>...</code> bodies). Wolfram named-character escapes
   ("\[Theta]", "\[CircleTimes]", ...) share the leading "\[" with markdown's
   "\[" escape for a literal "[", so the Wolfram-name rule runs FIRST: at a
   "\[CircleTimes]" position it matches and rebuilds the escape verbatim,
   blocking the punctuation rule from eating the "\" and turning the kernel
   char into a stray "[CircleTimes]". *)
unescapeMarkdownPunctuation[s_String] := StringReplace[s, {
    "\\[" ~~ name : (LetterCharacter ..) ~~ "]" :> "\\[" <> name <> "]",
    "\\" ~~ c : PunctuationCharacter :> c
}]

codeInlineCell[inner_String] := Block[{sig, head, url, boxes, unescaped},
    (* "<code>...</code>" content lets markdown formatting through (links,
       italics, math), so backslash-punctuation escapes inside it are markdown
       source escapes and unescape before any further processing - same rule
       inlineTextData applies to prose. Without this, an authored "\*" inside
       <code> would land in the .nb as literal "\*" instead of "*", which a
       markdown viewer renders as just "*" but the notebook would show the
       backslash. Backticked spans skip this because backticks freeze content
       by design - "\*" in `` `code` `` is meant to be literal. *)
    unescaped = decodeEntities @ unescapeMarkdownPunctuation[inner];
    sig = mathArgsToTemplate @ unwrapMarkdownSig @ unescaped;
    head = First[StringCases[sig,
        StartOfString ~~ h : ((LetterCharacter | "$") ~~ (WordCharacter | "$" | "`") ...) :> h, 1], ""];
    url = If[head =!= "", inferURL[head], None];
    boxes = templateBox[sig];
    If[ url =!= None,
        (* wrap the head token in the typed paclet link (issue #20) so the doc
           center / CloudPublish resolve it the same way DocumentationBuild does. *)
        boxes = Replace[boxes, {
            s_String /; s === head :> pacletLinkBox[s, url],
            RowBox[{s_String /; s === head, rest___}] :>
                RowBox[{pacletLinkBox[s, url], rest}]
        }]
    ];
    Cell[BoxData @ boxes, "InlineFormula", FontSize -> $inlineFontSize]
]

(* A paclet's public symbols may live in subcontexts of its primary context
   (an umbrella context whose loader only pushes the subpackages onto
   $ContextPath), so a documented name also counts when a non-Private
   subcontext of ctx defines it - e.g.
   Wolfram`DiagrammaticComputation`Diagram`Diagram for
   ctx = Wolfram`DiagrammaticComputation` and name = Diagram. *)
symbolInContextQ[name_String, ctx_String] := ctx =!= "" &&
    StringMatchQ[name, (LetterCharacter | "$") ~~ (WordCharacter | "$") ...] &&
    Quiet[
        Names[ctx <> name] =!= {} ||
        AnyTrue[Names[ctx <> "*`" <> name], ! StringContainsQ[#, "`Private`"] &]
    ]

(* the paclet's primary context derived from its name, e.g.
   "Wolfram/DiagrammaticComputation" -> "Wolfram`DiagrammaticComputation`". *)
docPacletContext[] := If[$docPaclet === "", "", StringReplace[$docPaclet, "/" -> "`"] <> "`"]

(* whether a bare name is a documented symbol of THIS paclet: it counts when it
   resolves in the document's own Context or in the paclet's primary context (or a
   non-Private subcontext of either, via symbolInContextQ). A subpackage page whose
   Context is e.g. Wolfram`DiagrammaticComputation`Rewriting` therefore also links
   the paclet's main-context symbols - the doc-build mirror of the subpackage
   PackageImport-ing its parent paclet at load. *)
symbolInDocQ[name_String] := symbolInContextQ[name, $docContext] ||
    With[{primary = docPacletContext[]}, primary =!= $docContext && symbolInContextQ[name, primary]]

(* drop every ButtonBox link wrapper, keeping its content. ParseTextTemplate
   eagerly links any System symbol it recognizes (Notebook, ResourceFunction,
   ...), which renders as ugly inline links - especially a whole expression like
   ResourceFunction["..."]. We strip those so a usage signature reads as code. *)
stripLinks[boxes_] := boxes //. ButtonBox[content_, ___] :> content

(* prose inline `code` is just an InlineFormula cell - no auto-linking, even
   when the body is a known symbol name. Linking is opt-in via the explicit
   "[`Name`]()" / "[Name]()" form (handled by linkInferred) so that a name
   that collides with a WL symbol but means something else in context (a TeX
   environment named "Cases", an English word "Range", a variable "x") is
   not turned into a ref-page link the author did not ask for.

   A path / URL / filename must be a *string-content* InlineCode cell, NOT
   BoxData: the front end re-parses a bare string inside BoxData when it
   renders the notebook, tokenising the path's / . ~ back into WL operators
   (`config . json`) - even though the stored box was a plain string. A
   string-content Cell renders the characters verbatim and never reparses.
   (Real WL code is unaffected: inputBoxes returns proper boxes for it, not a
   bare string, so the FE has nothing to reparse.) *)
codeToInline[code_String] /; verbatimInlineQ[StringTrim[code]] :=
    Cell[StringTrim[code], "InlineCode"]
codeToInline[code_String] := Cell[BoxData[inputBoxes[code]], "InlineFormula", FontSize -> $inlineFontSize]

(* double-backtick ``code`` -> the palette's "Code (Inline)": a literal,
   non-linkified monospace span (InlineCode), unlike Template Input. *)
(* a double-backtick verbatim span. CommonMark keeps the spaces just inside the
   backticks (`` `x` `` -> " `x` "), but those padding spaces trip the notebook
   analysis "extra whitespace" check, so trim them. *)
literalCodeInline[code_String] := Cell[BoxData[StyleBox[StringTrim[code], "InlineCode"]], "InlineCode"]

(* inline emphasis -> styled text runs. Bold is FontWeight, strikethrough a
   FontVariation; italic keeps the "TI" (text-italic) style usage descriptions
   already mark arguments with. The styled content is a plain string (not re-parsed),
   so a single emphasis level is supported, which covers ordinary prose. *)
(* Wrap a single inlineTextData element (a string, StyleBox, InlineFormula
   Cell, ButtonBox, ...) with one more layer of styling, merging into any
   existing StyleBox / Cell options so a nested "**$x$**" produces an
   InlineFormula whose own option list carries the bold attribute rather
   than a hopeless StyleBox-of-Cell. Hyperlinks pass through unchanged -
   inheriting a parent bold would clobber the link's own styling. *)
wrapStyle[s_String, opts_List] := StyleBox[s, Sequence @@ opts]
wrapStyle[StyleBox[c_, existing___], opts_List] := StyleBox[c, existing, Sequence @@ opts]
wrapStyle[Cell[content_, style_String, cellOpts___], opts_List] :=
    Cell[content, style, cellOpts, Sequence @@ opts]
wrapStyle[ButtonBox[args___], _] := ButtonBox[args]
wrapStyle[other_, _] := other

(* Bold / italic / strike runs that may carry other inline markup ("**$x$**",
   "***`code`***", "~~bold $y$~~", ...) recursively re-enter inlineTextData
   on the inner text so any math / code / link spans are processed first;
   the formatting is then distributed across each resulting element via
   wrapStyle. Returning a Sequence keeps the surrounding StringSplit's
   result list flat. *)
(* the recursive emphasis call goes through inlineTextDataCore so the outer
   inlineTextData's link-box stash (Block-dynamic $inlineLinkBoxes) is
   visible - otherwise nested **[a](u)** would lose the pre-extracted link
   when the bold rule recurses. *)
emWith[s_String, opts_List] := Sequence @@ Map[wrapStyle[#, opts] &, inlineTextDataCore[s]]

emBoldBox[s_String] := emWith[s, {FontWeight -> "Bold"}]
emItalicBox[s_String] := emWith[s, {"TI"}]
emBoldItalicBox[s_String] := emWith[s, {"TI", FontWeight -> "Bold"}]
emStrikeBox[s_String] := emWith[s, {FontVariations -> {"StrikeThrough" -> True}}]

(* A heading's text can carry the same inline markup prose does - backticks,
   bold, italic, math, links. Run it through inlineTextData and wrap the
   result as TextData so a "## A `foo` heading" or "## Bold **$x$**" renders
   the code span / bold math correctly. If the result is a single plain
   string, keep it bare - the simple "## Plain heading" stays Cell["Plain
   heading", "Section"] and Symbol-page tooling expecting a string content
   keeps working. *)
headingText[text_String] := Block[{td = inlineTextData[text]},
    If[Length[td] == 1 && StringQ[td[[1]]], td[[1]], TextData[td]]
]

(* Pandoc / GFM markdown subscript "x~n~" and superscript "x^n^". The script is
   rendered as a one-character formula cell (SubscriptBox / SuperscriptBox with an
   empty base), which sits inline at the right baseline in TextData. *)
proseSubBox[s_String] := Cell[BoxData[SubscriptBox["", s]], "InlineFormula"]
proseSupBox[s_String] := Cell[BoxData[SuperscriptBox["", s]], "InlineFormula"]

(* underscore emphasis (_em_, __strong__), applied to a plain prose run *after* the
   main split has pulled out code / links / math. CommonMark only treats underscores
   as emphasis at word boundaries, so a snake_case identifier in prose is left alone;
   enforce that with lookarounds, then split on private-use sentinels (the regex
   replacement string cannot itself build boxes). *)
underscoreEm[s_String] := If[! StringContainsQ[s, "_"], {s},
    StringSplit[
        StringReplace[s, {
            RegularExpression["(?<![A-Za-z0-9_])__(\\S|\\S.*?\\S)__(?![A-Za-z0-9_])"] -> "\:f8f1$1\:f8f2",
            RegularExpression["(?<![A-Za-z0-9_])_(\\S|\\S.*?\\S)_(?![A-Za-z0-9_])"] -> "\:f8f3$1\:f8f4"
        }],
        {
            "\:f8f1" ~~ c : Shortest[__] ~~ "\:f8f2" :> emBoldBox[c],
            "\:f8f3" ~~ c : Shortest[__] ~~ "\:f8f4" :> emItalicBox[c]
        }
    ]
]

(* an inline image ![alt](src): embed the imported graphic, or, when it cannot be
   loaded (e.g. a path relative to a base this context does not have), fall back to a
   plain link so the text is never left with a stray "!" the way an unhandled image
   span would be. *)
inlineImage[alt_String, src_String] := Block[{img = Quiet @ Import[src]},
    If[ MatchQ[img, _Image | _Graphics | _Legended | _Graphics3D],
        Cell[BoxData @ ToBoxes[img], "InlineFormula"],
        textDataLinkBox @ linkButton[If[StringTrim[alt] === "", src, alt], src]
    ]
]

(* $math$ -> inline math; $$math$$ -> centered display math. The content is TeX
   (LaTeX math notation). The Wolfram`Parser`LaTeX` paclet (when installed)
   is preferred - its LaTeXMathParse handles \mathbb / \frac / big operators
   / Greek / named symbols properly. Fall back to ImportString[..., "TeX"]
   (the built-in importer that drops styling) when the paclet isn't
   available, and to a Wolfram-expression parse if that also fails. *)

(* Restyle LaTeXMathParse output to $mathFontFamily by delegating to the parser
   paclet's LaTeXMathStyle - it remaps italic letters to their math-italic
   codepoints for an OpenType math font, pulls \mathbb into MSBM10, and wraps in
   the family.  Resolved at runtime by full name (so load order doesn't capture
   the wrong symbol) and guarded on it existing, so MTN still works - unstyled -
   when the parser isn't available (e.g. the ImportString fallback path). *)
applyMathFont[boxes_] := Which[
    (* None / "" / Automatic all keep the FE-native math font - the "TI" math-italic
       style LaTeXMathParse already emits, which is correctly sized relative to body
       text and identical on every machine (issue #45). A named family is the
       explicit Computer-Modern / LaTeX opt-in. *)
    boxes === $Failed || MatchQ[$mathFontFamily, None | "" | Automatic], boxes,
    Names["Wolfram`Parser`LaTeXMathStyle"] === {}, boxes,
    True, Symbol["Wolfram`Parser`LaTeXMathStyle"][boxes, $mathFontFamily]
]

(* Promote a balanced bracketing-bar pair to the front end's Abs / Norm TemplateBox
   (clean non-extensible bars), instead of the raw \[LeftBracketingBar]..
   \[RightBracketingBar] glyphs the parser emits for a bare |x| - which the FE
   auto-sizes into stretched, seamed bars (issue #46, follow-up to #33/#28). Only the
   explicit \lvert / \lVert macros were promoted before (they carry SpanMaxSize -> 1);
   a bare | arrives as a bare glyph, or SpanMinSize -> r when sized to a tall
   argument, so accept all three wrapper forms. Safe because only a genuine modulus
   yields a balanced open(U+F603)+close(U+F604) pair - a conditional P(a|b) is an
   ASCII "|", a bra/ket bar is already absorbed into a Ket/BraKet template - so
   keying on the pair catches exactly the moduli. *)
$openBar   = "\[LeftBracketingBar]"        | StyleBox["\[LeftBracketingBar]", ___]
$closeBar  = "\[RightBracketingBar]"       | StyleBox["\[RightBracketingBar]", ___]
$openDBar  = "\[LeftDoubleBracketingBar]"  | StyleBox["\[LeftDoubleBracketingBar]", ___]
$closeDBar = "\[RightDoubleBracketingBar]" | StyleBox["\[RightDoubleBracketingBar]", ___]
$barSpacer = " " | "\[ThinSpace]" | "\[VeryThinSpace]" | "\[MediumSpace]" | "\[NegativeThinSpace]" | "\[NegativeVeryThinSpace]" | FromCharacterCode[16^^200A]
barContent[parts_List] := With[{c = DeleteCases[parts, $barSpacer]},
    Which[c === {}, "", Length[c] === 1, First[c], True, RowBox[c]]]

(* A norm whose bars never became the PUA bracketing pair - a bare \[DoubleVerticalBar]
   (U+2225, which is ALSO how \parallel is spelled) or a SpanMaxSize -> 1 pinned bar - slips
   past the two rules below, so around a TALL argument (a ket taller than a text line) the
   relational glyph cannot stretch and renders as two one-line ticks (issue #64). Several TeX
   spellings converge on this shape (\|...\| has no matchfix production; a bare-bar ket poisons
   the \lVert..\rVert matchfix). Promote such a pair to Norm as well - straightenTallBars then
   draws it as a scaled full-height rule and NotebookToMarkdown round-trips it to \lVert. Bare
   U+2225 is ambiguous (\parallel vs norm), so three guards carry the distinction: the bars are
   the SAME glyph (matched by one pattern), the argument is TALL (a scalar \|x\| is already
   correct at nominal size and is left alone), and the pair is NOT flanked by an operand - a
   binary relation a || x || c has operands on both outer sides, whereas a delimiter's opener
   follows an operator, an opening bracket, or nothing. *)
$bareDBar = "\[DoubleVerticalBar]" | StyleBox["\[DoubleVerticalBar]", ___]
operandBoxQ[b_] := MatchQ[b, _TemplateBox | _RowBox | _SqrtBox | _FractionBox | _RadicalBox |
        SuperscriptBox[__] | SubscriptBox[__] | SubsuperscriptBox[__] | UnderoverscriptBox[__]] ||
    (StringQ[b] && StringMatchQ[b, (LetterCharacter | DigitCharacter) ..])
normPairUnflankedQ[pre_List, post_List] := With[
    {p = DeleteCases[pre, $barSpacer], q = DeleteCases[post, $barSpacer]},
    (p === {} || ! operandBoxQ[Last[p]]) && (q === {} || ! operandBoxQ[First[q]])
]
templatizeBars[boxes_] := boxes //. {
    RowBox[{pre___, $bareDBar, mid : Except[$bareDBar] .., $bareDBar, post___}] /;
        tallArgQ[barContent[{mid}]] && normPairUnflankedQ[{pre}, {post}] :>
        RowBox[{pre, TemplateBox[{barContent[{mid}]}, "Norm"], post}],
    RowBox[{pre___, $openDBar, mid : Except[$openDBar | $closeDBar] .., $closeDBar, post___}] :>
        RowBox[{pre, TemplateBox[{barContent[{mid}]}, "Norm"], post}],
    RowBox[{pre___, $openBar, mid : Except[$openBar | $closeBar] .., $closeBar, post___}] :>
        RowBox[{pre, TemplateBox[{barContent[{mid}]}, "Abs"], post}]
}

(* The Abs / Norm TemplateBox draws extensible bars; stretched past ~one line height
   around a TALL argument - a braket, whose angle brackets exceed a text line, as in
   |<phi|psi>|^2 - the FE builds the glyph from pieces and it renders with a visible
   mid-height seam. Rewrite only the tall-argument templates to a plain scaled
   vertical line (\[VerticalLine] / \[DoubleVerticalBar], relational glyphs that never
   extend, so never seam); a scalar argument keeps the template (correct at base size,
   round-trips to \lvert / \lVert). Runs OUTSIDE templatizeBars' //. - the vertical
   line is not a bracketing bar, so it is never re-promoted (issue #48). *)
$tallBarScale = 1.3
tallArgQ[arg_] := ! FreeQ[arg, TemplateBox[_, "Ket" | "Bra" | "Braket" | "BraKet"]]
straightBar[glyph_] := StyleBox[glyph, FontSize -> $tallBarScale Inherited]
straightenTallBars[boxes_] := boxes /. {
    TemplateBox[{arg_}, "Abs"] /; tallArgQ[arg] :> RowBox[{straightBar["\[VerticalLine]"], arg, straightBar["\[VerticalLine]"]}],
    TemplateBox[{arg_}, "Norm"] /; tallArgQ[arg] :> RowBox[{straightBar["\[DoubleVerticalBar]"], arg, straightBar["\[DoubleVerticalBar]"]}]
}

texBoxes[math_String] :=
    Block[{r = wolframParserTeX[math]},
        straightenTallBars @ applyMathFont @ templatizeBars @ If[ r =!= $Failed, r, texBoxesViaImport[math] ]
    ]

(* Detection and call both resolve the parser at *runtime* by its full name.
   Two traps this avoids: (1) LaTeXMathParse has only DownValues, so the obvious
   ValueQ[LaTeXMathParse] gate is always False and would reject a perfectly loaded
   parser; (2) an unqualified `LaTeXMathParse` token is captured to whatever
   context is active when this file is read - if the paclet loads later, that
   token names a different (empty) symbol. Symbol["Wolfram`Parser`LaTeXMathParse"]
   always names the real one once the context exists. Success is judged by the
   result being box-like; a parse failure returns ParseError[...]/$Failed, which
   falls through to the ImportString path. *)
wolframParserTeX[math_String] :=
    If[ Names["Wolfram`Parser`LaTeXMathParse"] === {},
        $Failed,
        Module[{m, r},
            (* pre-substitute TeX tokens the parser mishandles: \cdot -> · (else
               it maps to ×, issue #11), \, -> control-space (else literal "\,"
               leaks, issue #13). The cdot guard rejects \cdots (centered ellipsis). *)
            m = StringReplace[math, {
                RegularExpression["\\\\cdot(?![a-zA-Z])"] -> "\[CenterDot]",
                "\\," -> "\\ "
            }];
            r = Quiet @ Check[Symbol["Wolfram`Parser`LaTeXMathParse"][m], $Failed];
            (* Accept whatever boxes the parser returns; only reject its known
               failure shapes. Head is matched by short name so a ParseError from
               the paclet's own context still trips it regardless of how this file
               captured the bare symbol. *)
            If[ MatchQ[r, $Failed | _Failure] || SymbolName[Head[r]] === "ParseError" || ! FreeQ[r, $Failed],
                $Failed,
                r
            ]
        ]
    ]

(* last-resort TeX import (the WolframParser path having failed or being
   absent). ImportString[..., "TeX"] understands no spacing / sizing
   typography, so strip the tokens that would otherwise leak as literal
   text before importing (issue #25): \! negative thin space, the empty
   \left. / \right. delimiters, and the sized-delimiter prefixes
   \big / \Big / \bigg / \Bigg (+ l/r/m variants) - with a word-boundary
   guard so \bigcup / \bigcap / \Bigl-less commands survive. *)
texImportStrip[math_String] := StringReplace[math, {
    "\\!" -> "",
    "\\left." -> "", "\\right." -> "",
    (* the built-in TeX importer maps \hbar to an empty box (it vanishes); \hslash
       imports to the same U+210F glyph (\[HBar]) the primary parser emits and that
       NotebookToMarkdown maps back to \hbar, so swap it in on this fallback (issue #61) *)
    RegularExpression["\\\\hbar(?![a-zA-Z])"] -> "\\hslash",
    RegularExpression["\\\\[Bb]igg?[lrm]?(?![a-zA-Z])"] -> ""
}]
texBoxesViaImport[math_String] :=
    Block[{nb = Quiet @ ImportString["$" <> texImportStrip[math] <> "$", "TeX"]},
        If[ MatchQ[nb, _Notebook],
            FirstCase[nb, Cell[BoxData[b_], ___] :> b, $Failed, Infinity],
            $Failed
        ]
    ]

(* InlineFormula in Default.nb resolves to 1.05*Inherited, which lands inline
   math AND inline code about 1.1x the surrounding Text height (issues #29, #30).
   Pin a relative factor that cancels the inline magnification while tracking
   whatever the host Text style resolves to (so it is not tied to an absolute
   point size); it scales the cell uniformly, keeping sub/superscripts and
   templates in proportion. Display math (mathBlockCell -> DisplayFormula) keeps
   its own prominent size. *)
$inlineFontSize = 0.9 Inherited

(* A bare big operator (indefinite \int, or a limit-less \sum / \prod) comes back
   from LaTeXMathParse as StyleBox[op, FontSize -> 1.7 Inherited] - the lone glyph
   blown up to read as a tall sign, which towers over a short integrand and stretches
   the inline line (issue #47). Dampen it: a restrained inline size, a larger display
   size. Key on the GLYPH, not the factor - sized delimiters (\Big(, \Bigg[) also
   arrive as StyleBox[char, FontSize -> r Inherited] with r up to 3.0 and must keep
   their size; the large-operator characters are disjoint from every delimiter. The
   "> 1.5" guard limits the rewrite to the enlargement, never a deliberately shrunk
   operator. Matched char-by-char so a multi-glyph \iint / \iiint run qualifies. *)
$bigOpGlyphs = {"\[Integral]", "\[ContourIntegral]", "\[DoubleContourIntegral]",
    "\[ClockwiseContourIntegral]", "\[CounterClockwiseContourIntegral]",
    "\[Sum]", "\[Product]", "\[Coproduct]"}
bigOpGlyphQ[s_String] := StringLength[s] > 0 && AllTrue[Characters[s], MemberQ[$bigOpGlyphs, #] &]
$bigOpInlineScale = 1.15
$bigOpDisplayScale = 1.4
dampenBigOps[boxes_, scale_] := boxes /.
    StyleBox[s_String, a___, FontSize -> (r_?NumericQ) Inherited, b___] /; bigOpGlyphQ[s] && r > 1.5 :>
        StyleBox[s, a, FontSize -> scale Inherited, b]

mathInline[math_String] := Block[{boxes = texBoxes[math]},
    If[ boxes === $Failed,
        Cell[BoxData[FormBox[inputBoxes[math], TraditionalForm]], "InlineFormula", FontSize -> $inlineFontSize],
        Cell[BoxData[dampenBigOps[boxes, $bigOpInlineScale]], "InlineFormula", FontSize -> $inlineFontSize]
    ]
]

(* $$ ... $$ on its own line (or fenced across lines) -> a centered "DisplayFormula"
   cell. Stylesheets vary in whether DisplayFormula centers within the cell or
   left-indents it, so wrap the formula in a PaneBox that takes the full cell width
   and centers its content; that way the equation sits horizontally centered the way
   a markdown viewer renders display math, in any stylesheet. *)
mathBlockCell[math_String] := With[{
    boxes = dampenBigOps[Replace[texBoxes[math], $Failed -> FormBox[inputBoxes[math], TraditionalForm]], $bigOpDisplayScale]
},
    Cell[BoxData[PaneBox[boxes, ImageSize -> Full, Alignment -> Center]], "DisplayFormula"]
]

(* the web-deployed resource templates (Function / Paclet / Example / Data
   Repository, Prompt, Demonstration). Their notebooks keep the official resource
   stylesheet - which has NONE of the doc-center typed-link templates (PackageLink /
   RefLink, issue #20) - and their deployed page is plain web HTML where paclet:
   URIs don't resolve. So a symbol reference in one must be a plain Hyperlink to the
   public web URL, not the typed TemplateBox a built doc page (Symbol/Guide/TechNote)
   uses. Doc pages go through DocumentationBuild + the doc center, where both hold. *)
$resourceTemplates = {"FunctionResource", "Paclet", "Example", "Data", "Prompt", "Demonstration"}
resourceTemplateQ[] := MemberQ[$resourceTemplates, $docTemplate]

(* markdown links: [text](paclet:Pub/Name/ref/Sym) -> a reference Link (palette
   "Custom URI"); [text](http...) -> a Hyperlink (palette "Link to URL"). The
   ButtonBox sits directly in the surrounding TextData (a text hyperlink), not
   wrapped in Cell[BoxData[...], "InlineFormula"] - the latter renders the link
   text in code/formula style instead of as an inline prose link.

   A `code`-wrapped label is the explicit "link this symbol" annotation: it renders
   the label in code/formula style as the link, i.e. a reference link the way
   See Also entries look. So [`WCAGContrastRatio`](paclet:.../ref/WCAGContrastRatio)
   is a code-styled symbol link, while [the docs](https://...) is a prose link. *)
linkButton[text_, url_String] := Which[
    (* a resource notebook's stylesheet has none of the doc-center typed-link
       TemplateBoxes (issue #20), so emit a plain reference-Link ButtonBox instead -
       keeping the paclet: target, which the cloud / CloudPublish resolves on the
       deployed page (and which the markdown twin rewrites to a web URL for GitHub) *)
    StringStartsQ[url, "paclet:"] && resourceTemplateQ[],
        ButtonBox[text, BaseStyle -> "Link", ButtonData -> url],
    StringStartsQ[url, "paclet:"],
        pacletLinkBox[text, url], (* issue #20 *)
    True,
        ButtonBox[text, BaseStyle -> "Hyperlink", ButtonData -> {URL[url], None}]
]

(* a linkButton result safe to splice into prose TextData: a bare TemplateBox
   (paclet link) is rejected by Export[..., "NB"] (issue #22, same failure
   class as the RelatedGuides / MoreAbout slot fixes), so wrap it in a
   BoxData InlineFormula cell when it lands in TextData. ButtonBox results
   (hyperlinks) are already TextData-safe and pass through unchanged. *)
textDataLinkBox[b_TemplateBox] := Cell[BoxData[b], "InlineFormula"]
textDataLinkBox[other_] := other

(* link text supports inline emphasis per CommonMark - "[*Title*](u)" should
   render as a link whose visible label is italic, not as a link displaying
   literal asterisks. Strip a single outer "*"/"**"/"***" wrapper and apply
   the corresponding style under the ButtonBox; mixed / nested cases fall
   through to the literal string form. (StringMatchQ would interpret a
   leading/trailing "*" pattern as a wildcard, so we use StringStartsQ /
   StringEndsQ - those treat strings as literals - and reject inner stars
   so "*foo* bar *baz*" does not get incorrectly stripped.) *)
strippedQ[text_String, marker_String] := With[{n = StringLength[marker]},
    StringLength[text] >= 2 n + 1
        && StringStartsQ[text, marker] && StringEndsQ[text, marker]
        && !StringContainsQ[StringTake[text, {n + 1, -n - 1}], "*"]
]
linkButtonStyled[text_String, url_String] := Which[
    strippedQ[text, "***"],
        linkButton[StyleBox[StringTake[text, {4, -4}], "TI", FontWeight -> "Bold"], url],
    strippedQ[text, "**"],
        linkButton[StyleBox[StringTake[text, {3, -3}], FontWeight -> "Bold"], url],
    strippedQ[text, "*"],
        linkButton[StyleBox[StringTake[text, {2, -2}], "TI"], url],
    True, linkButton[text, url]
]

backtickedQ[text_String] := StringMatchQ[text, "`" ~~ ___ ~~ "`"]

(* a bare label is treated as a symbol name when it looks like one - a leading
   letter or "$" followed by letters / digits / context marks. Only used for the
   empty-target inferred form [Name](), so non-symbol prose hyperlinks like
   "[click here]()" still go through unchanged. *)
symbolLikeQ[text_String] := StringMatchQ[text, (LetterCharacter | "$") ~~ (WordCharacter | "$" | "`") ...]

linkInline[text_String, url_String] := Which[
    (* an empty target - [Symbol]() (canonical) or the legacy [`Symbol`]() form -
       infers the reference. The backtick wrapping is purely decorative here, so
       both render identically; bare prose labels with an empty target are left
       as literal text. *)
    url === "" && backtickedQ[text], linkInferred[StringTake[text, {2, -2}]],
    url === "" && symbolLikeQ[text], linkInferred[text],
    url === "", unescapeMarkdownPunctuation[text],
    (* a `code`-wrapped label is a code-styled reference link; backslash escapes
       inside the backticks are literal, so the stripped content is used as-is. *)
    backtickedQ[text], Cell[BoxData @ linkButton[StringTake[text, {2, -2}], url], "InlineFormula"],
    (* a plain label is an ordinary prose hyperlink; markdown's \<punct> escapes
       in the label (e.g. "[Wolfram\`Parser\`](paclet:...)") unescape before the
       ButtonBox so the displayed text doesn't keep the literal backslashes.
       linkButtonStyled additionally honours a single layer of *...* / **...**
       emphasis around the label. *)
    True, textDataLinkBox @ linkButtonStyled[unescapeMarkdownPunctuation[text], url]
]

(* the ref-page URI a bare symbol name resolves to: a name in the documented
   paclet's context links to its paclet ref page, a System symbol to its system
   ref page; anything else does not resolve. *)
inferURL[name_String] := With[{pkg = packagePath[$docPaclet, $docContext]}, Which[
    symbolInDocQ[name] && pkg =!= "", "paclet:" <> pkg <> "/ref/" <> name, (* issue #23 *)
    symbolInDocQ[name], "paclet:ref/" <> name,
    symbolInContextQ[name, "System`"], "paclet:ref/" <> name,
    True, None
]]

(* the public web URL a bare symbol name resolves to. Mirrors inferURL but for the
   GitHub-renderable twin: paclet symbols point at their PacletRepository page, System
   symbols at the Wolfram Language reference site. *)
inferWebURL[name_String] := Which[
    symbolInDocQ[name] && $docPaclet =!= "",
        "https://resources.wolframcloud.com/PacletRepository/resources/" <> $docPaclet <> "/ref/" <> name,
    symbolInContextQ[name, "System`"],
        "https://reference.wolfram.com/language/ref/" <> name <> ".html",
    True, None
]

(* translate a "paclet:..." URI (the notebook's internal link target) to the public
   web URL of the same ref/guide/tutorial. Used when serialising the markdown twin
   so the rendered page has working links on GitHub. *)
pacletToWebURL[uri_String] := Block[{rest = StringTrim[uri], paclet, kind, name, parts},
    rest = StringDelete[rest, StartOfString ~~ "paclet:"];
    parts = StringSplit[rest, "/"];
    Which[
        Length[parts] === 2 && MemberQ[{"ref", "guide", "tutorial"}, parts[[1]]],
            "https://reference.wolfram.com/language/" <> parts[[1]] <> "/" <> parts[[2]] <> If[parts[[1]] === "ref", ".html", ""],
        Length[parts] >= 3 && MemberQ[{"ref", "guide", "tutorial"}, parts[[-2]]],
            paclet = StringRiffle[parts[[;; -3]], "/"];
            kind = parts[[-2]]; name = parts[[-1]];
            "https://resources.wolframcloud.com/PacletRepository/resources/" <> paclet <> "/" <> kind <> "/" <> name,
        True, "paclet:" <> rest
    ]
]

(* rewrite inferred and paclet-scheme links in a prose run to their public web URLs
   for the GitHub-renderable twin. The notebook keeps the paclet: targets unchanged
   (linkInferred / linkInline). Three forms get expanded:
     [`Symbol`]            (bare inferred)         -> [`Symbol`](https://...)
     [`Symbol`]()          (explicit empty)        -> [`Symbol`](https://...)
     [label](paclet:...)   (explicit paclet URI)   -> [label](https://...)
   Unresolvable symbols (not in $docContext or System`) and non-paclet URLs are left
   alone, so a stray "[`SomeRandomThing`]" passes through unchanged. *)
resolveWebRefs[text_String] := Block[{s = text, resolveLink},
    (* step 1: normalise the legacy [`X`] without parens to [`X`]() so the inferred
       URL resolves uniformly with the canonical [`X`]() / [X]() forms. *)
    s = StringReplace[s, RegularExpression["\\[`([^`\\n]+)`\\](?!\\()"] -> "[`$1`]()"];
    (* step 2: rewrite every inferred link [label](url) where label is either bare
       (the canonical form) or backtick-wrapped (the legacy form). For an empty url
       look up the web URL from the bare symbol name; for "paclet:..." translate to
       the public web URL. *)
    resolveLink[sym_, url_] := Which[
        StringStartsQ[url, "paclet:"], pacletToWebURL[url],
        url === "", With[{w = inferWebURL[sym]}, If[w === None, "", w]],
        True, url
    ];
    s = StringReplace[s, {
        "[`" ~~ sym : Shortest[Except["`" | "\n"] ..] ~~ "`](" ~~ url : Shortest[Except[")"] ...] ~~ ")" :>
            "[`" <> sym <> "`](" <> resolveLink[sym, url] <> ")",
        "[" ~~ sym : Shortest[Except["]" | "`" | "\n"] ..] ~~ "](" ~~ url : Shortest[Except[")"] ...] ~~ ")" :>
            "[" <> sym <> "](" <> resolveLink[sym, url] <> ")"
    }];
    s
]

(* an "empty" backtick link [`Name`] (brackets, no URL) is the convenient symbol
   annotation: infer the ref URL from the name and render a code-styled reference
   link, the way auto-linking used to. Linking only ever happens on backticked
   content - a bare [Name] is left as literal text. If the name does not resolve,
   fall back to plain inline code. *)
linkInferred[name_String] := Block[{url = inferURL[name]},
    Which[
        url === None, codeToInline[name],
        (* resource notebook: the plain reference-Link ButtonBox the Function/Paclet
           Repository templates use (FunctionResource`Information`insertButtonData) -
           BaseStyle "Link" + the paclet:ref target kept. The doc-center typed
           PackageLink/RefLink TemplateBox of issue #20 is doc-page-only. *)
        resourceTemplateQ[],
            Cell[BoxData @ ButtonBox[name, BaseStyle -> "Link", ButtonData -> url], "InlineFormula"],
        True, Cell[BoxData @ pacletLinkBox[name, url], "InlineFormula"] (* issue #20 *)
    ]
]

(* CommonMark parses links before emphasis - in "*Continue [*Title*](url)*"
   the link binds tighter than the surrounding "*...*" italic, so the inner
   "*"s belong to the link text, not to the outer emphasis. A single-pass
   StringSplit with both italic and link in its alternative list does the
   wrong thing: italic at the leading "*" wins by leftmost position and
   eats forward past the link's "[", breaking the link into pieces.

   Fix: pre-extract every link / image to a sentinel placeholder before the
   emphasis split runs. The stash sits in Block-dynamic $inlineLinkBoxes so
   the recursive emWith re-entry from nested emphasis still resolves the
   parent's placeholders. The core split's sentinel rule splices each link
   box back at its original position. *)
$inlineLinkBoxes = {}

(* Decode HTML/XML character references in prose: numeric refs - decimal
   "&#9673;" and hex "&#x25C9;" - become the literal Unicode glyph; a small set
   of named entities is mapped too (an unrecognised "&word;" is left untouched).
   Applied to plain-text runs (after span/emphasis splitting, so a decoded "<" or
   "_" from "&lt;" / "&#95;" can no longer spawn markup) and to <code> content. *)
$namedEntities = <|
    "amp" -> "&", "lt" -> "<", "gt" -> ">", "quot" -> "\"", "apos" -> "'",
    "nbsp" -> "\[NonBreakingSpace]", "ndash" -> "\[Dash]", "mdash" -> "\[LongDash]",
    "hellip" -> "\[Ellipsis]", "times" -> "\[Times]", "deg" -> "\[Degree]",
    "rarr" -> "\[RightArrow]", "larr" -> "\[LeftArrow]", "harr" -> "\[LeftRightArrow]"
|>;
decodeEntities[s_String] := StringReplace[s, {
    "&#x" ~~ h : (HexadecimalCharacter ..) ~~ ";" :> FromCharacterCode[FromDigits[h, 16]],
    "&#" ~~ d : (DigitCharacter ..) ~~ ";" :> FromCharacterCode[FromDigits[d, 10]],
    "&" ~~ name : (LetterCharacter ..) ~~ ";" :> Lookup[$namedEntities, name, "&" <> name <> ";"]
}]

inlineTextData[text_String] := Block[{$inlineLinkBoxes = {}}, inlineTextDataCore[text]]

inlineTextDataCore[text_String] := Module[{prep, stash},
    stash = Function[box,
        AppendTo[$inlineLinkBoxes, box];
        "\:f8f5" <> IntegerString[Length[$inlineLinkBoxes]] <> "\:f8f6"
    ];
    prep = StringReplace[text, {
        (* literal-content spans first: their inner text is verbatim and
           must survive the backslash mask / link extraction below
           untouched (e.g. "<code>\[CircleTimes]</code>" - the named-char
           escape lives inside the code span and the mask rule below would
           otherwise eat the leading backslash). StringReplace picks the
           leftmost match position, so a "<code>...</code>" starting at an
           earlier offset wins over a backslash mask that would otherwise
           fire deeper inside the span. *)
        "<code>" ~~ inner : Shortest[__] ~~ "</code>" :> stash[codeInlineCell[inner]],
        "``" ~~ c : Shortest[__] ~~ "``" :> stash[literalCodeInline[c]],
        "`" ~~ c : Shortest[__] ~~ "`" :> stash[codeToInline[c]],
        "$$" ~~ m : Shortest[Except["$"] ..] ~~ "$$" :> stash[mathInline[m]],
        "$" ~~ m : Shortest[Except["$"] ..] ~~ "$" :> stash[mathInline[m]],
        (* mask "\[" / "\!" so neither triggers the link / image patterns;
           any other "\X" escape passes through here and is handled by the
           normal punctuation-escape rule in the main split. *)
        "\\" ~~ c : ("[" | "!") :> "\:f8fb" <> c,
        (* image (leading "!") matched before link, same as the original
           single-pass order. *)
        "![" ~~ a : Shortest[Except["]"] ...] ~~ "](" ~~ u : Shortest[Except[")"] ..] ~~ ")" :> stash[inlineImage[a, u]],
        (* allow an empty URL "[`Symbol`]()" - the pandoc / GitHub-renderable
           inferred form (an empty link is at least a recognisable link element in
           markdown viewers); linkInline routes it to linkInferred. The bare
           "[`Symbol`]" without parens is *not* auto-linked: that follows strict
           markdown semantics ("[X]" alone is literal bracketed text) and avoids
           surprising linkifying of expressions like "[`Import`]["doc.md"]" where
           the author wanted only inline code. *)
        "[" ~~ t : Shortest[Except["]"] ..] ~~ "](" ~~ u : Shortest[Except[")"] ...] ~~ ")" :> stash[linkInline[t, u]]
    }];
    Replace[
        (* underscore emphasis runs last, on the plain-text runs the main split leaves
           behind, so its word-boundary check never sees code / link / math content. *)
        Replace[
            StringSplit[prep, {
                (* restore pre-extracted link / image / code / math boxes at
                   their original positions. Highest priority so emphasis
                   cannot reach across the placeholder. *)
                "\:f8f5" ~~ idx : DigitCharacter .. ~~ "\:f8f6" :> $inlineLinkBoxes[[FromDigits[idx]]],
                (* restore "\[" / "\!" mask as the literal char *)
                "\:f8fb" ~~ c : ("[" | "!") :> c,
                (* other backslash escapes (handled here, not in pre-extraction,
                   so they do not corrupt code / math content) *)
                "\\" ~~ c : PunctuationCharacter :> c,
                "~~" ~~ s : Shortest[__] ~~ "~~" :> emStrikeBox[s],
                (* portable subscript "H<sub>2</sub>O" and superscript "2<sup>10</sup>" -
                   HTML tags renderers agree on. The single-tilde / single-caret Pandoc
                   shorthands ("H~2~O", "2^10^") are accepted too; listed after "~~" so
                   strikethrough wins at a doubled-tilde position. *)
                "<sub>" ~~ s : Shortest[Except["<"] ..] ~~ "</sub>" :> proseSubBox[s],
                "<sup>" ~~ s : Shortest[Except["<"] ..] ~~ "</sup>" :> proseSupBox[s],
                "~" ~~ s : Shortest[Except["~"|" "] ..] ~~ "~" :> proseSubBox[s],
                "^" ~~ s : Shortest[Except["^"|" "] ..] ~~ "^" :> proseSupBox[s],
                "***" ~~ s : Shortest[__] ~~ "***" :> emBoldItalicBox[s],
                "**" ~~ s : Shortest[__] ~~ "**" :> emBoldBox[s],
                (* *word* -> italic: the StyleBox["TI"] form usage descriptions mark
                   arguments with (not a formula cell) *)
                Verbatim["*"] ~~ i : (Except["*"] ..) ~~ Verbatim["*"] :> emItalicBox[i]
            }],
            s_String :> Sequence @@ underscoreEm[s],
            {1}
        ],
        (* a literal "..." in prose should be the single ellipsis character (the
           notebook analysis flags three dots); only the plain-text runs are touched. *)
        s_String :> decodeEntities @ StringReplace[s, "..." -> "\[Ellipsis]"],
        {1}
    ]
]

(* a Symbol page's "## Usage" prose, rendered as one Usage cell with its inline
   formatting. Backticked spans inside a usage line are signatures and argument
   references, so route them through templateBox (which italicises args and turns
   "~i~" into a subscript) instead of the literal codeToInline used elsewhere. *)
usageCell[rawUsage_String] := Block[{
    codeToInline = Function[c, Cell[BoxData[stripLinks @ templateBox[c]], "InlineFormula"]]
},
    Cell[
        TextData @ Prepend[inlineTextData[StringTrim[rawUsage]], Cell["   ", "ModInfo"]],
        "Usage"
    ]
]

(* a GitHub-flavored pipe table -> the same GridBox the palette inserts via
   "Insert Custom Table" / "2 Column" / "3 Column": outer style
   NColumnTableMod, with each row prefixed by a fixed Cell["      ", "ModInfo"]
   placeholder (the narrow modification-indicator column, always whitespace -
   NOT a slot for col-1 content) and the N content cells styled TableText.
   The cell style supplies dividers / alignment / spacing, so no inline
   GridBox options are needed. ONLY emitted when the document is a paclet
   documentation page (Symbol / Guide / TechNote / Overview), where the
   stylesheet defines 2ColumnTableMod / 3ColumnTableMod / ModInfo / TableText.
   The resource definition-notebook stylesheets (FunctionResource / Paclet /
   Example / Data / Prompt / Demonstration / LLMTool) do NOT define those
   styles - rendering an *TableMod cell there leaks unstyled / wrong-looking
   tables. For those templates we fall through to the generic GridBox path
   with the TableNotes / Text cell wrapper that has always shipped. *)
$tableModTemplates = {"Symbol", "Guide", "TechNote", "Overview", "Chapter", "BookChapter", "ComputationalEssay", "Essay", "Default",
    "Format", "ServiceConnection", "Device", "Interpreter", "Entity", "Character", "Message", "Program", "Workflow", "WorkflowGuide"}

tableModStyleFor[2] /; MemberQ[$tableModTemplates, $docTemplate] := "2ColumnTableMod"
tableModStyleFor[3] /; MemberQ[$tableModTemplates, $docTemplate] := "3ColumnTableMod"
tableModStyleFor[_] := None

modInfoPlaceholder = Cell["      ", "ModInfo"];

tableModRow[cells_List, ncol_Integer, opts___] := Prepend[
    Cell[TextData @ inlineTextData[#], "TableText", opts] & /@ PadRight[cells, ncol, ""],
    modInfoPlaceholder
]

(* Fallback for templates / widths the palette has no *TableMod style for.
   "TableNotes" is the table style the Function Repository / Paclet / Example
   definition-notebook docked cells insert, and exists in those stylesheets.
   The documentation stylesheets (Symbol / Guide / TechNote) and Default.nb
   do not define it, so a "TableNotes" cell renders unstyled / cramped there
   - switch to "Text" for those, which exists everywhere. *)
tableCellBox[text_String, opts___] := Cell[TextData @ inlineTextData[text], "TableText", opts]

tableGridRow[cells_List, ncol_Integer, opts___] :=
    tableCellBox[#, opts] & /@ PadRight[cells, ncol, ""]

$tableCellStyleFor := If[resourceTemplateQ[], "TableNotes", "Text"]

(* a pipe table renders as a *TableMod cell when the doc template's
   stylesheet defines them (paclet documentation pages, ncol = 2 or 3);
   otherwise (resource definition notebooks, or wider tables) it falls
   through to a generic GridBox with inline dividers and the
   $tableCellStyleFor-picked outer cell style. *)
tableCell[block_] := Block[{ncol = Length[block["Header"]], modStyle = tableModStyleFor[Length[block["Header"]]], rows},
    If[modStyle =!= None,
        rows = Join[
            {tableModRow[block["Header"], ncol, FontWeight -> Bold]},
            tableModRow[#, ncol] & /@ block["Rows"]
        ];
        Cell[BoxData[GridBox[rows]], modStyle]
        ,
        rows = Join[
            {tableGridRow[block["Header"], ncol, FontWeight -> Bold]},
            tableGridRow[#, ncol] & /@ block["Rows"]
        ];
        Cell[BoxData[GridBox[rows,
            GridBoxAlignment -> {"Columns" -> {{Left}}, "Rows" -> {{Baseline}}},
            GridBoxDividers -> {"Columns" -> {{None}}, "Rows" -> {{True}}},
            GridBoxSpacings -> {"Columns" -> {{1.5}}, "Rows" -> {{0.7}}}
        ]], $tableCellStyleFor]
    ]
]

(* an inlined markdown image (![alt](path "title")) -> an image cell. The title is
   a *raw cell style* override (a "Text" style cell will not render its graphic on
   the deployed cloud page, so the default is "Output", the style the evaluated
   example images use); a documentation image wants "ExampleImage". The special
   title "papertear" keeps the "Output" style and adds the front end's Paper Tear
   background. *)
imageCell[block_] := With[{title = StringTrim @ Lookup[block, "Effect", ""]},
    Which[
        ToLowerCase[title] === "papertear",
            Cell[BoxData[ToBoxes @ block["Image"]], "Output", BackgroundAppearance -> "PaperTear"],
        title =!= "",
            Cell[BoxData[ToBoxes @ block["Image"]], title],
        True,
            Cell[BoxData[ToBoxes @ block["Image"]], "Output"]
    ]
]

(* fill the visible Categorization section cells (Entity Type / Paclet Name /
   Context / URI) from the frontmatter, keyed by their CellLabel. *)
fillCategorization[nb_, type_String, meta_] := Block[{
    vals = <|
        "Entity Type" -> type,
        "Paclet Name" -> Lookup[meta, "Paclet", ""],
        "Context" -> Lookup[meta, "Context", ""],
        "URI" -> Lookup[meta, "URI", ""]
    |>,
    filled, hasURI
},
    filled = nb /. Cell[c_, "Categorization", o___] :> With[{lbl = CellLabel /. Flatten[{o}]},
        If[ KeyExistsQ[vals, lbl] && vals[lbl] =!= "",
            Cell[vals[lbl], "Categorization", o],
            Cell[c, "Categorization", o]
        ]
    ];
    (* the base templates have no URI row; append one to the section *)
    hasURI = ! FreeQ[filled, Cell[_, "Categorization", a___] /; (CellLabel /. Flatten[{a}]) === "URI"];
    If[ vals["URI"] =!= "" && ! hasURI,
        filled = filled /. Cell[CellGroupData[{sec : Cell[_, "CategorizationSection", ___], body___}, st_], go___] :>
            Cell[CellGroupData[{sec, body, Cell[vals["URI"], "Categorization", CellLabel -> "URI"]}, st], go]
    ];
    filled
]

(* doc templates evaluate each example unit independently - default
   CellContext to CellGroup so example state does not leak between units /
   sections; honor a frontmatter "CellContext" override (issue #19).
   Bare-symbol names "CellGroup" / "Notebook" / "InheritFromParent" map
   to the corresponding symbol; anything else passes through as a literal
   context string (e.g. `"Global`"`). *)
$docCellContextDefault = <|"Symbol" -> CellGroup, "Guide" -> CellGroup, "Tech Note" -> CellGroup, "Tutorial" -> CellGroup,
    (* the reference subtypes + workflow pages (setDocMetadata is keyed by the
       Categorization entity-type string, not the Template name) *)
    "Format" -> CellGroup, "Service Connection" -> CellGroup, "Device Connection" -> CellGroup,
    "Interpreter" -> CellGroup, "Entity" -> CellGroup, "Character Name" -> CellGroup,
    "Message" -> CellGroup, "Program" -> CellGroup, "Workflow" -> CellGroup, "Workflow Guide" -> CellGroup|>
parseCellContextValue[v_Symbol] := v
parseCellContextValue[s_String] := Switch[StringTrim[s],
    "CellGroup", CellGroup,
    "Notebook", Notebook,
    "InheritFromParent", InheritFromParent,
    _, StringTrim[s]
]
parseCellContextValue[other_] := other

setDocMetadata[Notebook[cells_, o : OptionsPattern[]], meta_, type_String] := Block[{opts = Flatten[{o}], md, tr, cc},
    md = {
        "title" -> Lookup[meta, "Name", Lookup[meta, "Title", ""]],
        "context" -> Lookup[meta, "Context", ""],
        "keywords" -> asList @ Lookup[meta, "Keywords", {}],
        "summary" -> Lookup[meta, "Description", ""],
        "paclet" -> Lookup[meta, "Paclet", ""],
        "uri" -> Lookup[meta, "URI", ""],
        "type" -> type,
        "index" -> True,
        "language" -> "en"
    };
    tr = Lookup[opts, TaggingRules, {}];
    tr = If[ ListQ[tr], Append[DeleteCases[tr, "Metadata" -> _], "Metadata" -> md], {"Metadata" -> md} ];
    cc = If[ KeyExistsQ[meta, "CellContext"],
        parseCellContextValue[meta["CellContext"]],
        Lookup[$docCellContextDefault, type, Automatic]
    ];
    Notebook[cells, TaggingRules -> tr,
        Sequence @@ If[cc === Automatic, {}, {CellContext -> cc}],
        Sequence @@ DeleteCases[opts, _[TaggingRules | CellContext, _]]
    ]
]

(* markdown example-taxonomy sections -> the symbol page's ExampleSection titles
   ("Requirements" is NOT an ExampleSection on the Symbol template - it only
   surfaces on FunctionResource / Paclet via examplesSlot / exampleNotebookSlot,
   which generate fresh Subsection cells per $exampleOrder entry.) *)
$extendedTitles = <|
    "scope" -> "Scope",
    "generalizations and extensions" -> "Generalizations & Extensions",
    "options" -> "Options",
    "applications" -> "Applications",
    "properties and relations" -> "Properties & Relations",
    "possible issues" -> "Possible Issues",
    "neat examples" -> "Neat Examples"
|>

extendedExampleCells[sectionBlocks_] := exampleContent[sectionBlocks, "ExampleText"]

(* populate the "More Examples" scaffold: each ExampleSection title is an
   InterpretationBox counter cell (it resets In[]/Out[] numbering). For sections
   we have content for, wrap the counter cell + content in an Open CellGroupData;
   sections absent from the markdown are kept heading-only (the counter cell in a
   Closed group) so every standard example section is present and in canonical
   template order, empty if absent - rather than dropped. The XXXX placeholders
   the template ships inside each section were already removed upstream (see the
   XXXX strip in symbolNotebook), so a kept-empty section is just its heading. *)
fillExtendedExamples[nb_, sections_] := Block[{content},
    content = Association @ Map[
        $extendedTitles[#] -> extendedExampleCells[Lookup[sections, #, {}]] &,
        Select[Keys[$extendedTitles], KeyExistsQ[sections, #] &]
    ];
    content = Select[content, # =!= {} &];
    nb /. {
        Cell[CellGroupData[{cnt : Cell[BoxData[InterpretationBox[Cell[title_String, "ExampleSection", ___], _]], "ExampleSection", ___], ___}, _], ___] :>
            With[{c = Lookup[content, title, {}]},
                If[c === {}, Cell[CellGroupData[{cnt}, Closed]], Cell[CellGroupData[Prepend[c, cnt], Open]]]],
        cnt : Cell[BoxData[InterpretationBox[Cell[title_String, "ExampleSection", ___], _]], "ExampleSection", ___] :>
            With[{c = Lookup[content, title, {}]},
                If[c === {}, Cell[CellGroupData[{cnt}, Closed]], Cell[CellGroupData[Prepend[c, cnt], Open]]]]
    }
]

(* Wrap PrimaryExamplesSection + the basic examples into one CellGroupData, the
   shape a hand-authored / DocumentationBuild-ready ref page uses (every other
   top-level section is already a group; only PrimaryExamplesSection comes flat
   from the editing template). The More-Examples scaffold stays a sibling group,
   as in a real source page. Without this the build cannot tell where Basic
   Examples ends and scatters the trailing examples onto the next section. *)
sectionGroupQ[c_] := MatchQ[c, Cell[CellGroupData[{Cell[_, s_String /; StringEndsQ[s, "Section"], ___], ___}, _], ___]]
groupPrimaryExamples[Notebook[cells_List, o___]] := Notebook[groupPrimaryExamples[cells], o]
groupPrimaryExamples[cells_List] := Module[{i, j, nxt},
    i = FirstPosition[cells, Cell[_, "PrimaryExamplesSection", ___], Missing[], {1}];
    If[ MissingQ[i], Return[cells] ];
    i = First[i];
    If[ sectionGroupQ[cells[[i]]], Return[cells] ];   (* already grouped *)
    (* wrap up to just before the next top-level section group (the
       ExtendedExamplesSection / Metadata group), leaving it a sibling *)
    nxt = FirstPosition[Drop[cells, i], _?sectionGroupQ, Missing[], {1}];
    j = If[MissingQ[nxt], Length[cells], i + First[nxt] - 1];
    If[ j < i, Return[cells] ];
    Join[cells[[;; i - 1]], {Cell[CellGroupData[cells[[i ;; j]], Open]]}, cells[[j + 1 ;;]]]
]
groupPrimaryExamples[other_] := other

symbolNotebook[data_] := Block[{meta = data["meta"], sections = data["sections"], nb, name, usagePairs, notes, basicCells, raw},
    nb = docTemplate["FunctionBaseTemplateExt.nb"];
    name = Lookup[meta, "Name", ""];
    (* one Usage cell for the whole ## Usage section - the palette's Double
       Usage Line recipe (Cell[..., "Usage"] containing ModInfo + InlineFormula
       + text per usage line, all lines separated by "\n" inside the single
       cell). The Symbol template ships with a single Usage placeholder cell;
       replace it. Fall back to a whole-text usageCell when the prose does
       not parse into signature+description pairs (e.g. no recognisable head
       before the args). *)
    usagePairs = usageLines[sections];
    notes = detailsCells[sections];
    nb = fillDocString[nb, "ObjectName", name];
    Which[
        usagePairs =!= {},
            nb = nb /. Cell[_, "Usage", ___] :> usageMultiCell[usagePairs],
        (raw = rawSectionText[sections, "usage"]) =!= "",
            nb = nb /. Cell[_, "Usage", ___] :> usageCell[raw]
    ];
    If[ notes =!= {},
        nb = nb /. Cell[_, "Notes", ___] :> Sequence @@ notes
    ];
    (* fill the ExampleInitialization cell with a Needs[] for every documented
       context (Context + ContextPath) so a reader can run the examples. The
       template's ExamplesInitializationSection is kept as-is - it is the standard
       Examples-Initialization section every built ref page has (e.g. LeanLink), and
       DocumentationBuild folds it into the Examples section at build time. *)
    If[ docContextList[meta] =!= {},
        nb = nb /. Cell[_, "ExampleInitialization", o___] :> Cell[BoxData[inputBoxes[exampleInitCode[meta]]], "ExampleInitialization", o]
    ];
    (* walk Basic Examples block-by-block so per-cell `:`-terminated
       captions become ExampleText cells, `---` thematic breaks become
       ExampleDelimiter cells (resetting the In[]/Out[] counter), and
       `### Heading` becomes an ExampleSubsection - the same authoring
       contract docs/examples.md states for every example section. The
       extended sections (Scope/Options/...) already go through
       exampleContent; the Symbol template's Basic Examples slot used to
       flatten via rawSectionText + docExampleCells, which dropped all
       of that structure (see issue #3). *)
    basicCells = exampleContent[Lookup[sections, "basic examples", {}], "ExampleText"];
    (* the base template leaves PrimaryExamplesSection empty for the author;
       insert the basic examples right after its header *)
    If[ basicCells =!= {},
        nb = nb /. Cell[ph_, "PrimaryExamplesSection", o___] :> Sequence[Cell[ph, "PrimaryExamplesSection", o], Sequence @@ basicCells]
    ];
    With[{paclet = Lookup[meta, "Paclet", ""], sa = asList @ Lookup[meta, "SeeAlso", {}], ma = asList @ Lookup[meta, "RelatedGuides", {}]},
        If[ sa =!= {} && paclet =!= "", nb = nb /. Cell[_, "SeeAlso", ___] :> linkRowCell[sa, "SeeAlso", paclet, "ref"] ];
        If[ ma =!= {} && paclet =!= "", nb = nb /. Cell[_, "MoreAbout", ___] :> linkRowCell[ma, "MoreAbout", paclet, "guide"] ]
    ];
    (* drop unfilled placeholders, including dangling FunctionPlaceholder links *)
    nb = nb /. {
        Cell["XXXX", _, ___] :> Nothing,
        Cell[BoxData["XXXX"], _, ___] :> Nothing,
        Cell[c_, _, ___] /; ! FreeQ[c, FrameBox["XXXX"]] :> Nothing
    };
    (* extended example sections (Scope/Options/...): each "More Examples" entry
       is an InterpretationBox counter cell that resets the In[]/Out[] numbering;
       wrap the ones we have content for in a CellGroupData with that content, and
       drop the empty ones (built pages omit empty sections - leaving the XXXX
       ExampleSubsection placeholders or bare counters makes the build fail). *)
    nb = fillExtendedExamples[nb, sections];
    nb = groupPrimaryExamples[nb];
    setDocMetadata[fillCategorization[nb, "Symbol", meta], meta, "Symbol"]
]

(* a listing symbol is a built-in when it resolves to a System` symbol AND the
   paclet does not (re)define it. The paclet guard uses a FULLY-QUALIFIED lookup and
   only applies when $docContext is a real context - "$docContext<>name" with an
   empty (or non-context) $docContext would resolve through $ContextPath and match
   the System symbol itself, falsely marking every built-in as paclet-defined. *)
builtinSymbolQ[name_String] := Names["System`" <> name] =!= {} &&
    (! StringEndsQ[$docContext, "`"] || Names[$docContext <> name] === {})

(* the palette's "Inline Listing": a function-name chip linking to its ref page,
   the same typed link the Documentation Tools button produces (issue #20). A
   built-in links to the SYSTEM reference page "paclet:ref/Sym" (with an italic
   label so the listing reads paclet-vs-built-in at a glance); a paclet symbol
   links to the paclet's own ref page. The kind is inferred from context - there is
   no marker to read. *)
guideFnChip[name_String, paclet_String] := With[
    {pkg = packagePath[paclet, $docContext]},
    Cell[
        BoxData @ If[ builtinSymbolQ[name],
            pacletLinkBox[StyleBox[name, FontSlant -> "Italic"], "paclet:ref/" <> name],
            pacletLinkBox[name, "paclet:" <> If[pkg === "", paclet, pkg] <> "/ref/" <> name]
        ],
        "InlineGuideFunction", TaggingRules -> {"PageType" -> "Function"}
    ]
]

(* a "## Functions" list item "`Sym` description" -> the docked "1-Line Function"
   template: a GuideText cell of TextData[{<chip>, " \[LongDash] ", <description>}],
   the chip linked to the symbol's ref page and the description rendered inline.
   The \[LongDash] separator is canonical and always inserted, so an authored
   dash after the symbol ("- `Sym` \[Dash] description") is stripped first -
   both authored forms render identically instead of doubling the dash. A
   plain hyphen is only treated as the separator when followed by whitespace,
   so a description starting with a hyphenated token survives. *)
stripLeadingDash[s0_String] := Block[{s = StringTrim[s0]},
    Which[
        StringStartsQ[s, "\[LongDash]" | "\[Dash]" | "\[HorizontalLine]"], StringTrim @ StringDrop[s, 1],
        StringStartsQ[s, "--" ~~ WhitespaceCharacter], StringTrim @ StringDrop[s, 2],
        StringStartsQ[s, "-" ~~ WhitespaceCharacter], StringTrim @ StringDrop[s, 1],
        True, s
    ]
]

(* the leading code span of a "## Functions" item -> {{name, note}, rest}. Accepts
   the bare "`Sym`" and the markdown-emphasis "*`Sym`*" form (the "*" wrappers are
   just stripped). A trailing parenthetical right after the span - any "(...)", the
   authored "(WL)" cue among them - is captured VERBATIM as `note` (never
   interpreted; the symbol's kind is inferred from context), and pulling it off the
   front is what lets a comma run continue through "`A` (WL), `B` (WL), ...". *)
guideSymbolSpan[s_String] := Module[{m, name, rest, paren},
    m = StringCases[s, {
        StartOfString ~~ "*`" ~~ n : Shortest[__] ~~ "`*" ~~ t___ :> {n, t},
        StartOfString ~~ "`" ~~ n : Shortest[__] ~~ "`" ~~ t___ :> {n, t}
    }, 1];
    If[m === {}, Return[{}]];
    {name, rest} = First[m];
    paren = StringCases[rest,
        StartOfString ~~ p : (WhitespaceCharacter ... ~~ "(" ~~ Shortest[Except[")"] ...] ~~ ")") ~~ t___ :> {p, t}, 1];
    If[paren === {}, {{{name, ""}, rest}}, {{{name, paren[[1, 1]]}, paren[[1, 2]]}}]
]
guideLeadingSymbols[item_String] := Block[{rest = StringTrim[item], syms, m, afterComma},
    m = guideSymbolSpan[rest];
    If[m === {}, Return[{{}, item}]];
    syms = {m[[1, 1]]}; rest = m[[1, 2]];
    While[True,
        (* ", `C`" extends the run; so does the Oxford-style ", and `C`" / " and `C`" *)
        afterComma = StringCases[rest,
            StartOfString ~~ WhitespaceCharacter ... ~~
                (("," ~~ WhitespaceCharacter ... ~~ RepeatedNull["and" ~~ WhitespaceCharacter .., 1]) |
                 ("and" ~~ WhitespaceCharacter ..)) ~~ t___ :> t, 1];
        If[afterComma === {}, Break[]];
        m = guideSymbolSpan[First[afterComma]];
        If[m === {}, Break[]];
        AppendTo[syms, m[[1, 1]]]; rest = m[[1, 2]]
    ];
    {syms, rest}
]

guideFunctionItem[item_String, paclet_String] := Block[{syms, rest, desc, chips},
    {syms, rest} = guideLeadingSymbols[item];
    If[ syms === {},
        Return @ Cell[TextData @ inlineTextData[item], "GuideText"]
    ];
    desc = stripLeadingDash[rest];
    (* each entry is {name, note}: the context-linked chip followed by its verbatim
       parenthetical note (e.g. " (WL)"), units joined by ", " *)
    chips = Flatten[
        Riffle[
            (With[{nm = First[#], note = Last[#]},
                If[note === "", {guideFnChip[nm, paclet]}, {guideFnChip[nm, paclet], note}]] &) /@ syms,
            ", "],
        1];
    Cell[
        TextData @ If[desc === "", chips,
            Join[chips, {" \[LongDash] "}, inlineTextData[desc]]],
        "GuideText"
    ]
]

(* === guide-to-guide links that build the documentation hierarchy ===
   DocumentationBuild's ComputeLinkTrails assembles the navigation /
   collapsible-sidebar parent-child graph by scanning each guide notebook
   (PageLinks) for ButtonBox links whose ButtonData is a "paclet:.../guide/Name"
   URI - and ONLY inside GuideFunctionsSection / GuideFunctionsSubsection /
   GuideTOCLink / TOCChapter cells (it deletes GuideText, and in the default
   include -> None build also GuideMoreAbout / RelatedGuides). A TemplateBox
   "RefLinkPlain" - what an inline [Name](paclet:.../guide/Name) reference
   renders as - is NOT a ButtonBox and never registers. So a hub guide that
   points to sub-guides must emit the scanned ButtonBox-in-kept-cell form, which
   these helpers build. *)
guideNavButtonBox[label_String, uri_String] := ButtonBox[label, BaseStyle -> "Link", ButtonData -> uri]

(* parse a leading markdown link to a guide URI; returns {{label, uri, rest}} or {} *)
guideLinkLeading[text_String] := StringCases[StringTrim[text],
    StartOfString ~~ "[" ~~ label : Shortest[Except["]"] ..] ~~ "](" ~~
        uri : Shortest[Except[")"] ..] ~~ ")" ~~ rest___ /;
        StringMatchQ[uri, "paclet:" ~~ ___ ~~ "guide/" ~~ ___] :> {label, uri, StringTrim[rest]}, 1]

(* a "## Functions" "### heading": a whole-heading guide link
   "### [Sub](paclet:.../guide/Sub)" becomes a ButtonBox(Link)
   GuideFunctionsSubsection that DocumentationBuild reads as a parent->child
   edge; a plain heading (or one with trailing prose) stays plain text. *)
guideSubsectionHead[text_String] := With[{m = guideLinkLeading[text]},
    If[m === {} || m[[1, 3]] =!= "",
        Cell[TextData @ inlineTextData[text], "GuideFunctionsSubsection"],
        Cell[BoxData[guideNavButtonBox[m[[1, 1]], m[[1, 2]]]], "GuideFunctionsSubsection"]
    ]
]

(* one "## Guides" index entry: a guide-link list item
   "- [Sub](paclet:.../guide/Sub) blurb" -> a GuideTOCLink cell carrying the
   ButtonBox(Link) (+ optional blurb). GuideTOCLink is a scanned cell style, so
   the edge registers; a non-guide-link item falls back to plain TOC text. *)
guideIndexCell[item_String] := With[{m = guideLinkLeading[item]},
    If[m === {},
        Cell[TextData @ inlineTextData[item], "GuideTOCLink"],
        With[{label = m[[1, 1]], uri = m[[1, 2]], desc = stripLeadingDash[m[[1, 3]]]},
            Cell[TextData @ If[desc === "",
                {Cell[BoxData[guideNavButtonBox[label, uri]], "InlineFormula"]},
                Join[{Cell[BoxData[guideNavButtonBox[label, uri]], "InlineFormula"], " \[LongDash] "}, inlineTextData[desc]]
            ], "GuideTOCLink"]
        ]
    ]
]

guideIndexCells[sections_, paclet_String] := If[paclet === "", {},
    Catenate @ Map[
        b |-> If[b["Type"] === "List", guideIndexCell /@ b["Items"], {}],
        Lookup[sections, "guides", {}]
    ]
]

(* walk the "## Functions" section in order so a Level-3 "###" heading becomes a
   GuideFunctionsSubsection divider above the function-link cells in its group
   instead of being dropped (issue #21).

   Each "###" subsection must HEAD its own CellGroupData group (heading cell +
   the function cells beneath it), matching the canonical guide shape. A flat
   GuideFunctionsSubsection cell sitting among sibling GuideText cells renders
   in the desktop FE but is SILENTLY DROPPED by DocumentationBuild - the built
   guide loses the subsection dividers entirely. Wrapping each subsection in its
   own group is what makes the build keep them.

   A bare Functions section with no "###" groups still produces one flat run of
   GuideText cells directly under the Functions section, same as before. *)
guideFunctionCells[sections_, paclet_String] := Block[{out = {}, cur = {}, head = None, blocks, flush},
    blocks = Lookup[sections, "functions", {}];
    If[ paclet === "", Return[{}] ];
    flush[] := If[head === None,
        out = Join[out, cur],
        AppendTo[out, Cell[CellGroupData[Prepend[cur, guideSubsectionHead[head]], Open]]]
    ];
    Do[
        Which[
            b["Type"] === "Heading" && b["Level"] === 3,
                flush[]; head = b["Text"]; cur = {},
            b["Type"] === "List",
                cur = Join[cur, Map[guideFunctionItem[#, paclet] &, b["Items"]]],
            (* a "---" between listing blocks is the palette's Delimiter - the
               thin rule that separates groups of related functions on a guide *)
            b["Type"] === "Separator",
                AppendTo[cur, Cell["\t", "GuideDelimiter"]]
        ],
        {b, blocks}
    ];
    flush[];
    out
]

guideNotebook[data_] := Block[{meta = data["meta"], sections = data["sections"], nb, title, abstract, paclet, fnCells, guideCells, sectionCells},
    nb = docTemplate["GuideBaseTemplateExt.nb"];
    (* the visible header is the human-readable Title (e.g. "Category Theory");
       fall back to Name ("CategoryTheory") only when no Title is given. *)
    title = Lookup[meta, "Title", Lookup[meta, "Name", ""]];
    paclet = Lookup[meta, "Paclet", ""];
    abstract = sectionText[sections, "abstract"];
    If[ abstract === "", abstract = Lookup[meta, "Description", ""] ];
    nb = fillDocString[nb, "GuideTitle", title];
    nb = fillDocString[nb, "GuideAbstract", abstract];
    (* the Functions section: replace the GuideText / InlineGuideFunctionListing
       placeholders with one GuideText chip-led cell per "## Functions" item.
       A "## Guides" section (a curated index of sub-guides) follows as its own
       "Guides" subsection of GuideTOCLink entries - those links build the
       documentation hierarchy / sidebar tree (see guideIndexCells). *)
    fnCells = guideFunctionCells[sections, paclet];
    guideCells = guideIndexCells[sections, paclet];
    sectionCells = Join[
        fnCells,
        If[ guideCells === {}, {},
            {Cell[CellGroupData[Prepend[guideCells, Cell["Guides", "GuideFunctionsSubsection"]], Open]]}
        ]
    ];
    If[ sectionCells =!= {},
        nb = nb /. Cell[CellGroupData[{sec : Cell[_, "GuideFunctionsSection", ___], ___}, st_], go___] :>
            Cell[CellGroupData[Prepend[sectionCells, sec], st], go]
    ];
    (* Related Guides are guide links *)
    With[{paclet = Lookup[meta, "Paclet", ""]},
        nb = fillDocCells[nb, "GuideMoreAbout", guideLinkContent[#, paclet, "guide"] & /@ asList @ Lookup[meta, "RelatedGuides", {}]]
    ];
    (* Tech Notes: the Guide template's GuideTutorial placeholders take one tutorial
       link per RelatedTutorials entry (mirrors GuideMoreAbout above). Without this the
       section header shipped empty and the XXXX placeholders were dropped below. *)
    With[{paclet = Lookup[meta, "Paclet", ""]},
        nb = fillDocCells[nb, "GuideTutorial", guideLinkContent[#, paclet, "tutorial"] & /@ asList @ Lookup[meta, "RelatedTutorials", {}]]
    ];
    (* Related Links are labeled hyperlinks; the template has only the section
       header (no placeholder), so insert one GuideRelatedLinks cell per link. *)
    With[{links = asList @ Lookup[meta, "Links", {}]},
        If[ links =!= {},
            nb = nb /. Cell[c_, "GuideRelatedLinksSection", o___] :>
                Sequence[Cell[c, "GuideRelatedLinksSection", o], Sequence @@ Map[Cell[linkItemContent[#], "GuideRelatedLinks"] &, links]]
        ]
    ];
    nb = fillDocList[nb, "Keywords", asList @ Lookup[meta, "Keywords", {}]];
    nb = nb /. {
        Cell["XXXX", _, ___] :> Nothing,
        Cell[BoxData["XXXX"], _, ___] :> Nothing,        Cell[c_, _, ___] /; ! FreeQ[c, FrameBox["XXXX"]] :> Nothing
    };
    setDocMetadata[fillCategorization[nb, "Guide", meta], meta, "Guide"]
]

(* === TechNote (tutorial) builder ===
   A tech note is free-flowing prose + code, not fixed sections. Fill the Title,
   replace the template's body placeholders with the converted markdown (headings
   -> Section/Subsection, prose -> Text, wl -> Input/Output, tables, lists), and
   keep + fill the Related Guides / Related Tech Notes / Categorization / Keywords. *)
$tutorialHeadingStyle = <|2 -> "Section", 3 -> "Subsection", 4 -> "Subsubsection"|>

tutorialBody[blocks_] := Block[{counter = 0},
    Catenate @ Map[
        block |-> Switch[block["Type"],
            "Heading", If[block["Level"] <= 1, {}, {Cell[headingText[block["Text"]], Lookup[$tutorialHeadingStyle, block["Level"], "Subsubsection"]]}],
            "Prose", {Cell[TextData @ inlineTextData[block["Text"]], "Text"]},
            "List", listItemCells[block, "Item"],
            "Table", {tableCell[block]},
            "Quote", {quoteCell[block["Text"]]},
            "MathBlock", {mathBlockCell[block["Text"]]},
            "Image", {imageCell[block]},
            "Code", If[executableQ[block], (counter += 1; exampleIOFor[block, counter]), withCellFlag[block, {nonExecutableCell[block]}]],
            _, {}
        ],
        blocks
    ]
]

tutorialNotebook[data_] := Block[{meta = data["meta"], nb, title, body, paclet, ma, rt},
    nb = docTemplate["TechNoteBaseTemplateExt.nb"];
    title = Lookup[meta, "Title", Lookup[meta, "Name", ""]];
    nb = fillDocString[nb, "Title", title];
    body = tutorialBody[data["blocks"]];
    (* rebuild the Title group: title cell + our body + the two link-section groups *)
    nb = nb /. Cell[CellGroupData[{tc : Cell[_, "Title", ___], ___,
            tma : Cell[CellGroupData[{Cell[_, "TutorialMoreAboutSection", ___], ___}, _], ___],
            rtg : Cell[CellGroupData[{Cell[_, "RelatedTutorialsSection", ___], ___}, _], ___]}, st_], go___] :>
        Cell[CellGroupData[Join[{tc}, body, {tma, rtg}], st], go];
    paclet = Lookup[meta, "Paclet", ""];
    ma = asList @ Lookup[meta, "RelatedGuides", {}];
    rt = asList @ Lookup[meta, "RelatedTutorials", {}];
    If[ ma =!= {} && paclet =!= "", nb = nb /. Cell[_, "TutorialMoreAbout", ___] :> linkRowCell[ma, "TutorialMoreAbout", paclet, "guide"] ];
    If[ rt =!= {} && paclet =!= "", nb = nb /. Cell[_, "RelatedTutorials", ___] :> linkRowCell[rt, "RelatedTutorials", paclet, "tutorial"] ];
    nb = fillDocList[nb, "Keywords", asList @ Lookup[meta, "Keywords", {}]];
    nb = nb /. {
        Cell["XXXX", _, ___] :> Nothing,
        Cell[BoxData["XXXX"], _, ___] :> Nothing,
        Cell[c_, _, ___] /; ! FreeQ[c, FrameBox["XXXX"]] :> Nothing
    };
    (* emit the modern "Tutorial" entity type, not the legacy "Tech Note" - DocumentationBuild
       renders it with the same TechNote page styling. CellContext stays CellGroup via the
       matching $docCellContextDefault entry, so cross-section state threading is unchanged. *)
    setDocMetadata[fillCategorization[nb, "Tutorial", meta], meta, "Tutorial"]
]

(* === Overview (paclet table-of-contents) builder ===
   An Overview page is the high-level table of contents the paclet's
   Documentation index links to; in the FE the Documentation Tools palette
   builds one with GenerateOverview by walking each tech-note's headings and
   wrapping them in TOC* cells (Title -> TOCChapter, Section -> TOCSection, ...).
   For markdown we map heading depth directly:

       # Title          -> TOCDocumentTitle (once, at the top)
       ## Chapter       -> TOCChapter
       ### Section      -> TOCSection
       #### Subsection  -> TOCSubsection
       ##### …          -> TOCSubsubsection

   Each heading text may carry a markdown link (`[label](paclet:…)` or the
   inferred `[Name]()` form) - when present, the TOC cell renders the heading
   as a clickable ButtonBox to that target, the same shape GenerateOverview
   emits. List items inherit a "one level deeper than the previous heading"
   so a chapter+bulleted-list entries pattern groups cleanly:

       ## Symbols       -> TOCChapter "Symbols"
       - [A]()          -> TOCSection link to A
       - [B]()          -> TOCSection link to B

   Categorization (Entity Type = "Overview") and the Paclet/Context/URI rows
   come from the frontmatter (Paclet/Context/URI keys), same convention the
   Symbol / Guide / TechNote builders use. *)
$tocStyleMap = <|
    1 -> "TOCDocumentTitle",
    2 -> "TOCChapter",
    3 -> "TOCSection",
    4 -> "TOCSubsection",
    5 -> "TOCSubsubsection",
    6 -> "TOCSubsubsubsection"
|>
tocStyleFor[level_Integer] := Lookup[$tocStyleMap, level, "TOCSubsubsubsection"]

(* parse a heading / list-item text into either an inline-formatted heading
   or a ButtonBox linked target - so "[Name](paclet:Pub/Pkg/tutorial/Name)"
   and the inferred "[Name]()" form both render as clickable TOC entries,
   and plain headings (or `code`-styled ones) carry their inline markup
   (backticks, bold, italic, math) the same way every other heading does. *)
tocCellContent[text_String, paclet_String] := Block[{trimmed = StringTrim[text], m},
    m = StringCases[trimmed, StartOfString ~~ "[" ~~ label : Shortest[Except["]"] ..] ~~ "](" ~~ url : Shortest[Except[")"] ...] ~~ ")" ~~ EndOfString :> {label, url}, 1];
    If[ m === {},
        headingText[trimmed],
        With[{label = m[[1, 1]], url = m[[1, 2]]},
            ButtonBox[label, BaseStyle -> "Link",
                ButtonData -> If[ url === "",
                    (* inferred link: assume a tutorial in the documented paclet,
                       since this is the conventional shape for an overview entry. *)
                    "paclet:" <> If[paclet === "", label, paclet <> "/tutorial/" <> label],
                    If[StringStartsQ[url, "paclet:" | "http"], url, "paclet:" <> url]
                ]
            ]
        ]
    ]
]

tocCell[content_, style_String] := Cell[
    Switch[Head[content],
        String, content,
        TextData, content,
        _, TextData[content]
    ],
    style
]

(* Walk the block stream once and build a nested CellGroupData tree of TOC*
   cells. A heading at depth N opens / continues a group at that depth, a list
   item under a heading at depth N becomes a leaf TOC cell at depth N+1.
   Everything else (prose, code, tables) is dropped - an overview is a TOC,
   not a body. A level-1 heading is silently dropped: the page title comes
   from the frontmatter "Name:" key and is filled into the template's
   single TOCDocumentTitle cell separately, so emitting another body cell
   of the same style would duplicate the title. *)
(* Fold threads the parent-heading depth through the block walk: each step
   sees the running depth and the cells emitted so far, and returns the
   updated pair. The result is a single allocation - no AppendTo growing a
   list one element at a time. *)
overviewBodyCells[blocks_, paclet_String] := Last @ Fold[
    Function[{state, block},
        Block[{depth = First[state], cells = Last[state], lvl},
            Switch[block["Type"],
                "Heading",
                    lvl = block["Level"];
                    If[ lvl >= 2,
                        {lvl, Append[cells, tocCell[tocCellContent[block["Text"], paclet], tocStyleFor[lvl]]]},
                        {depth, cells}
                    ],
                "List",
                    {depth, Join[cells, Map[
                        tocCell[tocCellContent[#, paclet], tocStyleFor[depth + 1]] &,
                        block["Items"]
                    ]]},
                _, state
            ]
        ]
    ],
    {1, {}},
    blocks
]

(* Group a flat sequence of TOC cells into the nested CellGroupData tree the
   front end uses for collapsible TOC sections. Each cell of style s opens a
   group, every following cell of a deeper style is a child of it, the first
   cell of equal-or-shallower depth closes the group. *)
$tocDepthOf = <|
    "TOCDocumentTitle" -> 0, "TOCChapter" -> 1, "TOCSection" -> 2,
    "TOCSubsection" -> 3, "TOCSubsubsection" -> 4, "TOCSubsubsubsection" -> 5
|>
groupTocCells[cells_List] := Block[{stack = {{}}, depths = {-1}, finalize},
    finalize[] := Block[{kids = First[stack], parentKids, headWithKids},
        stack = Rest[stack]; depths = Rest[depths];
        If[kids =!= {} && Length[stack] > 0,
            (* kids[[1]] is the head cell of this group; rest are its children *)
            headWithKids = If[Length[kids] >= 2,
                Cell[CellGroupData[kids, Open]],
                First[kids]
            ];
            parentKids = First[stack];
            stack = Prepend[Rest[stack], Append[parentKids, headWithKids]]
        ]
    ];
    Scan[
        cell |-> Block[{d = Lookup[$tocDepthOf, cell[[2]], 99]},
            While[Length[depths] > 1 && First[depths] >= d, finalize[]];
            stack = Prepend[stack, {cell}];
            depths = Prepend[depths, d];
        ],
        cells
    ];
    While[Length[stack] > 1, finalize[]];
    First[stack]
]

overviewNotebook[data_] := Block[{
    meta = data["meta"], blocks = data["blocks"],
    nb, title, paclet, tocCells, tocBlocks
},
    nb = docTemplate["OverviewBaseTemplateExt.nb"];
    title = Lookup[meta, "Name", Lookup[meta, "Title", ""]];
    paclet = Lookup[meta, "Paclet", ""];
    nb = nb /. Cell["XXXX", "TOCDocumentTitle", o___] :>
        Cell[If[title === "", "XXXX", title], "TOCDocumentTitle", o];
    tocCells = overviewBodyCells[blocks, paclet];
    tocBlocks = groupTocCells[tocCells];
    (* Force the title group's state to Open. The empty
       OverviewBaseTemplateExt.nb wraps its whole TOC in
       CellGroupData[..., Closed] (the author opens the title once and starts
       authoring), but a generated overview's body IS the content the reader
       is meant to see - leaving it Closed hides the entire TOC behind a
       click on the title. *)
    nb = nb /. Cell[CellGroupData[{titleCell : Cell[_, "TOCDocumentTitle", ___], _Cell | _ ..}, _], go___] :>
        Cell[CellGroupData[Prepend[tocBlocks, titleCell], Open], go];
    nb = fillDocList[nb, "Keywords", asList @ Lookup[meta, "Keywords", {}]];
    nb = nb /. {
        Cell["XXXX", _, ___] :> Nothing,
        Cell[BoxData["XXXX"], _, ___] :> Nothing
    };
    setDocMetadata[fillCategorization[nb, "Overview", meta], meta, "Overview"]
]

(* === default style-map builder ===
   No template/slots: markdown maps directly to standard documentation styles,
   so the author never writes cell styles. *)

$headingStyleMap = <|1 -> "Title", 2 -> "Section", 3 -> "Subsection", 4 -> "Subsubsection"|>

defaultNotebook[data_] := Block[{counter = 0, cells},
    cells = Catenate @ Map[
        block |-> applyBlockMeta[Switch[block["Type"],
            "Heading", {Cell[headingText[block["Text"]], Lookup[$headingStyleMap, block["Level"], "Subsubsection"]]},
            "Prose", {Cell[TextData @ inlineTextData[block["Text"]], "Text"]},
            "List", listItemCells[block, "Item"],
            "Table", {tableCell[block]},
            "Quote", {quoteCell[block["Text"]]},
            "MathBlock", {mathBlockCell[block["Text"]]},
            "Image", {imageCell[block]},
            "Code",
                If[ executableQ[block],
                    (counter += 1; exampleIOFor[block, counter]),
                    withCellFlag[block, {nonExecutableCell[block]}]
                ],
            _, {}
        ], block],
        data["blocks"]
    ];
    Notebook[cells, StyleDefinitions -> "Default.nb"]
]

(* === Computational Essay ===
   Stephen Wolfram's notebook genre: title, byline (author + date), an
   abstract paragraph, then narrative-driven body where every code cell sits
   between a short prose intro and its own one-line caption (the "CodeText"
   style cell). The published venue is the Notebook Archive / Wolfram
   Cloud, not a Function Repository submission, so the produced notebook
   is just a plain .nb with the Default stylesheet plus the essay's metadata
   header. Frontmatter beyond Name / Description carries Author, Date, and
   Abstract; the body falls through the same Heading / Prose / List / Code
   handlers the Default template uses, with code-block captions promoted to
   "CodeText" cells when they end in a colon. *)
essayHeaderCells[meta_] := Block[{title, author, date, abstract, cells = {}},
    title = Lookup[meta, "Name", Lookup[meta, "Title", ""]];
    author = Lookup[meta, "Author", Lookup[meta, "ContributedBy", ""]];
    date = Lookup[meta, "Date", ""];
    abstract = Lookup[meta, "Abstract", Lookup[meta, "Description", ""]];
    If[title =!= "", AppendTo[cells, Cell[title, "Title"]]];
    (* the official template's "Author" style takes one author cell; if a Date
       is given, append it after a bullet in the same cell. *)
    If[author =!= "" || date =!= "",
        AppendTo[cells, Cell[
            Which[
                author =!= "" && date =!= "", author <> " \[Bullet] " <> date,
                author =!= "", author,
                True, date
            ],
            "Author"
        ]]
    ];
    If[abstract =!= "",
        AppendTo[cells, Cell[TextData @ inlineTextData[abstract], "Abstract"]]
    ];
    cells
]

(* The official Computational Essay template - the same notebook
   File > New > Computational Essay opens, or that
   ResourceFunction["ComputationalEssayTemplate"][] returns - carries the
   essay's custom stylesheet (CodeText, Abstract, Author, ExampleDelimiter,
   the docked Notebook Analysis pod, etc.) and its TaggingRules. We use the
   template as the *shell* for the essay: cache the empty template once per
   session, then build our notebook with the template's StyleDefinitions
   so the body cells render in the right styles when opened in the FE.

   Pull any pending repository update first - the kernel routinely fires
   ResourceObject::updavb ("an update is available") when the locally
   cached resource is older than what's on the server, and that notice
   bypasses Quiet (it is printed via the resource-system print path, not
   the normal message system). ResourceUpdate refreshes the local cache so
   the subsequent call finds a current resource and the message is silent.
   Wrapped in Quiet/Check so a network failure here is benign - the older
   cached template still works. *)
$essayTemplate := $essayTemplate = Replace[
    Quiet @ UsingFrontEnd @ With[{nbo = (
        Quiet @ Check[ResourceUpdate["ComputationalEssayTemplate"], Null];
        ResourceFunction["ComputationalEssayTemplate"][]
    )},
        With[{nb = NotebookGet[nbo]}, NotebookClose[nbo]; nb]
    ],
    Except[_Notebook] -> Notebook[{}, StyleDefinitions -> "Default.nb"]
]

essayNotebook[data_] := Block[{meta = data["meta"], counter = 0, header, body,
    templateOpts = If[MatchQ[$essayTemplate, _Notebook], Rest[List @@ $essayTemplate],
        {StyleDefinitions -> "Default.nb"}]},
    header = essayHeaderCells[meta];
    body = Catenate @ MapIndexed[
        Function[{block, ix},
            Block[{type = block["Type"], text, captionStyle},
                Switch[type,
                    "Heading", {Cell[headingText[block["Text"]], Lookup[$headingStyleMap, block["Level"], "Subsubsection"]]},
                    "Prose", text = block["Text"];
                        (* a one-line prose paragraph that ends in ":" right before a
                           code cell is the essay's code-caption style ("CodeText");
                           ordinary multi-line / non-colon paragraphs stay "Text". *)
                        captionStyle = StringEndsQ[StringTrim[text], ":"] &&
                            ! StringContainsQ[text, "\n"] &&
                            ix[[1]] < Length[data["blocks"]] &&
                            Lookup[data["blocks"][[ix[[1]] + 1]], "Type", ""] === "Code";
                        {Cell[TextData @ inlineTextData[text], If[captionStyle, "CodeText", "Text"]]},
                    "List", listItemCells[block, "Item"],
                    "Table", {tableCell[block]},
                    "Quote", {quoteCell[block["Text"]]},
                    "MathBlock", {mathBlockCell[block["Text"]]},
                    "Image", {imageCell[block]},
                    "Code",
                        If[ executableQ[block],
                            counter += 1; exampleIOFor[block, counter],
                            withCellFlag[block, {nonExecutableCell[block]}]
                        ],
                    _, {}
                ]
            ]
        ],
        data["blocks"]
    ];
    Notebook[Join[header, body], Sequence @@ templateOpts]
]

(* === reference-subtype page builders ===
   The documentation system has reference page types beyond Symbol / Guide /
   TechNote: Format, ServiceConnection, Device, Interpreter, Entity, Character,
   Message, and Program pages (plus the Workflow / WorkflowGuide pages below).
   DocumentationTools ships no authoring template for any of them, so the
   authoring notebook is synthesized natively: the Categorization / Keywords
   metadata block, the type's title decoration, the body sections mapped from
   `## headings` to the type's section cell styles, the frontmatter link
   sections, and the examples group. The cell shapes mirror the corresponding
   DocuTools *BaseTemplate.nb authoring templates and the built pages shipped in
   the system documentation; every style referenced resolves in the shipped
   Reference.nb stylesheet, which the produced notebook uses as its
   StyleDefinitions. DocumentationBuild renames the generic content styles to
   the page-type forms at build time (Notes -> FormatNotes / ProgramNotes /
   ..., ObjectNameAlt -> ProgramName, ...), so the authored page carries the
   GENERIC styles plus the type-specific SECTION and title styles - the same
   split the DocuTools templates use. *)

$referenceStyleDefinitions = FrontEnd`FileName[{"Wolfram"}, "Reference.nb", CharacterEncoding -> "UTF-8"]

(* the Documentation/English subdirectory each doc template's built page ships
   in, for build scripts laying out a paclet (the URI kind is the matching
   PacletManager mapping: ReferencePages/Formats <-> ref/format, ... ). *)
$docTemplateDirectories = <|
    "Symbol" -> {"ReferencePages", "Symbols"},
    "Guide" -> {"Guides"},
    "TechNote" -> {"Tutorials"},
    "Overview" -> {"Tutorials"},
    "Format" -> {"ReferencePages", "Formats"},
    "ServiceConnection" -> {"ReferencePages", "Services"},
    "Device" -> {"ReferencePages", "Devices"},
    "Interpreter" -> {"ReferencePages", "Interpreters"},
    "Entity" -> {"ReferencePages", "Entities"},
    "Character" -> {"ReferencePages", "Characters"},
    "Message" -> {"ReferencePages", "Messages"},
    "Program" -> {"ReferencePages", "Programs"},
    "Workflow" -> {"Workflows"},
    "WorkflowGuide" -> {"WorkflowGuides"}
|>

(* the closed Categorization + Keywords groups every authoring template carries;
   the same CellLabel-keyed rows fillCategorization fills on the shipped
   templates, here synthesized directly from the frontmatter. *)
docMetaCells[entityType_String, meta_] := {
    Cell[CellGroupData[Join[
        {Cell["Categorization", "CategorizationSection"],
         Cell[entityType, "Categorization", CellLabel -> "Entity Type"]},
        If[Lookup[meta, "Paclet", ""] =!= "", {Cell[meta["Paclet"], "Categorization", CellLabel -> "Paclet Name"]}, {}],
        If[Lookup[meta, "Context", ""] =!= "", {Cell[meta["Context"], "Categorization", CellLabel -> "Context"]}, {}],
        If[Lookup[meta, "URI", ""] =!= "", {Cell[meta["URI"], "Categorization", CellLabel -> "URI"]}, {}]
    ], Closed]],
    With[{kw = asList @ Lookup[meta, "Keywords", {}]},
        If[kw === {}, Nothing,
            Cell[CellGroupData[Join[
                {Cell["Keywords", "KeywordsSection"]},
                Map[Cell[#, "Keywords"] &, kw]
            ], Closed]]
        ]
    ]
}

(* a quoted title: the name wrapped in literal straight quotes (each its own
   InterpreterTitleQuotes inline cell) followed by a parenthesized subtitle -
   the shape ServiceConnection / Device / Interpreter pages use. *)
quotedTitleCell[name_String, subtitle_String, subtitleStyle_String] := Cell[TextData[{
    Cell["\"", "InterpreterTitleQuotes"], name, Cell["\"", "InterpreterTitleQuotes"],
    " ", Cell["(" <> subtitle <> ")", subtitleStyle]
}], "ObjectNameAlt"]

(* per-type title cells. Device keeps the DocuTools template's separate
   DeviceSubtitle cell; Format appends the gray FilenameExtension when the
   frontmatter carries `Extension: .xyz`; Character emits the glyph grid
   (TraditionalForm / StandardForm at 72pt) over a raw-string CharacterName -
   DocumentationBuild extracts the title with a _String pattern, so the name
   cell must NOT be TextData-wrapped. *)
refTitleCells["Format", meta_, name_] := With[{ext = Lookup[meta, "Extension", ""]},
    {If[ext === "",
        Cell[name, "ObjectNameAlt"],
        Cell[TextData[{name <> " ", StyleBox["(" <> ext <> ")", "FilenameExtension"]}], "ObjectNameAlt"]]}
]
refTitleCells["ServiceConnection", meta_, name_] := {quotedTitleCell[name, "Service Connection", "ServiceSubtitle"]}
(* the device subtitle rides INSIDE the title cell (the shape the built pages
   use), so the ObjectNameAlt cell stays the single head of the title group *)
refTitleCells["Device", meta_, name_] := {Cell[
    TextData[Join[
        {Cell["\"", "InterpreterTitleQuotes"], name, Cell["\"", "InterpreterTitleQuotes"], " "},
        With[{sub = Lookup[meta, "Subtitle", ""]},
            If[sub === "", {}, {Cell["(" <> sub <> ")", "DeviceSubtitle"]}]]
    ]], "ObjectNameAlt"]}
refTitleCells["Interpreter", meta_, name_] := {quotedTitleCell[name, "Interpreter Type", "InterpreterSubtitle"]}
refTitleCells["Entity", meta_, name_] := {Cell[name, "ObjectNameAlt"]}
refTitleCells["Character", meta_, name_] := With[{ch = Lookup[meta, "Character", name]},
    {Cell[BoxData[GridBox[{{StyleBox[ch, "TradFormChar"], StyleBox[ch, "StandFormChar"]}},
         GridBoxAlignment -> {"Columns" -> {{Center}}}]], "CharacterImage"],
     Cell[ch, "CharacterName"]}
]
refTitleCells["Message", meta_, name_] := {Cell[name, "ObjectName"]}
refTitleCells["Program", meta_, name_] := {Cell[name, "ObjectNameAlt"]}
refTitleCells[_, meta_, name_] := {Cell[name, "ObjectNameAlt"]}

(* markdown `## heading` -> the type's section cell style; keys are
   sectionKey-normalized. A heading not in the map takes the type's default
   (custom sections are normal on these pages - a Program page's extra
   ALL-CAPS sections, a service's request groups). *)
$refSubtypeConfig = <|
    "Format" -> <|
        "EntityType" -> "Format",
        "AbstractStyle" -> "Usage",
        "DefaultSectionStyle" -> "ImportExportSection",
        "SectionStyles" -> <|
            "background and context" -> "FormatBackground",
            "import and export" -> "ImportExportSection",
            "notebook interface" -> "NotebookInterfaceSection",
            "import elements" -> "ElementsSection",
            "export elements" -> "ExportElementsSection",
            "options" -> "OptionsSection",
            "import options" -> "ImportOptionsSection",
            "export options" -> "ExportOptionsSection"|>
    |>,
    "ServiceConnection" -> <|
        "EntityType" -> "Service Connection",
        "AbstractStyle" -> "ServiceAbstract",
        "DefaultSectionStyle" -> "ServiceSubsection",
        "SectionStyles" -> <||>,
        "SubsectionStyle" -> "GuideFunctionsSubsection"
    |>,
    "Device" -> <|
        "EntityType" -> "Device Connection",
        "AbstractStyle" -> "DeviceAbstract",
        "DefaultSectionStyle" -> "DeviceSubsection",
        "SectionStyles" -> <||>
    |>,
    "Interpreter" -> <|
        "EntityType" -> "Interpreter",
        "AbstractStyle" -> "Usage",
        "DefaultSectionStyle" -> "InterpreterSection",
        "SectionStyles" -> <||>,
        "ExtraLinkSections" -> {{"RelatedInterpreters", "RelatedInterpreterSection", "Related Interpreters", "RelatedInterpreters", "ref/interpreter"}}
    |>,
    "Entity" -> <|
        "EntityType" -> "Entity",
        "AbstractStyle" -> "Usage",
        "DefaultSectionStyle" -> "EntitySection",
        "SectionStyles" -> <||>,
        "ExtraLinkSections" -> {
            {"RelatedEntities", "RelatedEntitySection", "Related Entity Types", "RelatedEntities", "ref/entity"},
            {"RelatedInterpreters", "RelatedInterpreterSection", "Related Interpreters", "RelatedInterpreters", "ref/interpreter"}}
    |>,
    "Character" -> <|
        "EntityType" -> "Character Name",
        "AbstractStyle" -> "Notes",
        "DefaultSectionStyle" -> "Section",
        "SectionStyles" -> <||>
    |>,
    "Message" -> <|
        "EntityType" -> "Message",
        "AbstractStyle" -> "Notes",
        "DefaultSectionStyle" -> "Section",
        "SectionStyles" -> <||>
    |>,
    "Program" -> <|
        "EntityType" -> "Program",
        "AbstractStyle" -> "Usage",
        "DefaultSectionStyle" -> "ProgramSection",
        "SectionStyles" -> <||>,
        "SubsectionStyle" -> "ProgramSubsection"
    |>
|>

(* the frontmatter link sections every subtype page understands; each entry is
   {frontmatter key, section cell style, section title, item cell style, link
   kind}. kind None marks external links ([label](url) markdown, rendered by
   inlineTextData as hyperlink ButtonBoxes). *)
$refCommonLinkSections = {
    {"SeeAlso", "SeeAlsoSection", "See Also", "SeeAlso", "ref"},
    {"RelatedTutorials", "TutorialsSection", "Tech Notes", "Tutorials", "tutorial"},
    {"RelatedWorkflows", "RelatedWorkflowsSection", "Related Workflows", "RelatedWorkflows", "workflow"},
    {"RelatedGuides", "MoreAboutSection", "Related Guides", "MoreAbout", "guide"},
    {"Links", "RelatedLinksSection", "Related Links", "RelatedLinks", None}
}

refLinkSectionCells[meta_, linkSections_] := Block[{paclet = Lookup[meta, "Paclet", ""]},
    Catenate @ Map[
        Function[{spec},
            With[{names = asList @ Lookup[meta, spec[[1]], {}]},
                If[ names === {}, {},
                    {Cell[CellGroupData[Join[
                        {Cell[spec[[3]], spec[[2]]]},
                        If[ spec[[5]] === None,
                            Map[Cell[TextData @ inlineTextData[#], spec[[4]]] &, names],
                            {linkRowCell[names, spec[[4]], paclet, spec[[5]]]}
                        ]
                    ], Open]]}
                ]
            ]
        ],
        linkSections
    ]
]

(* body-section content: prose / lists / tables as Notes-context cells (the
   authored form the DocuTools templates use; DocumentationBuild renames them
   to the type's *Notes styles), a `---` rule as the WeakDivider that separates
   an import group from an export group, and code as evaluated Input / Output
   pairs. $refCounter is dynamically scoped from the page builder's Block so
   In / Out numbering runs through all body sections. A Program page's
   `- <code>form</code> -- text` bullets split into the ProgramCodeText +
   ProgramNameNotes pair of the man-page layout; its foreign-language fences
   become ProgramInput cells. *)
programPairCells[item_String] := With[{
    m = StringCases[item, StartOfString ~~ "`" ~~ c__ ~~ "`" ~~ Whitespace ~~ "--" ~~ Whitespace ~~ d__ ~~ EndOfString :> {c, d}]
},
    If[ m === {},
        {Cell[TextData @ inlineTextData[item], "Notes"]},
        {Cell[m[[1, 1]], "ProgramCodeText"],
         Cell[TextData @ inlineTextData[m[[1, 2]]], "ProgramNameNotes"]}
    ]
]

refSectionContent[type_String, blocks_, subsectionStyle_String] := Catenate @ Map[
    Function[{block},
        Switch[block["Type"],
            "Heading",
                {Cell[headingText[block["Text"]], subsectionStyle]},
            "Prose",
                applyBlockMeta[{Cell[TextData @ inlineTextData[block["Text"]], "Notes"]}, block],
            "List",
                applyBlockMeta[
                    If[ type === "Program",
                        Catenate @ Map[programPairCells, block["Items"]],
                        listItemCells[block, "Notes"]
                    ], block],
            "Table",
                applyBlockMeta[{tableCell[block]}, block],
            "Quote",
                applyBlockMeta[{quoteCell[block["Text"]]}, block],
            "MathBlock",
                applyBlockMeta[{mathBlockCell[block["Text"]]}, block],
            "Image",
                applyBlockMeta[{imageCell[block]}, block],
            "Separator",
                {Cell["", "WeakDivider"]},
            "Code",
                If[ executableQ[block],
                    $refCounter++; applyBlockMeta[exampleIOFor[block, $refCounter], block],
                    applyBlockMeta[withCellFlag[block,
                        {If[ type === "Program" && ! MemberQ[{"wl", "wolfram", "mathematica"}, block["Lang"]],
                            Cell[block["Code"], "ProgramInput"],
                            nonExecutableCell[block]]}], block]
                ],
            _, {}
        ]
    ],
    blocks
]

(* split the block stream into ordered {heading | None, blocks} section chunks:
   Split starts a new run at every level-2 heading, the H1 (the page title -
   the frontmatter Name renders it) is dropped, and content before the first H2
   is the intro chunk. *)
refSectionChunks[blocks_] := Map[
    If[ #[[1]]["Type"] === "Heading" && #[[1]]["Level"] === 2,
        {#[[1]], Rest[#]},
        {None, #}
    ] &,
    Split[
        DeleteCases[blocks, b_ /; b["Type"] === "Heading" && b["Level"] === 1],
        ! (#2["Type"] === "Heading" && #2["Level"] === 2) &
    ]
]

(* The abstract-flavored section titles: their content lands in the type's
   abstract style directly under the title instead of opening a body section.
   "Background & Context" belongs here for a Format page: on a built page that
   heading is the USAGE block (DocumentationBuild wraps the usage cells in its
   own FormatBackground section), so authoring it as a section too produced a
   duplicate the build relocated to the bottom of the page. *)
$refAbstractKeys = {"abstract", "usage", "basic description", "description", "background and context"}

(* the section titles that open the examples group; "basic examples" is the
   form a NotebookToMarkdown twin emits for the PrimaryExamplesSection cell,
   so accepting it keeps the round-trip a fixpoint. *)
$refExamplesKeys = {"examples", "basic examples", "more examples"}

(* Nest a flat cell run into the CellGroupData tree DocumentationBuild needs.
   levelOf gives each cell its outline level (1 = section, 2 = subsection, ...;
   Infinity = ordinary content); a cell of level n opens a group that swallows
   every following cell of deeper level. Without this nesting the build cannot
   tell where one section ends: flat body cells are swept into whichever
   section group follows them (they vanished into See Also), the same failure
   groupPrimaryExamples fixes for the examples section. *)
nestCells[{}, _] := {}
nestCells[cells_List, levelOf_] := Block[{first = First[cells], lvl, children},
    lvl = levelOf[first];
    If[ lvl === Infinity,
        Prepend[nestCells[Rest[cells], levelOf], first],
        children = TakeWhile[Rest[cells], levelOf[#] > lvl &];
        Prepend[
            nestCells[Drop[cells, 1 + Length[children]], levelOf],
            Cell[CellGroupData[Prepend[nestCells[children, levelOf], first], Open]]
        ]
    ]
]

(* the outline level of a cell, given the styles that open a level *)
styleLevelFunction[levels_List] := Function[cell,
    Replace[cell, {
        Cell[_, s_String, ___] :> Replace[FirstPosition[levels, l_List /; MemberQ[l, s], None, {1}],
            {{i_Integer} :> i, _ -> Infinity}],
        _ -> Infinity
    }]
]

(* one chunk -> its cells, tagged by role so the assembly can order
   abstract / body / examples without growing lists imperatively *)
refChunkCells[type_String, cfg_, subStyle_String, {heading_, blocks_}] := Block[{
    key = If[heading === None, "", sectionKey[heading["Text"]]]
},
    Which[
        heading === None || MemberQ[$refAbstractKeys, key],
            "abstract" -> Catenate @ Map[
                Function[{b}, Switch[b["Type"],
                    "Prose", applyBlockMeta[{Cell[TextData @ inlineTextData[b["Text"]], cfg["AbstractStyle"]]}, b],
                    (* abstract bullets stay in the abstract style (a Format
                       page's Background & Context bullets are usage lines) *)
                    "List", listItemCells[b, cfg["AbstractStyle"]],
                    _, refSectionContent[type, {b}, subStyle]
                ]],
                blocks],
        MemberQ[$refExamplesKeys, key],
            (* A "### Basic Examples" heading inside the examples section is
               dropped: DocumentationBuild already wraps the primary examples in
               its own "Basic Examples" ExampleSection, so keeping ours rendered
               the title twice (Examples > Basic Examples > Basic Examples).
               Any other subsection heading is a real extra example section. *)
            "examples" -> {Cell[CellGroupData[Join[
                {Cell["Examples", "PrimaryExamplesSection", CellTags -> "PrimaryExamplesSection"]},
                exampleContent[
                    DeleteCases[blocks,
                        b_ /; b["Type"] === "Heading" && sectionKey[b["Text"]] === "basic examples"],
                    "ExampleText"]
            ], Open]]},
        True,
            "body" -> Join[
                {Cell[headingText[heading["Text"]], Lookup[cfg["SectionStyles"], key, cfg["DefaultSectionStyle"]]]},
                refSectionContent[type, blocks, subStyle]
            ]
    ]
]

refSubtypeNotebook[type_String, data_] := Block[{
    meta = data["meta"], cfg = $refSubtypeConfig[type], name, subStyle,
    tagged, sectionStyles, $refCounter = 0
},
    name = Lookup[meta, "Name", Lookup[meta, "Title", ""]];
    subStyle = Lookup[cfg, "SubsectionStyle", "Subsection"];
    tagged = Map[refChunkCells[type, cfg, subStyle, #] &, refSectionChunks[data["blocks"]]];
    sectionStyles = Append[Values[cfg["SectionStyles"]], cfg["DefaultSectionStyle"]];
    setDocMetadata[
        Notebook[Join[
            docMetaCells[cfg["EntityType"], meta],
            (* the title cell heads a group holding the abstract - the shape the
               authoring templates use (GROUP ObjectNameAlt > ServiceAbstract;
               a Character page's CharacterImage heads and CharacterName sits
               inside it) *)
            {Cell[CellGroupData[Join[
                refTitleCells[type, meta, name],
                Catenate @ Cases[tagged, ("abstract" -> cells_) :> cells]
            ], Open]]},
            (* each body section is its own group, subsections nested inside *)
            nestCells[
                Catenate @ Cases[tagged, ("body" -> cells_) :> cells],
                styleLevelFunction[{sectionStyles, {subStyle}}]],
            Catenate @ Cases[tagged, ("examples" -> cells_) :> cells],
            refLinkSectionCells[meta, Join[$refCommonLinkSections, Lookup[cfg, "ExtraLinkSections", {}]]]
        ], StyleDefinitions -> $referenceStyleDefinitions, LightDark -> "Light"],
        meta, cfg["EntityType"]
    ]
]

(* === Workflow / WorkflowGuide page builders ===
   A Workflow page is a numbered step-by-step procedure: the WorkflowStep style
   renders its own circled counter (reset by every WorkflowHeader), so steps
   are authored as plain `### heading` cells with NO literal numbers. Markdown
   mapping: `## X` -> WorkflowHeader (a step-group header, which restarts the
   counter), `### X` -> WorkflowStep, prose -> WorkflowText, `> note` ->
   WorkflowParenthetical, `---` -> WorkflowDelimiter, code -> evaluated
   Input / Output. The footer link sections use the authoring styles (SeeAlso
   here means related WORKFLOWS; RelatedFunctions carries the symbol links).

   No markdown maps to WorkflowPlatform: the Desktop / Cloud / Mobile platform
   tabs are a multi-platform authoring device whose cell is a platform ICON
   (a GraphicsBox) plus StyleBox[name, "WorkflowPlatform"], which the build's
   workflow finisher rewrites into a Dynamic CellOpen keyed to the notebook's
   "SelectedPlatform" tagging rule. A plain text cell in that style is not
   recognized and the finisher drops the whole platform group - so a
   single-platform page simply does not open one. *)

(* every prose block before the first level-2 heading, joined - a workflow
   page's lead paragraphs ARE its description. They MUST all move into the
   WorkflowDescription cell: DocumentationBuild's workflow assembly stops at
   the first cell it does not expect between the description and the opening
   platform / step group, silently dropping the rest of the page. *)
leadingProse[blocks_] := StringRiffle[
    Cases[
        TakeWhile[blocks, ! (#["Type"] === "Heading" && #["Level"] === 2) &],
        b_ /; b["Type"] === "Prose" :> b["Text"]],
    " "]

workflowNotebook[data_] := Block[{meta = data["meta"], name, lead, desc, bodyBlocks, body, counter = 0},
    name = Lookup[meta, "Title", Lookup[meta, "Name", ""]];
    (* the visible blurb is the lead prose when the page has any (the
       frontmatter Description still carries the metadata summary); a page with
       no lead paragraph falls back to that Description. Either way no prose is
       left stranded ahead of the first step group. *)
    lead = leadingProse[data["blocks"]];
    desc = If[lead === "", Lookup[meta, "Description", ""], lead];
    (* drop the prose from the LEADING run only (everything before the first
       level-2 heading); prose further down belongs to its step *)
    bodyBlocks = With[{
        split = TakeDrop[data["blocks"],
            LengthWhile[data["blocks"], ! (#["Type"] === "Heading" && #["Level"] === 2) &]]
    },
        Join[DeleteCases[First[split], b_ /; b["Type"] === "Prose"], Last[split]]
    ];
    body = Catenate @ Map[
        Function[{b},
            Switch[b["Type"],
                "Heading",
                    Which[
                        b["Level"] <= 1, {},
                        b["Level"] === 2, {Cell[headingText[b["Text"]], "WorkflowHeader"]},
                        True, {Cell[headingText[b["Text"]], "WorkflowStep"]}
                    ],
                "Prose", applyBlockMeta[{Cell[TextData @ inlineTextData[b["Text"]], "WorkflowText"]}, b],
                "List", applyBlockMeta[listItemCells[b, "WorkflowText"], b],
                "Quote", applyBlockMeta[{Cell[TextData @ inlineTextData[b["Text"]], "WorkflowParenthetical"]}, b],
                "Separator", {Cell["", "WorkflowDelimiter"]},
                "Table", applyBlockMeta[{tableCell[b]}, b],
                "MathBlock", applyBlockMeta[{mathBlockCell[b["Text"]]}, b],
                "Image", applyBlockMeta[{imageCell[b]}, b],
                "Code",
                    If[ executableQ[b],
                        counter++; applyBlockMeta[exampleIOFor[b, counter], b],
                        applyBlockMeta[withCellFlag[b, {nonExecutableCell[b]}], b]
                    ],
                _, {}
            ]
        ],
        bodyBlocks
    ];
    (* a workflow page nests EVERYTHING under its title group: the description,
       the platform / step-header / step groups (step counters reset per group),
       and the footer link sections *)
    setDocMetadata[
        Notebook[Join[
            docMetaCells["Workflow", meta],
            {Cell[CellGroupData[Join[
                {Cell[name, "WorkflowTitle"]},
                If[desc === "", {}, {Cell[TextData @ inlineTextData[desc], "WorkflowDescription"]}],
                nestCells[body, styleLevelFunction[{{"WorkflowHeader"}, {"WorkflowStep"}}]],
                refLinkSectionCells[meta, {
                    {"SeeAlso", "SeeAlsoSection", "See Also", "SeeAlso", "workflow"},
                    {"RelatedFunctions", "RelatedFunctionsSection", "Related Functions", "RelatedFunctions", "ref"},
                    {"RelatedGuides", "RelatedGuidesSection", "Related Guides", "RelatedGuides", "guide"},
                    {"RelatedTutorials", "TechNotesSection", "Tech Notes", "TechNotes", "tutorial"},
                    {"Links", "RelatedLinksSection", "Related Links", "RelatedLinks", None}
                }]
            ], Open]]}
        ], StyleDefinitions -> $referenceStyleDefinitions, LightDark -> "Light"],
        meta, "Workflow"
    ]
]

(* A WorkflowGuide is a curated index of workflow pages: `## X` ->
   WorkflowGuideSection, each `- [label](target)` bullet -> a WorkflowGuideEntry
   link, `---` -> WorkflowGuideDelimiter, prose -> WorkflowGuideText. An empty
   target infers the workflow kind (paclet:<paclet>/workflow/<label>, spaces
   dropped from the page name); an explicit target is used verbatim, gaining
   the paclet: scheme when it is a bare URI. A plain-text bullet stays a plain
   entry. *)
workflowGuideEntryCell[item_String, paclet_String] := Block[{
    m = StringCases[StringTrim[item],
        StartOfString ~~ "[" ~~ label : Shortest[Except["]"] ..] ~~ "](" ~~ url : Shortest[Except[")"] ...] ~~ ")" ~~ EndOfString :> {label, url}, 1]
},
    If[ m === {},
        Cell[TextData @ inlineTextData[item], "WorkflowGuideEntry"],
        With[{label = m[[1, 1]], url = m[[1, 2]]},
            Cell[TextData[{ButtonBox[label, BaseStyle -> "Link",
                ButtonData -> Which[
                    url === "",
                        "paclet:" <> If[paclet === "", "", paclet <> "/"] <> "workflow/" <> StringReplace[label, " " -> ""],
                    StringStartsQ[url, "paclet:" | "http"],
                        url,
                    True,
                        "paclet:" <> url
                ]]}], "WorkflowGuideEntry"]
        ]
    ]
]

workflowGuideNotebook[data_] := Block[{meta = data["meta"], name, paclet, body},
    name = Lookup[meta, "Title", Lookup[meta, "Name", ""]];
    paclet = Lookup[meta, "Paclet", ""];
    body = Catenate @ Map[
        Function[{b},
            Switch[b["Type"],
                "Heading", If[b["Level"] <= 1, {}, {Cell[headingText[b["Text"]], "WorkflowGuideSection"]}],
                "Prose", applyBlockMeta[{Cell[TextData @ inlineTextData[b["Text"]], "WorkflowGuideText"]}, b],
                "List", applyBlockMeta[Map[workflowGuideEntryCell[#, paclet] &, b["Items"]], b],
                "Separator", {Cell["", "WorkflowGuideDelimiter"]},
                _, {}
            ]
        ],
        data["blocks"]
    ];
    (* like a workflow page, everything nests under the title group *)
    setDocMetadata[
        Notebook[Join[
            docMetaCells["Workflow Guide", meta],
            {Cell[CellGroupData[Join[
                {Cell[name, "WorkflowGuideTitle"]},
                nestCells[body, styleLevelFunction[{{"WorkflowGuideSection"}}]],
                refLinkSectionCells[meta, {
                    {"RelatedWorkflowGuides", "WorkflowGuideRelatedWorkflowGuidesSection", "Related Workflow Guides", "WorkflowGuideRelatedWorkflowGuide", "workflowguide"},
                    {"RelatedGuides", "WorkflowGuideRelatedGuidesSection", "Related Guides", "WorkflowGuideRelatedGuide", "guide"},
                    {"Links", "WorkflowGuideRelatedLinksSection", "Related Links", "WorkflowGuideRelatedLink", None}
                }]
            ], Open]]}
        ], StyleDefinitions -> $referenceStyleDefinitions, LightDark -> "Light"],
        meta, "Workflow Guide"
    ]
]

(* === template registry === *)

(* the Paclet template also wraps its directory / main-guide / context metadata
   in TemplateExpression / TemplateIf (not plain TemplateSlot). Those resolve to
   raw values (strings, Missing, or boxes), not cells, so they are evaluated in a
   first pass; CheckDefinitionNotebook flags any left unresolved. *)
rawSlotValue[name_String, opts_List, meta_] := Block[{def = FirstCase[opts, (DefaultValue -> v_) :> v, Missing[]]},
    Switch[name,
        "PacletDirectoryType", If[MissingQ[def], "Notebook", def],
        "Context", Lookup[meta, "Context", If[MissingQ[def], "MyPublisherID`MyPaclet`", def]],
        "MainGuidePageString", Lookup[meta, "MainGuide", def],
        (* The Paclet template's license control is a radio group with five
           known IDs ("MIT", "Apache-2.0", "CC0-1.0", "None", "Other") plus a
           free-text input that activates when "Other" is the selected radio.
           Frontmatter License: <something> can be any of:
           - a known-radio ID (MIT / Apache-2.0 / CC0-1.0 / None / Other)
             -> SelectedLicenseID picks that radio, SpecifiedLicenseID stays
             at the template's default;
           - any other string (e.g. "GPL-3.0-or-later", "BSD-3-Clause", a
             custom phrasing) -> SelectedLicenseID points at the "Other"
             radio and SpecifiedLicenseID carries the verbatim string, so
             the free-text input fills correctly in the FE.
           Without the second branch a non-radio License silently vanishes:
           SelectedLicenseID gets a string no radio matches (none lights up)
           and SpecifiedLicenseID is left at its default Null. *)
        "SelectedLicenseID", If[
            KeyExistsQ[meta, "License"],
            If[ MatchQ[meta["License"], "MIT" | "Apache-2.0" | "CC0-1.0" | "None" | "Other"],
                meta["License"],
                "Other"
            ],
            def
        ],
        "SpecifiedLicenseID", Block[{lic = Lookup[meta, "License", Missing[]]},
            If[ StringQ[lic] && ! MatchQ[lic, "MIT" | "Apache-2.0" | "CC0-1.0" | "None" | "Other"],
                lic,
                def
            ]
        ],
        _, Lookup[meta, name, def]
    ]
]

(* Resolve in stages: slots must be substituted before the enclosing TemplateIf
   collapses, otherwise its condition (e.g. StringQ[TemplateSlot[...]]) is tested
   on the inert slot and always fails; TemplateExpression is unwrapped last so its
   body (DeleteMissing/ToBoxes/...) then evaluates normally. *)
resolveTemplateExpressions[template_, meta_] := template /. te : (_TemplateExpression | _TemplateIf) :> Block[{t = te},
    t = t //. TemplateSlot[n_String, o___] :> rawSlotValue[n, {o}, meta];
    t = t //. {TemplateIf[cond_, a_] :> If[TrueQ[cond], a, Missing[]], TemplateIf[cond_, a_, b_] :> If[TrueQ[cond], a, b]};
    t //. TemplateExpression[e_, ___] :> e
]

(* resource definition notebooks (Function Repository, Paclet Repository): fill
   the official template's slots and keep everything else (stylesheet + docked
   Deploy/Submit toolbar) intact, so the .nb is publishable as-is. *)
(* Paclet template's nine canonical disclosure checkboxes.  Each appears in
   the produced notebook as a standalone CheckboxBox[False, {False, name}]
   whose `name` is one of these tags; ticking it switches the current value
   from False to the tag string ({False, tag} is the {off, on} pair).  The
   resource system's CheckboxesCell autofails on Property -> "Disclosures",
   so unlike Categories / CompatibilityFeatures these are filled by
   walking the template and flipping the matching boxes individually.
   Authors set them via a frontmatter list: Disclosures: [LocalFiles,
   ExternalServices].  Unknown names are silently ignored. *)
$pacletDisclosureNames = {
    "LocalFiles", "ExternalServices", "LocalSystemInteractions",
    "OSConfiguration", "PacletDependencies", "WLSystemConfiguration",
    "WLSystemSymbols", "WolframAccount", "Other"
}

applyPacletDisclosures[nb_, meta_Association] := With[{
    want = Intersection[
        asList @ Lookup[meta, "Disclosures", {}],
        $pacletDisclosureNames
    ]
},
    If[ want === {},
        nb,
        nb /. Verbatim[CheckboxBox][False, {False, tag_String}] /; MemberQ[want, tag] :>
            CheckboxBox[tag, {False, tag}]
    ]
]
applyPacletDisclosures[other_, _] := other


resourceNotebook[resourceType_String, data0_] := Block[{template, data = Append[data0, "resourceType" -> resourceType]},
    Needs["DefinitionNotebookClient`"];
    template = DefinitionNotebookClient`DefinitionTemplate[resourceType];
    template = resolveTemplateExpressions[template, data["meta"]];
    (* scalar slots that live in held TaggingRules (a license radio value, a guide
       path) must be replaced by their raw value directly - the cell-fill pass
       below wraps results in Sequence@@, which would leave a stray Sequence[...]
       in the held option and break the control. *)
    template = template /. TemplateSlot[n : ("SelectedLicenseID" | "SpecifiedLicenseID" | "MainGuidePageString"), o___] :>
        rawSlotValue[n, {o}, data["meta"]];
    (* ReplaceRepeated: some slots (e.g. the Compatibility group) nest sub-slots
       inside their DefaultValue, which a single pass would not reach. *)
    template = template //. TemplateSlot[n_, o___] :> Sequence @@ fillSlot[n, {o}, data];
    (* "Disclosures: [list]" frontmatter toggles the named Paclet disclosure
       checkboxes (see applyPacletDisclosures); a no-op for templates whose
       Disclosures section has no such checkboxes, or for documents that
       omit the frontmatter key. *)
    template = applyPacletDisclosures[template, data["meta"]];
    (* the template seeds a blank standalone usage-input placeholder beside the
       Usage slot (for a second usage line); we fill all usage from the markdown,
       so drop any UsageInputs cell with no real content (matched by emptiness,
       not a literal BoxData[] - the template's BoxData is a context-shadowed
       symbol the bare pattern misses) rather than leave a blank usage line. *)
    template = template /. c : Cell[_, "UsageInputs", ___] /;
        StringTrim[StringJoin[Cases[First[c], _String, Infinity]]] === "" :> Nothing;
    (* collapse the Definition section by default - the inlined source can be long.
       The section header is a "Section" cell tagged "Definition". *)
    template = template /. Cell[CellGroupData[{hdr : Cell[_, "Section", ___, CellTags -> {___, "Definition", ___}, ___], body___}, Open], go___] :>
        Cell[CellGroupData[{hdr, body}, Closed], go];
    (* pin the deployed notebook to light mode so the cloud page never renders
       dark (LightDark -> "Light" forces light regardless of the viewer theme). *)
    Replace[template, Notebook[cells_, o___] :>
        Notebook[cells, LightDark -> "Light", Sequence @@ FilterRules[{o}, Except[LightDark]]]]
]

(* === Template: Chapter (Wolfram Book Tools) ===
   A chapter notebook in the WolframBookTools sense: one Section heading
   (with CounterAssignments -> {{"Section", n-1}, ...}), then body blocks
   in the BookToolsStyles vocabulary. The H1 of the markdown is the chapter
   title; the frontmatter "ChapterNumber:" sets the counter. H2 headings
   are Subsection by default, but a fixed set of reserved titles
   (Summary / Vocabulary / Exercises / Q&A / Tech Notes / More to Explore
   / References / Takeaways / Resources / Key Concepts) drop the block
   that follows them into the matching book-style back-matter section
   instead. Multi-cell scaffolds that have no direct markdown analogue
   (SolvedExample, Theorem/Proof, Exercise/Solution) are authored as
   Pandoc-style ":::" fenced divs - see docs/book-palette.md for the full
   markdown <-> cell-style mapping. *)

$bookStyleSheet := FrontEnd`FileName[{"Wolfram"}, "BookToolsStyles.nb",
    CharacterEncoding -> "UTF-8"]

(* heading levels inside a chapter notebook: H2..H5 -> Subsection..Sub^4section.
   H1 is reserved for the chapter title (rendered as the Section cell). *)
$chapterHeadingStyle = <|
    2 -> "Subsection",
    3 -> "Subsubsection",
    4 -> "Subsubsubsection",
    5 -> "Subsubsubsubsection"
|>

(* H2 titles that select a named back-matter section style (case-insensitive,
   trimmed). The value is the SectionStyle plus the body-cell context the
   section renders in. *)
$reservedH2 = <|
    "summary"               -> "Summary",
    "vocabulary"            -> "Vocabulary",
    "vocab"                 -> "Vocabulary",
    "key concepts"          -> "KeyConcepts",
    "key terms"             -> "KeyConcepts",
    "exercises"             -> "Exercises",
    "exercise"              -> "Exercises",
    "q&a"                   -> "QA",
    "q & a"                 -> "QA",
    "q and a"               -> "QA",
    "questions"             -> "QA",
    "questions and answers" -> "QA",
    "tech notes"            -> "TechNotes",
    "technical notes"       -> "TechNotes",
    "more to explore"       -> "MoreExplore",
    "more"                  -> "MoreExplore",
    "further reading"       -> "MoreExplore",
    "references"            -> "References",
    "bibliography"          -> "References",
    "resources"             -> "Resources",
    "takeaways"             -> "Takeaways",
    "key points"            -> "Takeaways"
|>

reservedSectionKindOf[heading_String] := Lookup[$reservedH2,
    ToLowerCase[StringTrim[heading]], None]

(* the chapter's Section heading: the canonical "<counter> | <title>" shape the
   palette's New Chapter dialog writes (CounterBox + SectionBar separator +
   title), with CounterAssignments resetting Section / Subsection /
   Subsubsection / Exercise counters at the start of the chapter. *)
chapterSectionCell[title_String, num_Integer] := Cell[
    TextData[Join[
        {CounterBox["Section"], StyleBox[" | ", "SectionBar"]},
        inlineTextData[title]
    ]],
    "Section",
    CounterAssignments -> {
        {"Section", num - 1}, {"Subsection", 0},
        {"Subsubsection", 0}, {"Exercise", 0}
    }
]
chapterSectionCell[title_String, _] := Cell[
    TextData[Join[{StyleBox[" | ", "SectionBar"]}, inlineTextData[title]]],
    "Section"
]

(* a normal Input/Output pair re-styled to a given pair of styles (e.g.
   ExerciseInput/ExerciseOutput, SolvedExampleInput/SolvedExampleOutput,
   TechNoteInput/TechNoteOutput). Mirrors exampleIO but with custom styles
   and without numbered In[]/Out[] labels - the book style sheets don't
   carry those for the alt code styles. *)
styledIOCells[block_, inStyle_String, outStyle_String] := Block[{
    outBoxes = Lookup[block, "OutputBoxes", Missing[]],
    code = block["Code"], inCell, outCell,
    msgs = Lookup[block, "Messages", {}],
    prints = Lookup[block, "Prints", {}]
},
    inCell = Cell[BoxData[inputBoxes[code]], inStyle];
    Which[
        MissingQ[outBoxes] || outBoxes === Null,
            Flatten[{inCell, asPrintCell /@ prints, messageCell /@ msgs}],
        True,
            outCell = Cell[BoxData[outBoxes], outStyle];
            {Cell[CellGroupData[
                Flatten[{inCell, asPrintCell /@ prints, messageCell /@ msgs, outCell}],
                Open
            ]]}
    ]
]

(* "free-form" body cells - the cells produced inside an ordinary subsection
   (i.e. one whose H2 isn't a reserved back-matter title), or inside the
   chapter's introduction (the prose between the chapter heading and the
   first H2). Mirrors defaultNotebook's per-block dispatch with book styles
   substituted (Item/Subitem nested by list depth, CodeText for a colon-
   ending prose line preceding an Input). The "counter" reference is shared
   with the rest of the chapter (each evaluated Input gets the next In[n] /
   Out[n] number, increasing through the whole notebook). *)
$bookListLevel = 1
$bookListStyle[1] = "Item"
$bookListStyle[2] = "Subitem"
$bookListStyle[_] = "Subsubitem"

bookProseCell[block_, nextBlockType_String] := Block[{text = block["Text"]},
    If[StringEndsQ[StringTrim[text], ":"] &&
        ! StringContainsQ[text, "\n"] && nextBlockType === "Code",
        Cell[TextData @ inlineTextData[text], "CodeText"],
        Cell[TextData @ inlineTextData[text], "Text"]
    ]
]

(* free-form (subsection-level) cell from a block. `next` is the type of the
   following block (used to decide CodeText vs Text for caption-like prose). *)
bookFreeCells[block_, next_String, counterSym_] := Switch[block["Type"],
    "Heading",
        {Cell[headingText[block["Text"]],
            Lookup[$chapterHeadingStyle, block["Level"], "Subsubsubsection"]]},
    "Prose",
        {bookProseCell[block, next]},
    "List",
        listItemCells[block, "Item"],
    "Table",
        {tableCell[block]},
    "Quote",
        {quoteCell[block["Text"]]},
    "MathBlock",
        {mathBlockCell[block["Text"]]},
    "Image",
        {imageCell[block]},
    "Code",
        If[ executableQ[block],
            $chapterCounter += 1;
            exampleIOFor[block, $chapterCounter],
            withCellFlag[block, {nonExecutableCell[block]}]
        ],
    "Div",
        bookDivCells[block, counterSym],
    "Separator",
        {exampleDelimiterCell},
    _, {}
]

(* the fenced-div dispatch: each ::: kind opens one of the Book Tools
   multi-cell scaffolds. Kinds we handle: solved-example, theorem,
   theorem-numbered, proof, exercise, solution. Anything else falls back to
   rendering the inner blocks as plain free-form cells. *)
bookDivCells[block_, counterSym_] := Block[{
    kind = ToLowerCase[StringTrim[StringReplace[block["Kind"], "_" -> "-"]]],
    inner = block["Blocks"]
},
    Switch[kind,
        "solved-example",       solvedExampleCells[inner, counterSym, False],
        "solved-example-numbered", solvedExampleCells[inner, counterSym, True],
        "theorem",              theoremCells[inner, counterSym, False],
        "theorem-numbered",     theoremCells[inner, counterSym, True],
        "proof",                proofCells[inner, counterSym, False],
        "proof-numbered",       proofCells[inner, counterSym, True],
        "exercise",             exerciseDivCells[inner, counterSym],
        "solution",             solutionDivCells[inner, counterSym],
        _,
            Flatten[Map[
                bookFreeCells[#, "", counterSym] &,
                inner
            ]]
    ]
]

(* SolvedExample scaffold. The first non-code inner block is the lead-in
   that becomes the SolvedExampleNote, the inner ``wl`` blocks become
   SolvedExampleInput / SolvedExampleOutput, and any inner display math
   becomes SolvedExampleDisplayFormula(Numbered). A SolvedExampleEndCap
   terminates the group. If `numbered`, the heading carries CounterBox
   counters; otherwise it's just titled "Solved Example" plus the lead-in. *)
solvedExampleCells[inner_List, counterSym_, numbered_] := Block[{
    headBlock, restBlocks, headTextData, headCell
},
    {headBlock, restBlocks} = If[
        inner =!= {} && First[inner]["Type"] === "Prose",
        {First[inner], Rest[inner]},
        {<|"Type" -> "Prose", "Text" -> "Solved Example"|>, inner}
    ];
    headTextData = If[numbered,
        Join[inlineTextData[headBlock["Text"] <> " "],
            {CounterBox["Section"], ".", CounterBox["SolvedExample"]}],
        inlineTextData[headBlock["Text"]]
    ];
    headCell = Cell[TextData[headTextData], "SolvedExample"];
    Join[
        {headCell},
        Flatten @ Map[bookSolvedInnerCells[#, counterSym] &, restBlocks],
        {Cell["", "SolvedExampleEndCap"]}
    ]
]

bookSolvedInnerCells[block_, counterSym_] := Switch[block["Type"],
    "Prose",
        {Cell[TextData @ inlineTextData[block["Text"]], "SolvedExampleNote"]},
    "Code",
        If[ executableQ[block],
            styledIOCells[block, "SolvedExampleInput", "SolvedExampleOutput"],
            {Cell[block["Code"], "SolvedExampleInput"]}
        ],
    "MathBlock",
        With[{nm = Lookup[block, "Numbered", False]},
            {Cell[BoxData[PaneBox[
                Replace[texBoxes[block["Text"]], $Failed ->
                    FormBox[inputBoxes[block["Text"]], TraditionalForm]],
                ImageSize -> Full, Alignment -> Center]],
                If[TrueQ[nm], "SolvedExampleDisplayFormulaNumbered",
                    "SolvedExampleDisplayFormula"]]}
        ],
    "List",
        listItemCells[block, "Item"],
    _, bookFreeCells[block, "", counterSym]
]

(* Theorem scaffold: a Theorem heading (with CounterBox counters when
   numbered), then a TheoremStatement (the first prose paragraph if any),
   then any further inner blocks rendered as free-form cells. The
   ProofTheoremEndCap terminates the group only when nested under a Proof. *)
theoremCells[inner_List, counterSym_, numbered_] := Block[{
    headBlock, restBlocks, headTextData, headCell, statementCell, rest
},
    {headBlock, restBlocks} = If[
        inner =!= {} && First[inner]["Type"] === "Prose",
        {First[inner], Rest[inner]},
        {<|"Type" -> "Prose", "Text" -> "Theorem"|>, inner}
    ];
    headTextData = If[numbered,
        Join[inlineTextData[headBlock["Text"] <> " "],
            {CounterBox["Section"], ".", CounterBox["Subsection"]}],
        inlineTextData[headBlock["Text"]]
    ];
    headCell = Cell[TextData[headTextData], "Theorem"];
    (* split the statement cell out of restBlocks without using a multi-
       assignment - {Nothing, x} would auto-collapse to {x} and break Set. *)
    If[restBlocks =!= {} && First[restBlocks]["Type"] === "Prose",
        statementCell = Cell[TextData @ inlineTextData[First[restBlocks]["Text"]],
            "TheoremStatement"];
        rest = Rest[restBlocks]
    ,
        statementCell = Nothing;
        rest = restBlocks
    ];
    Join[{headCell, statementCell},
        Flatten @ Map[bookFreeCells[#, "", counterSym] &, rest]]
]

proofCells[inner_List, counterSym_, numbered_] := Block[{contentCells},
    contentCells = Flatten @ Map[bookProofInnerCells[#, counterSym] &, inner];
    Join[{Cell["Proof", "Proof"]}, contentCells,
        {Cell["", "ProofTheoremEndCap"]}]
]

bookProofInnerCells[block_, counterSym_] := Switch[block["Type"],
    "Prose",
        {Cell[TextData @ inlineTextData[block["Text"]], "ProofContent"]},
    "MathBlock",
        {Cell[BoxData[PaneBox[
            Replace[texBoxes[block["Text"]], $Failed ->
                FormBox[inputBoxes[block["Text"]], TraditionalForm]],
            ImageSize -> Full, Alignment -> Center]],
            "ProofTheoremDisplayFormula"]},
    _, bookFreeCells[block, "", counterSym]
]

(* one Exercise. The first prose line becomes the Exercise prompt cell;
   subsequent prose/code/list/math blocks render in the Exercise context
   (paragraphs -> ExerciseNote, ``wl`` -> ExerciseInput/ExerciseOutput).
   A nested ::: solution div opens the ExerciseSolution group. *)
exerciseDivCells[inner_List, counterSym_] := Block[{
    promptBlock, rest, promptCell
},
    {promptBlock, rest} = If[
        inner =!= {} && First[inner]["Type"] === "Prose",
        {First[inner], Rest[inner]},
        {<|"Type" -> "Prose", "Text" -> "Exercise"|>, inner}
    ];
    promptCell = Cell[TextData @ inlineTextData[promptBlock["Text"]],
        "Exercise"];
    Prepend[
        Flatten @ Map[bookExerciseInnerCells[#, counterSym] &, rest],
        promptCell
    ]
]

bookExerciseInnerCells[block_, counterSym_] := Switch[block["Type"],
    "Prose",
        {Cell[TextData @ inlineTextData[block["Text"]], "ExerciseNote"]},
    "Code",
        If[ executableQ[block],
            styledIOCells[block, "ExerciseInput", "ExerciseOutput"],
            {Cell[block["Code"], "ExerciseInput"]}
        ],
    "List",
        listItemCells[block, "Item"],
    "MathBlock",
        {mathBlockCell[block["Text"]]},
    "Div",
        If[ToLowerCase[StringTrim[block["Kind"]]] === "solution",
            solutionDivCells[block["Blocks"], counterSym],
            bookDivCells[block, counterSym]
        ],
    _, bookFreeCells[block, "", counterSym]
]

solutionDivCells[inner_List, counterSym_] := Join[
    {Cell["Solution", "ExerciseSolution"]},
    Flatten @ Map[bookSolutionInnerCells[#, counterSym] &, inner]
]

bookSolutionInnerCells[block_, counterSym_] := Switch[block["Type"],
    "Prose",
        {Cell[TextData @ inlineTextData[block["Text"]], "SolutionAnswer"]},
    "Code",
        If[ executableQ[block],
            styledIOCells[block, "ExerciseInput", "ExerciseOutput"],
            {Cell[block["Code"], "ExerciseInput"]}
        ],
    "List",
        Map[Cell[TextData @ inlineTextData[#], "SolutionItem"] &,
            block["Items"]],
    _, bookFreeCells[block, "", counterSym]
]

(* === reserved back-matter sections === *)

(* group consecutive blocks under H2 boundaries. Returns a list of
   {<heading or None>, {blocks}} pairs. The first group has heading None
   if there is intro content before the first H2; subsequent groups carry
   their H2 heading block as the first element. *)
groupByH2[blocks_List] := Block[{groups = {}, current = None, currentBlocks = {}, finalize},
    finalize[h_, bs_] := AppendTo[groups, {h, bs}];
    Do[
        If[b["Type"] === "Heading" && b["Level"] === 2,
            finalize[current, currentBlocks];
            current = b; currentBlocks = {},
            AppendTo[currentBlocks, b]
        ],
        {b, blocks}
    ];
    finalize[current, currentBlocks];
    DeleteCases[groups, {None, {}}]
]

(* Summary section: heading -> SummarySection; paragraphs -> SummaryNote;
   bullets -> SummaryList. *)
summarySectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {Cell[TextData @ inlineTextData[b["Text"]], "SummaryNote"]},
            "List",  listItemCells[b, "SummaryList"],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "SummarySection"]
]

(* Vocabulary: a 2-column pipe table becomes a VocabularyTable GridBox;
   anything else renders free-form (so subsection headings nested inside
   vocab still work). *)
vocabularyTableCellFromTable[block_] := Cell[
    BoxData[GridBox[
        Map[
            row |-> {RowBox[{
                row[[1]], " ",
                Cell[row[[2]], "VocabularyText"]
            }]},
            block["Rows"]
        ]
    ]],
    "VocabularyTable"
]

vocabularySectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Table",
                {vocabularyTableCellFromTable[b]},
            "Prose",
                {Cell[TextData @ inlineTextData[b["Text"]], "Text"]},
            "Heading",
                {Cell[headingText[b["Text"]],
                    Switch[b["Level"],
                        3, "VocabularySubsection",
                        4, "VocabularySubsubsection",
                        _, "VocabularySubsection"]]},
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "VocabularySection"]
]

(* KeyConcepts: a "Key Concepts" / "Key Terms" H2 - renders the heading as
   a regular Subsection and the bulleted list as plain Items (the EIWL-style
   "things you'll learn" bullet list at the top of a chapter). *)
keyConceptsSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[bookFreeCells[#, "", counterSym] &, blocks],
    Cell[headingText[heading["Text"]], "Subsection"]
]

(* Exercises: heading -> ExerciseSection; H3 -> ExerciseSubsection; each
   "::: exercise" div is one Exercise group; bare ordered-list items
   collapse to single-line Exercise cells. *)
exercisesSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Heading",
                {Cell[headingText[b["Text"]],
                    If[b["Level"] === 3, "ExerciseSubsection",
                        Lookup[$chapterHeadingStyle, b["Level"],
                            "Subsubsection"]]]},
            "Prose",
                {Cell[TextData @ inlineTextData[b["Text"]],
                    "ExerciseSectionNote"]},
            "List",
                Map[Cell[TextData @ inlineTextData[#], "Exercise"] &,
                    b["Items"]],
            "Div",
                bookDivCells[b, counterSym],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "ExerciseSection"]
]

(* Q&A: heading -> QASection; paragraph that starts with Q. / Q: / Q -
   trims that lead-in and becomes a Question; same for A. -> Answer.
   Anything else falls through to a plain Text cell. *)
qaProseCell[text_String] := Block[{trimmed = StringTrim[text]},
    Which[
        StringMatchQ[trimmed, ("Q." | "Q:" | "Q -" | "**Q.**" | "**Q:**") ~~ Whitespace ~~ ___],
            Cell[TextData @ inlineTextData @ StringTrim @
                StringReplace[trimmed,
                    StartOfString ~~ ("**Q.**" | "**Q:**" | "Q." | "Q:" | "Q -") ~~ Whitespace -> ""],
                "Question"],
        StringMatchQ[trimmed, ("A." | "A:" | "A -" | "**A.**" | "**A:**") ~~ Whitespace ~~ ___],
            Cell[TextData @ inlineTextData @ StringTrim @
                StringReplace[trimmed,
                    StartOfString ~~ ("**A.**" | "**A:**" | "A." | "A:" | "A -") ~~ Whitespace -> ""],
                "Answer"],
        True,
            Cell[TextData @ inlineTextData[text], "Text"]
    ]
]

qaSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {qaProseCell[b["Text"]]},
            "List",  listItemCells[b, "Item"],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "QASection"]
]

(* Tech Notes: heading -> TechNoteSection; paragraphs -> TechNote; code ->
   TechNoteInput/Output; list items -> TechNoteItem. *)
techNotesSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {Cell[TextData @ inlineTextData[b["Text"]], "TechNote"]},
            "Code",
                If[ executableQ[b],
                    styledIOCells[b, "TechNoteInput", "TechNoteOutput"],
                    {Cell[b["Code"], "TechNoteInput"]}
                ],
            "List",
                Map[Cell[TextData @ inlineTextData[#], "TechNoteItem"] &,
                    b["Items"]],
            "MathBlock", {mathBlockCell[b["Text"]]},
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "TechNoteSection"]
]

(* More to Explore: heading -> MoreExploreSection; bullets -> MoreExplore;
   bare-URL prose -> MoreExploreShortURL. *)
moreExploreCell[text_String] := Cell[TextData @ inlineTextData[text],
    If[StringMatchQ[StringTrim[text], ("http" ~~ ___) | ("wolfr.am/" ~~ ___)],
        "MoreExploreShortURL", "MoreExplore"]
]

moreExploreSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {moreExploreCell[b["Text"]]},
            "List",
                Map[Cell[TextData @ inlineTextData[#], "MoreExplore"] &,
                    b["Items"]],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "MoreExploreSection"]
]

(* References: heading -> ReferenceSection; bullets / paragraphs ->
   Reference cells. *)
referencesSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {Cell[TextData @ inlineTextData[b["Text"]], "Reference"]},
            "List",
                Map[Cell[TextData @ inlineTextData[#], "Reference"] &,
                    b["Items"]],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "ReferenceSection"]
]

resourcesSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {Cell[TextData @ inlineTextData[b["Text"]], "ResourcesText"]},
            "List",
                Map[Cell[TextData @ inlineTextData[#], "ResourcesText"] &,
                    b["Items"]],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "ResourcesSubsection"]
]

takeawaysSectionCells[heading_, blocks_, counterSym_] := Prepend[
    Catenate @ Map[
        b |-> Switch[b["Type"],
            "Prose", {Cell[TextData @ inlineTextData[b["Text"]], "TakeawaysText"]},
            "List",
                Map[Cell[TextData @ inlineTextData[#], "TakeawaysText"] &,
                    b["Items"]],
            _, bookFreeCells[b, "", counterSym]
        ],
        blocks
    ],
    Cell[headingText[heading["Text"]], "TakeawaysSection"]
]

(* dispatch: given an H2 heading block (or None) plus its body blocks,
   build the cells for that group. None means "intro content before the
   first H2" - emit it as free-form cells. *)
chapterGroupCells[None, blocks_, counterSym_] :=
    Block[{next, out = {}},
        Do[
            next = If[i < Length[blocks], blocks[[i + 1]]["Type"], ""];
            out = Join[out, bookFreeCells[blocks[[i]], next, counterSym]],
            {i, Length[blocks]}
        ];
        out
    ]
chapterGroupCells[heading_Association, blocks_, counterSym_] := Block[{
    kind = reservedSectionKindOf[heading["Text"]], next, out
},
    Switch[kind,
        "Summary",      summarySectionCells[heading, blocks, counterSym],
        "Vocabulary",   vocabularySectionCells[heading, blocks, counterSym],
        "KeyConcepts",  keyConceptsSectionCells[heading, blocks, counterSym],
        "Exercises",    exercisesSectionCells[heading, blocks, counterSym],
        "QA",           qaSectionCells[heading, blocks, counterSym],
        "TechNotes",    techNotesSectionCells[heading, blocks, counterSym],
        "MoreExplore",  moreExploreSectionCells[heading, blocks, counterSym],
        "References",   referencesSectionCells[heading, blocks, counterSym],
        "Resources",    resourcesSectionCells[heading, blocks, counterSym],
        "Takeaways",    takeawaysSectionCells[heading, blocks, counterSym],
        _,
            out = {Cell[headingText[heading["Text"]], "Subsection"]};
            Do[
                next = If[i < Length[blocks], blocks[[i + 1]]["Type"], ""];
                out = Join[out, bookFreeCells[blocks[[i]], next, counterSym]],
                {i, Length[blocks]}
            ];
            out
    ]
]

(* `counterSym` is a Block-local symbol so the nested helpers can SetDelayed
   on it (the value mutates as wl example cells get In[n]/Out[n] labels).
   We carry it as an explicit argument through the section dispatchers so
   each is closure-free. *)
chapterNotebook[data_] := Block[{
    meta = data["meta"], blocks = data["blocks"],
    title, chapterNum, groups, bodyCells, $chapterCounter = 0, frontmatterOpts,
    firstH1, contentBlocks
},
    (* Drop the H1 heading from the body: the chapter title is the Section
       heading we emit ourselves, not a Subsection/.. inside the chapter.
       Fall back to the H1 text for the title when Name: is absent. *)
    firstH1 = SelectFirst[blocks,
        # =!= Null && #["Type"] === "Heading" && #["Level"] === 1 &, Null];
    contentBlocks = DeleteCases[blocks,
        b_ /; AssociationQ[b] && b["Type"] === "Heading" && b["Level"] === 1];
    title = Lookup[meta, "Name", Lookup[meta, "Title",
        If[firstH1 =!= Null, firstH1["Text"], ""]]];
    chapterNum = With[{n = Lookup[meta, "ChapterNumber", Missing[]]},
        Which[
            IntegerQ[n], n,
            StringQ[n] && StringMatchQ[StringTrim[n], DigitCharacter ..],
                ToExpression[StringTrim[n]],
            True, Missing[]
        ]
    ];
    (* a Title-style banner above the chapter heading - used only when a
       Subtitle frontmatter key is set, to mimic the palette's optional
       Subchapter cell. The chapter title itself always renders as the
       Section heading. *)
    groups = groupByH2[contentBlocks];
    bodyCells = Catenate @ Map[
        chapterGroupCells[#[[1]], #[[2]], $chapterCounter] &,
        groups
    ];
    frontmatterOpts = DeleteCases[{
        With[{pw = Lookup[meta, "PageWidth", Inherited]},
            If[NumericQ[pw], PageWidth -> pw, Nothing]],
        With[{spb = Lookup[meta, "ShowPageBreaks", Inherited]},
            If[BooleanQ[spb], ShowPageBreaks -> spb, Nothing]]
    }, Nothing];
    Notebook[
        Join[
            {chapterSectionCell[title,
                Replace[chapterNum, Except[_Integer] -> 0]]},
            If[Lookup[meta, "Subtitle", ""] =!= "",
                {Cell[Lookup[meta, "Subtitle", ""], "Subchapter"]}, {}],
            bodyCells
        ],
        StyleDefinitions -> $bookStyleSheet,
        Sequence @@ frontmatterOpts
    ]
]

buildNotebook["FunctionResource", data_] := resourceNotebook["Function", data]
buildNotebook["Paclet", data_] := resourceNotebook["Paclet", data]
buildNotebook["Example", data_] := resourceNotebook["Example", data]
buildNotebook["Data", data_] := resourceNotebook["Data", data]
buildNotebook["Prompt", data_] := resourceNotebook["Prompt", data]
buildNotebook["Demonstration", data_] := resourceNotebook["Demonstration", data]
buildNotebook["Symbol", data_] := symbolNotebook[data]
buildNotebook["Guide", data_] := guideNotebook[data]
buildNotebook["TechNote", data_] := tutorialNotebook[data]
buildNotebook["Overview", data_] := overviewNotebook[data]
buildNotebook["ComputationalEssay", data_] := essayNotebook[data]
buildNotebook["Essay", data_] := essayNotebook[data]
buildNotebook["Chapter", data_] := chapterNotebook[data]
buildNotebook["BookChapter", data_] := chapterNotebook[data]
buildNotebook["LLMTool", data_] := resourceNotebook["LLMTool", data]
buildNotebook["Format", data_] := refSubtypeNotebook["Format", data]
buildNotebook["ServiceConnection", data_] := refSubtypeNotebook["ServiceConnection", data]
buildNotebook["Device", data_] := refSubtypeNotebook["Device", data]
buildNotebook["Interpreter", data_] := refSubtypeNotebook["Interpreter", data]
buildNotebook["Entity", data_] := refSubtypeNotebook["Entity", data]
buildNotebook["Character", data_] := refSubtypeNotebook["Character", data]
buildNotebook["Message", data_] := refSubtypeNotebook["Message", data]
buildNotebook["Program", data_] := refSubtypeNotebook["Program", data]
buildNotebook["Workflow", data_] := workflowNotebook[data]
buildNotebook["WorkflowGuide", data_] := workflowGuideNotebook[data]
buildNotebook[_, data_] := defaultNotebook[data]

(* Every cell needs a CellID for the resource scraper to locate the definition and
   example cells. The interactive front end normally stamps the missing CellIDs
   (and a fresh ExpressionUUID per cell) when the notebook is first opened - both
   drawn from system randomness, so two builds of the same source, or the same
   build opened twice, produce different notebooks. To keep MarkdownToNotebook
   DETERMINISTIC (reproducible builds, diffable output, stable scraper / annotation
   IDs) we assign the CellIDs ourselves (from each cell's structural position) and
   normalize the ExpressionUUIDs that Export injects (below), and drop CreateCellID
   so the front end does not re-randomize what we set. *)

(* Stamp a CellID on each STRUCTURAL cell (a notebook / cell-group member) that
   lacks one - never on the inline cells nested inside a cell's content, which
   carry no CellID. The key is the cell's structural path: unique within the
   notebook and stable across rebuilds. Cells that already carry a CellID (e.g.
   the Hash-keyed link items, fillLinkCells) keep it. Export[..., "NB"] preserves
   CellIDs, so stamping them on the expression is enough. *)
stampCellID[Cell[CellGroupData[inner_List, gopts___], copts___], idx_] :=
    Cell[CellGroupData[MapIndexed[stampCellID[#1, Join[idx, #2]] &, inner], gopts], copts]
stampCellID[Cell[content_, style_String, opts___], idx_] :=
    If[FreeQ[{opts}, CellID],
        Cell[content, style, opts, CellID -> Hash[Prepend[idx, "MTNCellID"]]],
        Cell[content, style, opts]]
stampCellID[other_, _] := other

withDeterministicIDs[Notebook[cells_List, o : OptionsPattern[]]] :=
    Notebook[MapIndexed[stampCellID[#1, #2] &, cells],
        Sequence @@ FilterRules[{o}, Except[CreateCellID]]]
withDeterministicIDs[other_] := other

(* ExpressionUUIDs are the other half of the non-determinism, but unlike CellIDs
   they are NOT in the built expression - Export[..., "NB"] stamps a fresh RANDOM
   one on every cell as it serializes. So we normalize them in the exported text:
   rewrite each ExpressionUUID string with a value keyed by its occurrence order
   (deterministic, since Export's cell order is fixed for a given expression).
   This preserves Export's canonical .nb header / options / stylesheet exactly -
   only the id strings change. *)
deterministicUUID[n_Integer] := StringInsert[
    IntegerString[Hash[{"MTNuuidHi", n}], 16, 16] <> IntegerString[Hash[{"MTNuuidLo", n}], 16, 16],
    "-", {9, 13, 17, 21}]

deterministicUUIDText[txt_String] := Module[{i = 0},
    StringReplace[txt,
        pre : ("ExpressionUUID" ~~ WhitespaceCharacter ... ~~ "->" ~~ WhitespaceCharacter ... ~~ "\"") ~~
            Except["\""] .. ~~ "\"" :> (pre <> deterministicUUID[i++] <> "\"")]]

exportDeterministicNB[spec_, nb_] := (
    Export[spec, nb, "NB"];
    Export[spec, deterministicUUIDText @ Import[spec, "Text"], "Text"];
    spec)

(* === markdown-out: a rendered markdown twin ===
   MarkdownToNotebook[source, "out.md"] re-serializes the document to markdown but
   follows each evaluated wl cell with an image of its output, saved under images/
   beside the target. The twin is the rendered, viewer-ready version: prose,
   headings, lists, tables, frontmatter, and every evaluated output - and nothing
   else. Notebook-side cell options ("#| file: ...", "#| screenshot: true",
   "#| tear: 200", "#| eval: false", "#| flag: ...") are stripped, since they
   carry processing directives the rendered view has no use for (the file include
   is already expanded, the screenshot is already there, etc.). Inferred [Symbol]()
   links are resolved to public web URLs (paclet:Wolfram/AccessibleColors/ref/X ->
   https://resources.wolframcloud.com/PacletRepository/... ; bare System symbols ->
   their reference.wolfram.com page) so every link clicks through on GitHub. *)
(* quote a YAML value when it would otherwise break parsing: brackets / braces /
   commas open a flow collection, ": " or " #" end a scalar, and a leading
   indicator char reads as a node tag. A markdown link "[label](url)" in a [list]
   hits the bracket case, so the source's quotes (which the YAML parser strips on
   the way in) must be restored on the way out, or GitHub rejects the frontmatter. *)
yamlNeedsQuote[s_String] := StringContainsQ[s, "[" | "]" | "{" | "}" | "," | ": " | " #" | "\""] ||
    StringStartsQ[s, "[" | "{" | "&" | "*" | "!" | "|" | ">" | "@" | "`" | "%" | "'" | "\"" | "#"] ||
    s =!= StringTrim[s]
yamlValue[s_String] := If[yamlNeedsQuote[s], "\"" <> StringReplace[s, {"\\" -> "\\\\", "\"" -> "\\\""}] <> "\"", s]
yamlValue[x_] := ToString[x]

fmLine[k_, v_String] := k <> ": " <> yamlValue[v]
fmLine[k_, v_List] := k <> ": [" <> StringRiffle[yamlValue /@ v, ", "] <> "]"
fmLine[k_, v_] := k <> ": " <> ToString[v]

serializeFrontmatter[meta_] := If[meta === <||> || meta === Null, "",
    "---\n" <> StringRiffle[KeyValueMap[fmLine, meta], "\n"] <> "\n---\n"]

serializeTableMd[block_] := StringRiffle[Join[
    {"| " <> StringRiffle[block["Header"], " | "] <> " |",
     "|" <> StringRiffle[ConstantArray["---", Length[block["Header"]]], "|"] <> "|"},
    ("| " <> StringRiffle[#, " | "] <> " |") & /@ block["Rows"]
], "\n"]

(* write the rasterized image only if it differs pixel-wise from what's on disk:
   PNG re-encoding is non-deterministic at the byte level (compression / timestamps),
   so two visually identical re-renders would otherwise show as "modified" and churn
   git history. Compare raw byte ImageData (dimensions first, as a cheap reject). *)
writeImageIfChanged[path_String, img_] := Block[{existing},
    existing = If[FileExistsQ[path], Quiet @ Import[path], None];
    If[ ImageQ[existing] && ImageQ[img] &&
        ImageDimensions[existing] === ImageDimensions[img] &&
        ImageData[existing, "Byte"] === ImageData[img, "Byte"],
        path,
        Quiet @ Export[path, img, "PNG"]; path
    ]
]

(* Sections whose .nb rendering is input-only (no Output cell shown next
   to the input): the resource definition cell, the verification tests,
   the content elements of a Data resource. The .nb still evaluates
   these cells (the rest of the document needs the resulting bindings),
   but the published page never shows their outputs - so the twin .md
   shouldn't either. *)
$inputOnlyTwinSections = {"definition", "tests", "content"}

markdownWithImages[blocks_, meta_, target_String] := Block[{dir, base, imgDir, n = 0, currentSection = "", mdOf, codeMd},
    dir = DirectoryName[target]; base = FileBaseName[target];
    imgDir = FileNameJoin[{dir, "images"}];
    Quiet @ CreateDirectory[imgDir, CreateIntermediateDirectories -> True];
    codeMd[b_] := Block[{fence, imgFile, img, msgs, msgBlock, prints, prtBlock, outsList, outsBlock, suppressOuts},
        suppressOuts = MemberQ[$inputOnlyTwinSections, currentSection];
        (* twin keeps no "#| key: value" cell options - those are notebook-side
           evaluation directives (file, screenshot, tear, eval, flag) that have
           no rendered meaning. The file include is already expanded into
           b["Code"] by resolveIncludes, so the twin shows the actual code. *)
        fence = "```" <> b["Lang"] <> "\n" <> b["Code"] <> "\n```";
        (* captured kernel messages render as plain markdown blockquote admonitions
           (one per message) so a stray Power::infy or Part::partw shows up in the
           viewer right next to the cell that fired it - the twin had been silent
           about them, hiding real errors behind a tidy-looking output image.
           Captured Print / Echo output renders the same way, between the fence
           and any messages, so a `Print["loaded N entries"]` shows up as a
           visible stdout breadcrumb in the twin. *)
        prints = If[KeyExistsQ[b, "Prints"], b["Prints"], {}];
        (* a textual Print renders as a blockquote (same shape as a
           message); a rich Print (Print[graphic] / Print[dataset] / ...)
           rasterises to its own PNG and embeds inline, the same way an
           Output cell does. *)
        prtBlock = If[prints === {} || MissingQ[prints], "",
            StringJoin @ Map[
                With[{tf = printTextForm[#]},
                    If[ StringQ[tf],
                        "\n\n" <> messageMd[tf],
                        n += 1; imgFile = base <> "-" <> ToString[n] <> ".png";
                        img = UsingFrontEnd @ Rasterize[
                            Notebook[{# /. Cell[c_, "Print", o___] :> Cell[c, "Output", o]}, LightDark -> $lightDark, StyleDefinitions -> "Default.nb"],
                            ImageResolution -> 96];
                        writeImageIfChanged[FileNameJoin[{imgDir, imgFile}], img];
                        "\n\n![print](images/" <> imgFile <> ")"
                    ]
                ] &,
                prints]];
        msgs = If[KeyExistsQ[b, "Messages"], b["Messages"], {}];
        msgBlock = If[msgs === {} || MissingQ[msgs], "",
            "\n\n" <> StringRiffle[DeleteCases[messageMd /@ msgs, ""], "\n\n"]];
        (* per-statement outputs: a cell with `1+1\n2+2` produces two output
           images, one per non-suppressed value. Empty outsList -> no images
           (a cell whose only statements were `;`-suppressed). Suppressed
           entirely for sections whose .nb is input-only (see
           $inputOnlyTwinSections). *)
        outsList = If[suppressOuts, {}, Replace[Lookup[b, "Outputs", Automatic], Automatic :> {b["OutputBoxes"]}]];
        outsList = DeleteCases[outsList, _?MissingQ | Null];
        outsBlock = StringJoin @ Map[
            (n += 1; imgFile = base <> "-" <> ToString[n] <> ".png";
                img = UsingFrontEnd @ Rasterize[
                    Notebook[{Cell[BoxData[#], "Output", Sequence @@ extraOutputOpts[b]]}, LightDark -> $lightDark, StyleDefinitions -> "Default.nb"],
                    ImageResolution -> 96];
                writeImageIfChanged[FileNameJoin[{imgDir, imgFile}], img];
                "\n\n![output](images/" <> imgFile <> ")") &,
            outsList];
        fence <> prtBlock <> msgBlock <> outsBlock
    ];
    mdOf[b_] := (
        (* track the current top-level section so codeMd can suppress
           output images in sections that are input-only in the .nb. *)
        If[b["Type"] === "Heading" && b["Level"] <= 2,
            currentSection = ToLowerCase[b["Text"]]
        ];
        Switch[b["Type"],
        "Heading", StringRepeat["#", b["Level"]] <> " " <> resolveWebRefs[b["Text"]],
        "Prose", resolveWebRefs[b["Text"]],
        "List", If[ TrueQ[b["Ordered"]],
            StringRiffle[MapIndexed[ToString[First[#2]] <> ". " <> resolveWebRefs[#1] &, b["Items"]], "\n"],
            StringRiffle["- " <> resolveWebRefs[#] & /@ b["Items"], "\n"]
        ],
        "Table", serializeTableMd[b],
        "Separator", "---",
        "Quote", "> " <> resolveWebRefs[b["Text"]],
        "MathBlock", "$$ " <> b["Text"] <> " $$",
        "Image", "![" <> Lookup[b, "Alt", ""] <> "](" <> Lookup[b, "Path", ""] <> ")",
        "Code", codeMd[b],
        "Div", "::: " <> b["Kind"] <> "\n\n" <>
            StringRiffle[DeleteCases[mdOf /@ b["Blocks"], ""], "\n\n"] <>
            "\n\n:::",
        _, ""
    ]);
    Export[target, serializeFrontmatter[meta] <> "\n" <> StringRiffle[DeleteCases[mdOf /@ blocks, ""], "\n\n"] <> "\n", "Text"];
    target
]

(* === example-output cache ===
   Evaluated example outputs are cached with the built-in persistence framework -
   a PersistentSymbol per cell, keyed by the cumulative code hash, at the "Local"
   location so it survives sessions. Pass "UseCache" -> False to ignore the cached
   contents and regenerate (e.g. after the documented library changed but the
   example code did not); otherwise manage it the standard way -
   PersistentObjects["MarkdownToNotebook/**"] to list, DeleteObject to clear, and
   $PersistencePath / PersistenceLocation to relocate. *)
$cacheLocation = "Local"

(* Sanitise a doc name for use in a PersistentObject path.  The frontmatter
   "Name" is the canonical identifier ("Wolfram/MyPaclet", "ReverseAddSequence",
   ...); we keep "/", "-", ".", "_" and word characters so the namespace path
   is hierarchical (a publisher-prefixed name like "Wolfram/MyPaclet" maps to a
   nested namespace) and replace anything else with "_".  Empty or all-special
   names fall back to "unnamed". *)
sanitiseDocNameForCache[s_String] := With[{
    cleaned = StringTrim[StringReplace[s, Except[WordCharacter | "-" | "." | "/"] -> "_"], "/"]
},
    If[cleaned === "", "unnamed", cleaned]
]
sanitiseDocNameForCache[_] := "unnamed"

(* Cache entry name: human-searchable per doc + per cell, content-addressed by
   the cumulative hash.  Layout

       MarkdownToNotebook/ExampleOutput/<DocName>/<NNN>-<hashB36>

   PersistentObjects["MarkdownToNotebook/ExampleOutput/Wolfram/MyPaclet/*",
   "Local"] returns every entry for that doc; cell-001/cell-002 sort
   lexicographically so the entries enumerate in evaluation order.  The
   hashB36 suffix preserves the content-addressing - changing a cell's code
   yields a new hash and a fresh entry; the previous stale entry orphans
   under the same NNN prefix and is easy to spot when grepping. *)
exampleCacheName[docName_String, cellIdx_Integer, h_Integer] :=
    "MarkdownToNotebook/ExampleOutput/" <>
        sanitiseDocNameForCache[docName] <>
        "/" <> IntegerString[cellIdx, 10, 3] <>
        "-" <> IntegerString[h, 36]

(* Store the entry Compress'd. PersistentSymbol serializes via Put, which renders an
   embedded raw format-wrapper expression (TraditionalForm[...] / OutputForm[...], as
   Interpretation / Manipulate / DynamicModule outputs carry) as 2D text - fraction
   bars, "cos(...)" - that Get can no longer parse (Syntax::sntx), so the entry reads
   back Missing and, since allHit needs every entry, the whole doc re-evaluates on
   every warm build and re-poisons the entry (issue #60). Compress round-trips any
   expression as an opaque ASCII string. Legacy uncompressed entries (an Association,
   not a String) pass through unchanged. *)
exampleCacheGet[name_String] := Replace[PersistentSymbol[name, $cacheLocation], c_String :> Uncompress[c]]
exampleCacheSet[name_String, v_] := (PersistentSymbol[name, $cacheLocation] = Compress[v];)

(* === entry point === *)

(* the result is chosen by the optional second argument:
     MarkdownToNotebook[source]                -> the Notebook expression
     MarkdownToNotebook[source, "Notebook"]    -> the Notebook expression
     MarkdownToNotebook[source, "Association"] -> the parsed structure
     MarkdownToNotebook[source, "out.md"]      -> a rendered markdown twin: the
        document re-serialized with each wl output added as an image under images/
     MarkdownToNotebook[source, file]          -> write the notebook to file, return it
   ("Notebook"/"Association" are reserved; a ".md" target writes markdown; any other
   string is a notebook file path.) The layout comes from the Template frontmatter. *)
(* "PreserveSource" -> True stamps the produced notebook with the original
   markdown source under TaggingRules -> {..., "MarkdownToNotebook" -> <|
   "Source" -> ..., "Template" -> ...|>}. The default is False so that a
   notebook is a strictly-rendered artifact - any post-conversion edit to
   the cells shows up faithfully when the inverse (NotebookToMarkdown) walks
   it back to markdown, which is the right semantics for diffing the edited
   .nb against the .md it was built from. With True, the .nb becomes
   self-contained (rendered view + the markdown source it came from in one
   file), useful for tooling that wants the source side-loaded without
   re-parsing the cells. NotebookToMarkdown does NOT read this stash - by
   design, the walker runs on every input. *)
withMarkdownSource[Notebook[cells_, o : OptionsPattern[]], src_String, tmpl_String] := Block[
    {oldRules = Lookup[{o}, TaggingRules, {}], newEntry},
    newEntry = "MarkdownToNotebook" -> <|"Source" -> src, "Template" -> tmpl|>;
    Notebook[cells,
        TaggingRules -> If[ListQ[oldRules],
            Append[DeleteCases[oldRules, "MarkdownToNotebook" -> _], newEntry],
            {newEntry}
        ],
        Sequence @@ FilterRules[{o}, Except[TaggingRules]]
    ]
]
withMarkdownSource[other_, _, _] := other

Options[MarkdownToNotebook] = {"Evaluate" -> True, "PreserveSource" -> False, "EvaluateSeparator" -> Automatic, "MathFont" -> None, "LightDark" -> Automatic, "UseCache" -> True}

(* spec is an *optional* second argument (default Automatic). Do not split this
   into a separate 1-argument form that forwards to the 3-argument one: an empty
   OptionsPattern[] also matches Automatic, so MarkdownToNotebook[file, Automatic]
   matches both forms and, once the resource scraper reorders the down-values,
   forwards to itself without end (RecursionLimit). One definition with an optional
   spec avoids the ambiguity. *)
MarkdownToNotebook[file_String, spec : (_String | Automatic) : Automatic, opts : OptionsPattern[]] := Block[{
    (* Start the nesting counter self-contained: read $convertDepth only when it is
       already an integer, else treat it as 0. The load-time `$convertDepth = 0`
       (above) sets it in a Get-ed session, but a deployed ResourceFunction runs in a
       fresh kernel where that init may not have executed - and `$convertDepth + 1`
       on an *unbound* symbol binds the local to the symbolic `$convertDepth + 1`,
       which re-expands without end (RecursionLimit on every call). *)
    $convertDepth = If[IntegerQ[$convertDepth], $convertDepth, 0] + 1,
    evalExamples = TrueQ[OptionValue["Evaluate"]],
    useCache = TrueQ[OptionValue["UseCache"]],
    preserveSource = TrueQ[OptionValue["PreserveSource"]],
    evalSeparator = OptionValue["EvaluateSeparator"],
    (* "LightDark" -> "Dark" | "Light" pins the appearance the evaluated
       outputs (and the markdown twin's rasterizations) are rendered in;
       Automatic keeps the ambient $lightDark (the load-time default is
       "Light"). Block-local so nested conversions restore it. *)
    $lightDark = Replace[OptionValue["LightDark"],
        Automatic :> If[StringQ[$lightDark], $lightDark, "Light"]],
    src, text, parsed, meta, blocks, sections, tmplName, defCode, ctx, ctxPath,
    orderedCode, hashes, cacheDocName, cacheNames, cached, allHit, outputs, data, filled
},
    ensureParser[];
    src = resolveSource[file];
    text = src["Text"];
    parsed = litParse[text];
    meta = parsed["Metadata"];
    $docName = Lookup[meta, "Name", ""];
    $docPaclet = Lookup[meta, "Paclet", ""];
    $docContext = Lookup[meta, "Context", ""];
    blocks = resolveIncludes[parsed["Blocks"], src["Base"]];
    tmplName = Lookup[meta, "Template", "Default"];
    $docTemplate = tmplName;
    (* None (default) / "" / Automatic keep the front end's native math font -
       deterministic across machines and correctly sized inline; a family name
       (e.g. "Latin Modern Math") forces the Computer-Modern look. See applyMathFont. *)
    $mathFontFamily = OptionValue["MathFont"];

    (* evaluate every executable cell in document order, threading state in a
       private context (so the document's own code can't clobber the live
       session), cached by a cumulative hash of all cells up to each one.
       "---" thematic breaks and headings (at any level) are picked up
       alongside the executable cells so the evaluator can reset the context
       + cumulative-hash chain at each boundary (see resetBoundaryQ /
       cumulativeHashes / accumEval). *)
    (* recurse into Div blocks so executable cells nested inside ::: fenced
       divs (exercises, solutions, solved-examples, ...) get evaluated and
       cached alongside the top-level cells. *)
    orderedCode = Cases[blocks,
        b_ /; (executableQ[b] || MatchQ[b["Type"], "Separator" | "Heading"]), Infinity];
    hashes = cumulativeHashes[evalSeparator, orderedCode];
    (* build a per-cell PersistentObject name keyed by (DocName, cellIndex, hash).
       The doc name comes from the frontmatter Name when present (e.g.
       "Wolfram/MyPaclet") and falls back to the source's file basename;
       cellIndex is 1-based in evaluation order; the hash preserves
       content-addressing.  See exampleCacheName for the layout. *)
    cacheDocName = If[$docName === "", src["Name"], $docName];
    cacheNames = MapIndexed[exampleCacheName[cacheDocName, First[#2], #1] &, hashes];
    ctx = "MTNB$" <> IntegerString[Hash[text], 36] <> "`";
    (* let example cells resolve the documented paclet's symbols unqualified.
       NOT Context[MarkdownToNotebook]: that exposes every internal helper
       and Block local as a public symbol the example code can collide with
       (see issue #5 - a free `s` in an example would resolve to accumEval's
       Block-local `s` and bind to the per-cell state association). For
       self-referential examples (a doc whose example calls
       MarkdownToNotebook itself) we install a one-symbol forwarding alias
       in the per-doc context below. *)
    (* A page whose examples span more than its primary Context can name the
       extra contexts in a "ContextPath" frontmatter list; they join the
       evaluation $ContextPath so symbols from them resolve - and render -
       unqualified. Backward-compatible: absent -> {}. The paclet's primary context
       is included too, so a subpackage page (Context a subcontext of it) evaluates
       against the main-context symbols its subpackage imports. *)
    ctxPath = DeleteDuplicates @ Flatten @ {
        Lookup[meta, "Context", Nothing], Lookup[meta, "ContextPath", {}],
        docPacletContext[] /. "" -> Nothing, "System`"};
    installSelfAlias[ctx];
    (* "UseCache" -> False ignores the persistent cache's CONTENTS: every example
       re-evaluates and the fresh outputs are written back (below), refreshing the
       cache to match the current environment. The cache key is the cell's code
       hash with NO library version, so when the documented library changes but the
       example code does not, a warm cache would otherwise serve stale outputs;
       this is the knob to regenerate them (the standard alternative is to
       DeleteObject the PersistentObjects by hand). *)
    cached = If[useCache, AssociationThread[hashes -> Map[exampleCacheGet, cacheNames]], <||>];
    allHit = useCache && hashes =!= {} && AllTrue[cached, ! MissingQ[#] &];
    (* "Evaluate" -> False leaves the example cells unevaluated (input only). An
       example may itself convert another document (so its screenshot shows that
       document's own evaluated cells), which is one level of nesting; beyond that a
       hard depth cap stops a self-referential document - one whose example converts
       its own source - from recursing without end (the self-referential example
       passes "Evaluate" -> False to stop at the first level). *)
    outputs = Which[
        ! evalExamples || $convertDepth > 2, <||>,
        allHit, cached,
        True, evaluateAll[orderedCode, ctx, ctxPath, evalSeparator]
    ];
    (* Only persist CLEAN outputs - skip entries whose evaluation emitted kernel
       messages (Get::noopen, Needs::nocont, Failure[...], runtime errors, ...).
       Otherwise the very first build, before PacletDirectoryLoad or some other
       env setup is in place, poisons the cache with the failure messages and
       every subsequent build serves them back even after the env is fixed. *)
    If[ evalExamples && $convertDepth <= 2 && Not[allHit],
        MapThread[
            Function[{h, name},
                With[{entry = Lookup[outputs, h, Missing[]]},
                    If[ AssociationQ[entry] && Lookup[entry, "msgs", {}] === {},
                        exampleCacheSet[name, entry]
                    ]
                ]
            ],
            {hashes, cacheNames}
        ]
    ];

    blocks = annotateOutputs[blocks, hashes, outputs];
    sections = sectionsFrom[blocks];
    defCode = StringRiffle[#["Code"] & /@ sectionCells[sections, "definition"], "\n\n"];
    data = <|"meta" -> meta, "blocks" -> blocks, "sections" -> sections, "defCode" -> defCode|>;
    filled = applyDocFlag[buildNotebook[tmplName, data], Lookup[meta, "Flag", ""]];
    If[preserveSource, filled = withMarkdownSource[filled, text, tmplName]];
    (* assign deterministic CellIDs / ExpressionUUIDs last, so it also covers any
       cell added by withMarkdownSource *)
    filled = withDeterministicIDs[filled];

    Which[
        spec === Automatic || spec === "Notebook", filled,
        spec === "Association",
            <|"Notebook" -> filled, "Metadata" -> meta, "Sections" -> Keys[sections], "Template" -> tmplName|>,
        StringQ[spec] && StringEndsQ[ToLowerCase[spec], ".md"], markdownWithImages[blocks, meta, spec],
        True, exportDeterministicNB[spec, filled]
    ]
]