diff --git a/php-transformer/src/HtmlToBlocks/Elements/CustomWrapperConventions.php b/php-transformer/src/HtmlToBlocks/Elements/CustomWrapperConventions.php
new file mode 100644
index 000000000..6db5d658b
--- /dev/null
+++ b/php-transformer/src/HtmlToBlocks/Elements/CustomWrapperConventions.php
@@ -0,0 +1,163 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\Elements;
+
+use Automattic\BlocksEngine\PhpTransformer\Css\CssValueSplitter;
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\Style\StyleResolver;
+use DOMElement;
+
+/**
+ * Recognizes custom element tags used as a wrapping convention rather than as
+ * component hosts, and the author attribute selectors that still address an
+ * instance.
+ */
+final class CustomWrapperConventions
+{
+    /**
+     * Instances a custom element tag must reach before recurring usage can be
+     * read as a wrapping convention rather than a component.
+     */
+    private const WRAPPER_CONVENTION_MIN_INSTANCES = 3;
+
+    /**
+     * Depth of the shallow tag skeleton compared across wrapper instances.
+     */
+    private const WRAPPER_CONTENT_SHAPE_DEPTH = 2;
+
+    public function __construct(
+        private readonly StyleResolver $styleResolver
+    ) {
+    }
+
+    /**
+     * Data-attribute compounds written in author selectors, e.g. the
+     * `[data-key="a"]` of `[data-key="a"] .photo`.
+     *
+     * @return array<string, true>
+     */
+    public function authorDataAttributeSelectors(string $css): array
+    {
+        $selectors = array();
+        foreach ( CssValueSplitter::ruleBlocks($css) as $rule ) {
+            if ( ! str_contains($rule['selector'], '[data-') ) {
+                continue;
+            }
+            if ( preg_match_all('/\[\s*data-[A-Za-z][A-Za-z0-9_-]*\s*(?:[*^$|~]?=\s*(?:"(?:\\\\.|[^"\\\\])*"|\'(?:\\\\.|[^\'\\\\])*\'|[^\]\s"\']+)\s*(?:[is]\s*)?)?\]/', $rule['selector'], $matches) ) {
+                foreach ( $matches[0] as $selector ) {
+                    $selectors[$selector] = true;
+                }
+            }
+        }
+
+        return $selectors;
+    }
+
+    /**
+     * Whether an author selector keys on this instance through its own
+     * attributes. Such an instance is a selector hook, not a wrapping
+     * convention: removing it silently detaches every rule that needs it as
+     * a subject or ancestor. Equality compounds must match the instance's
+     * value; any other operator fails closed on the attribute name.
+     *
+     * @param array<string, true> $selectors
+     */
+    public function authorAttributeSelectorAddresses(DOMElement $element, array $selectors): bool
+    {
+        foreach ( array_keys($selectors) as $selector ) {
+            $parsed = \Automattic\BlocksEngine\PhpTransformer\Support\RuntimeSelectorVocabulary::parseAttributeSelector($selector);
+            if ( null !== $parsed ) {
+                if ( \Automattic\BlocksEngine\PhpTransformer\Support\RuntimeSelectorVocabulary::matchesElement($element, $selector, array()) ) {
+                    return true;
+                }
+                continue;
+            }
+            if ( 1 === preg_match('/^\[\s*(data-[A-Za-z][A-Za-z0-9_-]*)/', $selector, $name) && $element->hasAttribute(strtolower($name[1])) ) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Whether a custom element tag is used as a wrapping convention rather than
+     * as a component host.
+     *
+     * @param array<int, DOMElement> $elements Every instance of the tag.
+     */
+    public function isWrapperConventionTag(string $tag, array $elements, string $staticCss): bool
+    {
+        if ( self::WRAPPER_CONVENTION_MIN_INSTANCES > count($elements) ) {
+            return false;
+        }
+
+        // A tag that carries presentation of its own is not render-neutral.
+        // `display:contents` is the exception that proves the rule: it states
+        // the element generates no box and renders as its children.
+        if ( ! $this->customElementCssIsRenderNeutral($tag, $staticCss) ) {
+            return false;
+        }
+
+        $shapes = array();
+        foreach ( $elements as $element ) {
+            $shapes[$this->wrappedContentShape($element)] = true;
+            if ( 1 < count($shapes) ) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Whether every author rule addressing a custom element tag leaves it
+     * render-neutral, so replacing instances with their children preserves the
+     * authored presentation.
+     */
+    private function customElementCssIsRenderNeutral(string $tag, string $css): bool
+    {
+        if ( '' === trim($css) ) {
+            return true;
+        }
+
+        $pattern = '/(?<![\w-])' . preg_quote($tag, '/') . '(?![\w-])/i';
+        if ( 1 !== preg_match($pattern, $css) ) {
+            return true;
+        }
+
+        foreach ( CssValueSplitter::ruleBlocks($css) as $rule ) {
+            if ( 1 !== preg_match($pattern, $rule['selector']) ) {
+                continue;
+            }
+            foreach ( $this->styleResolver->cssDeclarations($rule['declarations']) as $property => $value ) {
+                if ( 'display' !== strtolower(trim($property)) || 'contents' !== strtolower(trim($value)) ) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Shallow tag skeleton of the content a wrapper carries. Instances of a real
+     * component repeat this shape; instances of a wrapper do not.
+     */
+    private function wrappedContentShape(DOMElement $element, int $depth = 0): string
+    {
+        $parts = array();
+        foreach ( $element->childNodes as $child ) {
+            if ( ! $child instanceof DOMElement ) {
+                continue;
+            }
+            $tag = strtolower($child->tagName);
+            $parts[] = self::WRAPPER_CONTENT_SHAPE_DEPTH > $depth
+                ? $tag . '(' . $this->wrappedContentShape($child, $depth + 1) . ')'
+                : $tag;
+        }
+
+        return implode(',', $parts);
+    }
+}
diff --git a/php-transformer/src/HtmlToBlocks/HtmlCompilation.php b/php-transformer/src/HtmlToBlocks/HtmlCompilation.php
index 25f009824..58fd85f78 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlCompilation.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlCompilation.php
@@ -209,16 +209,6 @@ final class HtmlCompilation extends SourceBlockCreator implements RichTextInline
 {
     private const GENERATED_COMPONENT_MIN_SOURCE_DEPTH = 14;
 
-    /**
-     * Instances a custom element tag must reach before recurring usage can be
-     * read as a wrapping convention rather than a component.
-     */
-    private const WRAPPER_CONVENTION_MIN_INSTANCES = 3;
-
-    /**
-     * Depth of the shallow tag skeleton compared across wrapper instances.
-     */
-    private const WRAPPER_CONTENT_SHAPE_DEPTH = 2;
     use DomHelpersTrait;
 
     private readonly AuthorLayoutOwnership $authorLayoutOwnership;
@@ -317,6 +307,7 @@ final class HtmlCompilation extends SourceBlockCreator implements RichTextInline
     private readonly Elements\RenderNeutralElements $renderNeutral;
     private readonly Elements\InertElements $inertElements;
     private readonly Elements\EmptyInlineGeometryLowering $emptyInlineGeometry;
+    private readonly Elements\CustomWrapperConventions $wrapperConventions;
     private readonly SourceProvenance $sourceProvenance;
 
     private readonly RuntimeResourceElementConverter $runtimeResourceConverter;
@@ -611,6 +602,7 @@ function (DOMElement $element): array {
         $this->renderNeutral = new Elements\RenderNeutralElements($this->session, $this->styleResolver, $this->sourceElementClassifier, $this->sourceElementDescription, $this->runtimeIslands, $this->emptyElementFootprint);
         $this->inertElements = new Elements\InertElements($this->styleResolver, $this->sourceElementClassifier, $this->sourceVisibility, $this->runtimeIslands);
         $this->emptyInlineGeometry = new Elements\EmptyInlineGeometryLowering($this, $this->session, $this->sourceElementClassifier, $this->emptyElementFootprint, $this->authoredStateButtons, $this->layoutShells, $this->runtimeIslands);
+        $this->wrapperConventions = new Elements\CustomWrapperConventions($this->styleResolver);
         $this->customImageHosts = new Elements\CustomImageHostLowering($this, $this->blockFactory, $this->styleResolver, $this->session, $this->sourceElementClassifier, $this->sourceElementDescription, $this->imageLowering, $this->layoutShells, $this->runtimeIslands, $this->authorLayoutOwnership);
         $this->anchors = new Elements\AnchorLowering($this, $this, $this->styleResolver, $this->session, $this->sourceElementClassifier, $this->sourceElementDescription, $this->imageLowering, $this->imageUrls, $this->layoutShells, $this->linkWrapperPropagator, $this->runtimeIslands, $this->customImageHosts);
         $this->layoutTables = new Elements\LayoutTableLowering(
@@ -2265,13 +2257,13 @@ private function unwrapRenderNeutralCustomElements(DOMElement $body, string $sta
 
         $attributeSelectors = null;
         foreach ( $instances as $tag => $elements ) {
-            if ( ! $this->isWrapperConventionTag($tag, $elements, $staticCss) ) {
+            if ( ! $this->wrapperConventions->isWrapperConventionTag($tag, $elements, $staticCss) ) {
                 continue;
             }
-            $attributeSelectors ??= $this->authorDataAttributeSelectors($staticCss);
+            $attributeSelectors ??= $this->wrapperConventions->authorDataAttributeSelectors($staticCss);
             foreach ( $elements as $element ) {
                 if ( $this->renderNeutral->isRenderNeutralWrapper($element, false) ) {
-                    if ( $this->authorAttributeSelectorAddresses($element, $attributeSelectors) ) {
+                    if ( $this->wrapperConventions->authorAttributeSelectorAddresses($element, $attributeSelectors) ) {
                         $this->retainedCustomWrapperHooks[] = $element;
                     } else {
                         $this->richTextStylingHooks()->unwrapElement($element);
@@ -2281,86 +2273,6 @@ private function unwrapRenderNeutralCustomElements(DOMElement $body, string $sta
         }
     }
 
-    /**
-     * Data-attribute compounds written in author selectors, e.g. the
-     * `[data-key="a"]` of `[data-key="a"] .photo`.
-     *
-     * @return array<string, true>
-     */
-    private function authorDataAttributeSelectors(string $css): array
-    {
-        $selectors = array();
-        foreach ( CssValueSplitter::ruleBlocks($css) as $rule ) {
-            if ( ! str_contains($rule['selector'], '[data-') ) {
-                continue;
-            }
-            if ( preg_match_all('/\[\s*data-[A-Za-z][A-Za-z0-9_-]*\s*(?:[*^$|~]?=\s*(?:"(?:\\\\.|[^"\\\\])*"|\'(?:\\\\.|[^\'\\\\])*\'|[^\]\s"\']+)\s*(?:[is]\s*)?)?\]/', $rule['selector'], $matches) ) {
-                foreach ( $matches[0] as $selector ) {
-                    $selectors[$selector] = true;
-                }
-            }
-        }
-
-        return $selectors;
-    }
-
-    /**
-     * Whether an author selector keys on this instance through its own
-     * attributes. Such an instance is a selector hook, not a wrapping
-     * convention: removing it silently detaches every rule that needs it as
-     * a subject or ancestor. Equality compounds must match the instance's
-     * value; any other operator fails closed on the attribute name.
-     *
-     * @param array<string, true> $selectors
-     */
-    private function authorAttributeSelectorAddresses(DOMElement $element, array $selectors): bool
-    {
-        foreach ( array_keys($selectors) as $selector ) {
-            $parsed = \Automattic\BlocksEngine\PhpTransformer\Support\RuntimeSelectorVocabulary::parseAttributeSelector($selector);
-            if ( null !== $parsed ) {
-                if ( \Automattic\BlocksEngine\PhpTransformer\Support\RuntimeSelectorVocabulary::matchesElement($element, $selector, array()) ) {
-                    return true;
-                }
-                continue;
-            }
-            if ( 1 === preg_match('/^\[\s*(data-[A-Za-z][A-Za-z0-9_-]*)/', $selector, $name) && $element->hasAttribute(strtolower($name[1])) ) {
-                return true;
-            }
-        }
-
-        return false;
-    }
-
-    /**
-     * Whether a custom element tag is used as a wrapping convention rather than
-     * as a component host.
-     *
-     * @param array<int, DOMElement> $elements Every instance of the tag.
-     */
-    private function isWrapperConventionTag(string $tag, array $elements, string $staticCss): bool
-    {
-        if ( self::WRAPPER_CONVENTION_MIN_INSTANCES > count($elements) ) {
-            return false;
-        }
-
-        // A tag that carries presentation of its own is not render-neutral.
-        // `display:contents` is the exception that proves the rule: it states
-        // the element generates no box and renders as its children.
-        if ( ! $this->customElementCssIsRenderNeutral($tag, $staticCss) ) {
-            return false;
-        }
-
-        $shapes = array();
-        foreach ( $elements as $element ) {
-            $shapes[$this->wrappedContentShape($element)] = true;
-            if ( 1 < count($shapes) ) {
-                return true;
-            }
-        }
-
-        return false;
-    }
-
     /**
      * Author CSS visible to the document: declared stylesheets plus the styles
      * the source embeds inline.
@@ -2370,56 +2282,6 @@ private function authoredCssText(string $html, string $staticCss): string
         return $this->stylesheetAnalysisComposer->combinedAuthorStylesheet($html, $staticCss);
     }
 
-    /**
-     * Whether every author rule addressing a custom element tag leaves it
-     * render-neutral, so replacing instances with their children preserves the
-     * authored presentation.
-     */
-    private function customElementCssIsRenderNeutral(string $tag, string $css): bool
-    {
-        if ( '' === trim($css) ) {
-            return true;
-        }
-
-        $pattern = '/(?<![\w-])' . preg_quote($tag, '/') . '(?![\w-])/i';
-        if ( 1 !== preg_match($pattern, $css) ) {
-            return true;
-        }
-
-        foreach ( CssValueSplitter::ruleBlocks($css) as $rule ) {
-            if ( 1 !== preg_match($pattern, $rule['selector']) ) {
-                continue;
-            }
-            foreach ( $this->styleResolver->cssDeclarations($rule['declarations']) as $property => $value ) {
-                if ( 'display' !== strtolower(trim($property)) || 'contents' !== strtolower(trim($value)) ) {
-                    return false;
-                }
-            }
-        }
-
-        return true;
-    }
-
-    /**
-     * Shallow tag skeleton of the content a wrapper carries. Instances of a real
-     * component repeat this shape; instances of a wrapper do not.
-     */
-    private function wrappedContentShape(DOMElement $element, int $depth = 0): string
-    {
-        $parts = array();
-        foreach ( $element->childNodes as $child ) {
-            if ( ! $child instanceof DOMElement ) {
-                continue;
-            }
-            $tag = strtolower($child->tagName);
-            $parts[] = self::WRAPPER_CONTENT_SHAPE_DEPTH > $depth
-                ? $tag . '(' . $this->wrappedContentShape($child, $depth + 1) . ')'
-                : $tag;
-        }
-
-        return implode(',', $parts);
-    }
-
     private function collectGeneratedComponentCandidates(DOMElement $element, int $depth = 0): void
     {
         if (self::GENERATED_COMPONENT_MIN_SOURCE_DEPTH <= $depth