diff --git a/docs/internals/escaping.md b/docs/internals/escaping.md
index 25802a9f0..6b2f2bb32 100644
--- a/docs/internals/escaping.md
+++ b/docs/internals/escaping.md
@@ -12,9 +12,9 @@ layers that must stay in sync**.
   `(contentType, state, subType)`, emits a string that **calls** a runtime escaping
   function (e.g. `LR\HtmlHelpers::escapeText(...)`, `LR\Helpers::escapeCss(...)`;
   plain-text output goes through the `escape` filter instead). The subType is not
-  purely state-derived: `enterHtmlAttribute` infers `js` for `on*` and `css` for
-  `style` attributes, and `enterHtmlText` classifies a `<script>` by its `type`
-  attribute. `export()` serializes the state as a composite string
+  purely state-derived: `enterHtmlAttribute` infers `js` for `on*`, `css` for
+  `style` and `html` for `srcdoc` attributes, and `enterHtmlText` classifies a
+  `<script>` by its `type` attribute. `export()` serializes the state as a composite string
   (`'html/attr/js'`) — the key format used for block escaping and the convertor
   table below.
 - **Runtime** — the actual escaping functions live in `Runtime\Helpers` (JS / CSS /
@@ -36,6 +36,23 @@ type or a changed escaping rule must be reflected in *both* `Compiler\Escaper` a
 `Runtime\*` helpers, or generated templates will call an escaper that behaves
 differently than the compiler assumed.
 
+## `srcdoc` is escaped twice
+
+The value of `srcdoc` is an HTML document: the browser attribute-decodes it and then
+parses the result as HTML. Escaping it only as an attribute is therefore an XSS —
+`&lt;script&gt;` decodes to a live `<script>`, and an iframe without `sandbox` shares
+the parent's origin. `HtmlHelpers::escapeHtmlAttr` escapes a value as HTML text first
+and as an attribute second; an `Html` object passes through `escapeText` as markup
+and is encoded only once, so trusted HTML keeps its tags. All three places route
+`srcdoc` through it: the `html/attr/html` state in `escape()` and in the
+`Convertors`, and `formatSrcdocAttribute` for dynamic attributes and `n:attr`.
+
+With `Feature::MigrationWarnings`, `formatSrcdocAttribute` warns about a plain value
+whose document differs from its text (it contains `<` or a character reference),
+i.e. one that used to render as markup. Only the formatter paths warn: a mixed value
+like `srcdoc="<p>{$x}</p>"` is escaped by code `Escaper::escape()` emits, and
+`Escaper` has no access to feature flags.
+
 ## How nodes obtain the context: the `PrintContext` escaper stack
 
 At print time the current escaping context lives in a **stack of `Escaper`s inside
@@ -54,7 +71,7 @@ element's `restoreEscape()` and leak the context past the element.
 A whole HTML attribute generated from an expression (`Html\ExpressionAttributeNode`)
 is not escaped via `Escaper` at all. The node picks a
 `Runtime\HtmlHelpers::format*Attribute` method at compile time — the attribute *type*
-(`bool`/`tristate`/`valuedBool`/`list`/`data`/`aria`/`style`) comes from the attribute name via
+(`bool`/`tristate`/`valuedBool`/`list`/`data`/`aria`/`style`/`srcdoc`) comes from the attribute name via
 `classifyAttributeType`, or is forced by an attribute modifier: `|toggle` anywhere in
 the chain, `|json` only as the **last** modifier (`json` never comes from the
 attribute name). Any non-HTML content type falls back to
diff --git a/src/Latte/Compiler/Escaper.php b/src/Latte/Compiler/Escaper.php
index 925c912e5..dc75decd9 100644
--- a/src/Latte/Compiler/Escaper.php
+++ b/src/Latte/Compiler/Escaper.php
@@ -40,6 +40,7 @@ class Escaper
 			self::HtmlAttribute => 'HtmlHelpers::escapeAttr',
 			self::HtmlAttribute . '/' . self::JavaScript => 'HtmlHelpers::escapeAttr',
 			self::HtmlAttribute . '/' . self::Css => 'HtmlHelpers::escapeAttr',
+			self::HtmlAttribute . '/' . self::HtmlText => 'HtmlHelpers::escapeHtmlAttr',
 			self::HtmlComment => 'HtmlHelpers::escapeComment',
 			'xml' => 'XmlHelpers::escapeText',
 			'xml/attr' => 'XmlHelpers::escapeAttr',
@@ -48,6 +49,7 @@ class Escaper
 			self::HtmlText => 'HtmlHelpers::escapeText',
 			self::HtmlAttribute => 'HtmlHelpers::escapeAttr',
 			self::HtmlAttribute . '/' . self::JavaScript => 'HtmlHelpers::escapeAttr',
+			self::HtmlAttribute . '/' . self::HtmlText => 'HtmlHelpers::escapeHtmlAttr',
 			self::HtmlRawText . '/' . self::JavaScript => 'HtmlHelpers::convertJSToRawText',
 			self::HtmlComment => 'HtmlHelpers::escapeComment',
 		],
@@ -55,6 +57,7 @@ class Escaper
 			self::HtmlText => 'HtmlHelpers::escapeText',
 			self::HtmlAttribute => 'HtmlHelpers::escapeAttr',
 			self::HtmlAttribute . '/' . self::Css => 'HtmlHelpers::escapeAttr',
+			self::HtmlAttribute . '/' . self::HtmlText => 'HtmlHelpers::escapeHtmlAttr',
 			self::HtmlRawText . '/' . self::Css => 'HtmlHelpers::convertJSToRawText',
 			self::HtmlComment => 'HtmlHelpers::escapeComment',
 		],
@@ -63,6 +66,7 @@ class Escaper
 			self::HtmlAttribute => 'HtmlHelpers::convertHtmlToAttr',
 			self::HtmlAttribute . '/' . self::JavaScript => 'HtmlHelpers::convertHtmlToAttr',
 			self::HtmlAttribute . '/' . self::Css => 'HtmlHelpers::convertHtmlToAttr',
+			self::HtmlAttribute . '/' . self::HtmlText => 'HtmlHelpers::escapeAttr',
 			self::HtmlComment => 'HtmlHelpers::escapeComment',
 			self::HtmlRawText . '/' . self::HtmlText => 'HtmlHelpers::convertHtmlToRawText',
 		],
@@ -155,6 +159,8 @@ public function enterHtmlAttribute(?string $name = null): void
 				$this->subType = self::JavaScript;
 			} elseif ($name === 'style') {
 				$this->subType = self::Css;
+			} elseif ($name === 'srcdoc') {
+				$this->subType = self::HtmlText;
 			}
 		}
 	}
@@ -182,6 +188,7 @@ public function escape(string $str): string
 					'' => 'LR\HtmlHelpers::escapeAttr(' . $str . ')',
 					self::JavaScript => 'LR\HtmlHelpers::escapeAttr(LR\Helpers::escapeJs(' . $str . '))',
 					self::Css => 'LR\HtmlHelpers::escapeAttr(LR\Helpers::escapeCss(' . $str . '))',
+					self::HtmlText => 'LR\HtmlHelpers::escapeHtmlAttr(' . $str . ')',
 				},
 				self::HtmlComment => 'LR\HtmlHelpers::escapeComment(' . $str . ')',
 				self::HtmlBogusTag => 'LR\HtmlHelpers::escapeTag(' . $str . ')',
diff --git a/src/Latte/Runtime/HtmlHelpers.php b/src/Latte/Runtime/HtmlHelpers.php
index 94d57186f..197b71de6 100644
--- a/src/Latte/Runtime/HtmlHelpers.php
+++ b/src/Latte/Runtime/HtmlHelpers.php
@@ -72,6 +72,15 @@ public static function escapeAttr(mixed $s): string
 	}
 
 
+	/**
+	 * Escapes HTML for use inside attribute holding an HTML document (srcdoc).
+	 */
+	public static function escapeHtmlAttr(mixed $s): string
+	{
+		return self::escapeAttr(self::escapeText($s));
+	}
+
+
 	/**
 	 * Escapes string for use inside HTML tag.
 	 */
@@ -175,7 +184,7 @@ public static function convertHtmlToText(string $s): string
 
 
 	/**
-	 * Returns the type category of an HTML attribute: 'bool', 'tristate', 'valuedBool', 'list', 'data', 'aria', 'style', or ''.
+	 * Returns the type category of an HTML attribute: 'bool', 'tristate', 'valuedBool', 'list', 'data', 'aria', 'style', 'srcdoc', or ''.
 	 */
 	public static function classifyAttributeType(string $name): string
 	{
@@ -188,6 +197,7 @@ public static function classifyAttributeType(string $name): string
 			str_starts_with($name, 'data-') => 'data',
 			str_starts_with($name, 'aria-') => 'aria',
 			$name === 'style' => 'style',
+			$name === 'srcdoc' => 'srcdoc',
 			default => '',
 		};
 	}
@@ -274,6 +284,26 @@ public static function formatStyleAttribute(string $namePart, mixed $value): str
 	}
 
 
+	/**
+	 * Formats HTML attribute 'srcdoc', whose value is an HTML document.
+	 */
+	public static function formatSrcdocAttribute(string $namePart, mixed $value, bool $migrationWarnings = false): string
+	{
+		if (!is_string($value) && !is_int($value) && !is_float($value) && !$value instanceof \Stringable) {
+			return self::formatAttribute($namePart, $value, $migrationWarnings);
+		}
+
+		if ($migrationWarnings
+			&& !$value instanceof HtmlStringable
+			&& !$value instanceof Nette\HtmlStringable
+			&& (str_contains($s = (string) $value, '<') || html_entity_decode($s, ENT_QUOTES | ENT_HTML5, 'UTF-8') !== $s) // the document differs from the text
+		) {
+			self::triggerMigrationWarning(trim($namePart), 'string value: previously it was rendered as HTML, now it is escaped as text (wrap trusted HTML in Latte\Runtime\Html)');
+		}
+		return $namePart . '="' . self::escapeHtmlAttr($value) . '"';
+	}
+
+
 	/**
 	 * Formats data-* HTML attribute.
 	 */
diff --git a/tests/common/Engine.migrationWarnings.phpt b/tests/common/Engine.migrationWarnings.phpt
index 28b096480..109806868 100644
--- a/tests/common/Engine.migrationWarnings.phpt
+++ b/tests/common/Engine.migrationWarnings.phpt
@@ -39,6 +39,12 @@ Assert::error(
 	'Behavior change for attribute \'contenteditable\' with value false: previously it rendered as contenteditable="", now it renders as contenteditable="false" (on line 1 at column 25)',
 );
 
+Assert::error(
+	fn() => $latte->renderToString('<iframe srcdoc="{=\'<b>x</b>\'}">'),
+	E_USER_WARNING,
+	'Behavior change for attribute \'srcdoc\' with string value: previously it was rendered as HTML, now it is escaped as text (wrap trusted HTML in Latte\Runtime\Html) (on line 1 at column 19)',
+);
+
 // |accept
 Assert::same(
 	'<input>',
diff --git a/tests/common/contentType.html.srcdoc.phpt b/tests/common/contentType.html.srcdoc.phpt
new file mode 100644
index 000000000..72d84cd97
--- /dev/null
+++ b/tests/common/contentType.html.srcdoc.phpt
@@ -0,0 +1,97 @@
+<?php declare(strict_types=1);
+
+/**
+ * Test: HTML document in srcdoc attribute
+ */
+
+use Latte\Runtime\Html;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+$latte = createLatte();
+$params = [
+	'x' => '<script>alert("1")</script> & {',
+	'html' => new Html('<b title="a&amp;b">bold</b>'),
+];
+
+// text is escaped for HTML and then for the attribute
+Assert::same(
+	'<iframe srcdoc="<p>&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;</p>"></iframe>',
+	$latte->renderToString('<iframe srcdoc="<p>{$x}</p>"></iframe>', $params),
+);
+
+Assert::same(
+	'<iframe srcdoc="&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;"></iframe>',
+	$latte->renderToString("<iframe srcdoc='{\$x}'></iframe>", $params),
+);
+
+Assert::same(
+	'<iframe SRCDOC="a&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;"></iframe>',
+	$latte->renderToString('<iframe SRCDOC=a{$x}></iframe>', $params),
+);
+
+// HTML is escaped only for the attribute
+Assert::same(
+	'<iframe srcdoc="&lt;b title=&quot;a&amp;amp;b&quot;&gt;bold&lt;/b&gt;"></iframe>',
+	$latte->renderToString('<iframe srcdoc="{$html}"></iframe>', $params),
+);
+
+// |noescape escapes only quotes
+Assert::same(
+	'<iframe srcdoc="<script>alert(&quot;1&quot;)</script> & {"></iframe>',
+	$latte->renderToString('<iframe srcdoc="{$x|noescape}"></iframe>', $params),
+);
+
+// dynamic attribute
+Assert::same(
+	'<iframe srcdoc="&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;"></iframe>',
+	$latte->renderToString('<iframe srcdoc={$x}></iframe>', $params),
+);
+
+Assert::same(
+	'<iframe srcdoc="&lt;b title=&quot;a&amp;amp;b&quot;&gt;bold&lt;/b&gt;"></iframe>',
+	$latte->renderToString('<iframe srcdoc={$html}></iframe>', $params),
+);
+
+Assert::same(
+	'<iframe></iframe>',
+	$latte->renderToString('<iframe srcdoc={$none}></iframe>', ['none' => null]),
+);
+
+// n:attr
+Assert::same(
+	'<iframe srcdoc="&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;"></iframe>',
+	$latte->renderToString('<iframe n:attr="srcdoc => $x"></iframe>', $params),
+);
+
+Assert::same(
+	'<iframe srcdoc="&lt;b title=&quot;a&amp;amp;b&quot;&gt;bold&lt;/b&gt;"></iframe>',
+	$latte->renderToString('<iframe n:attr="srcdoc => $html"></iframe>', $params),
+);
+
+// blocks
+Assert::same(
+	'<iframe srcdoc="&lt;i&gt;&amp;lt;script&amp;gt;alert(&quot;1&quot;)&amp;lt;/script&amp;gt; &amp;amp; &amp;#123;&lt;/i&gt;"></iframe>',
+	$latte->renderToString('{define doc}<i>{$x}</i>{/define}<iframe srcdoc="{include doc}"></iframe>', $params),
+);
+
+$latte->setLoader(new Latte\Loaders\StringLoader([
+	'main' => '<iframe srcdoc="{include html.latte}"></iframe> <iframe srcdoc="{include text.latte}"></iframe> <iframe srcdoc="{include js.latte}"></iframe>',
+	'html.latte' => '<i> &amp; </i>',
+	'text.latte' => '{contentType text}<i> & "',
+	'js.latte' => '{contentType javascript}a < b',
+]));
+
+Assert::same(
+	'<iframe srcdoc="&lt;i&gt; &amp;amp; &lt;/i&gt;"></iframe> <iframe srcdoc="&amp;lt;i&amp;gt; &amp;amp; &quot;"></iframe> <iframe srcdoc="a &amp;lt; b"></iframe>',
+	$latte->renderToString('main'),
+);
+
+// XML has no srcdoc context
+$latte->setLoader(new Latte\Loaders\StringLoader);
+Assert::same(
+	'<iframe srcdoc="&lt;p&gt;&lt;script&gt;alert(&quot;1&quot;)&lt;/script&gt; &amp; {&lt;/p&gt;"></iframe>',
+	$latte->renderToString('{contentType xml}<iframe srcdoc="{=\'<p>\'}{$x}{=\'</p>\'}"></iframe>', $params),
+);
diff --git a/tests/runtime/HtmlHelpers.escapeHtmlAttr.phpt b/tests/runtime/HtmlHelpers.escapeHtmlAttr.phpt
new file mode 100644
index 000000000..ac2569bdd
--- /dev/null
+++ b/tests/runtime/HtmlHelpers.escapeHtmlAttr.phpt
@@ -0,0 +1,17 @@
+<?php declare(strict_types=1);
+
+use Latte\Runtime\Html;
+use Latte\Runtime\HtmlHelpers;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+Assert::same('', HtmlHelpers::escapeHtmlAttr(null));
+Assert::same('', HtmlHelpers::escapeHtmlAttr(''));
+Assert::same('1', HtmlHelpers::escapeHtmlAttr(1));
+Assert::same('&amp;lt;b&amp;gt; &amp;amp; &quot; &apos;', HtmlHelpers::escapeHtmlAttr('<b> & " \''));
+Assert::same('&amp;#123; &#123;&lt;!-- --&gt;&#123;',HtmlHelpers::escapeHtmlAttr('{ {{'));
+Assert::same('&amp;amp;amp;', HtmlHelpers::escapeHtmlAttr('&amp;'));
+Assert::same('&lt;b title=&quot;x&quot;&gt;a &amp;amp; b&lt;/b&gt;', HtmlHelpers::escapeHtmlAttr(new Html('<b title="x">a &amp; b</b>')));
+Assert::same('&#123;', HtmlHelpers::escapeHtmlAttr(new Html('{')));
diff --git a/tests/runtime/HtmlHelpers.formatSrcdocAttribute.phpt b/tests/runtime/HtmlHelpers.formatSrcdocAttribute.phpt
new file mode 100644
index 000000000..ba1e44144
--- /dev/null
+++ b/tests/runtime/HtmlHelpers.formatSrcdocAttribute.phpt
@@ -0,0 +1,45 @@
+<?php declare(strict_types=1);
+
+use Latte\Runtime\Html;
+use Latte\Runtime\HtmlHelpers;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+class StringObject
+{
+	public function __toString()
+	{
+		return 'one&<br>';
+	}
+}
+
+
+Assert::same('srcdoc', HtmlHelpers::classifyAttributeType('srcdoc'));
+Assert::same('srcdoc', HtmlHelpers::classifyAttributeType('SrcDoc'));
+
+// escaped by escapeHtmlAttr
+Assert::same('srcdoc="&amp;lt;b&amp;gt;"', HtmlHelpers::formatSrcdocAttribute('srcdoc', '<b>'));
+Assert::same(' srcdoc="&lt;b&gt;"', HtmlHelpers::formatSrcdocAttribute(' srcdoc', new Html('<b>')));
+
+// migration warnings
+foreach (['<b>x</b>', 'a &amp; b', new StringObject] as $value) {
+	Assert::error(
+		fn() => HtmlHelpers::formatSrcdocAttribute('srcdoc', $value, migrationWarnings: true),
+		E_USER_WARNING,
+		"Behavior change for attribute 'srcdoc' with string value: previously it was rendered as HTML, now it is escaped as text (wrap trusted HTML in Latte\\Runtime\\Html).",
+	);
+}
+
+foreach (['a & b > " {', 1, new Html('<b>x</b>')] as $value) { // renders the same document as before
+	Assert::noError(fn() => HtmlHelpers::formatSrcdocAttribute('srcdoc', $value, migrationWarnings: true));
+}
+
+// null & invalid
+Assert::same('', HtmlHelpers::formatSrcdocAttribute('srcdoc', null));
+Assert::error(
+	fn() => Assert::same('', HtmlHelpers::formatSrcdocAttribute('srcdoc', [])),
+	E_USER_WARNING,
+	"Invalid value for attribute 'srcdoc': array is not allowed.",
+);