HTML API: Ignore slash inside unquoted attribute values

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -3337,7 +3337,34 @@ public function has_self_closing_flag(): bool {
 		 *     <figure />
 		 *             ^ this appears one character before the end of the closing ">".
 		 */
-		return '/' === $this->html[ $this->token_starts_at + $this->token_length - 2 ];
+		$self_closing_flag_at = $this->token_starts_at + $this->token_length - 2;
+		if ( '/' !== $this->html[ $self_closing_flag_at ] ) {
+			return false;
+		}
+
+		foreach ( $this->attributes as $attribute ) {
+			$attribute_ends_at = $attribute->start + $attribute->length;
+			if (
+				$self_closing_flag_at >= $attribute->start &&
+				$self_closing_flag_at < $attribute_ends_at
+			) {
+				return false;
+			}
+		}
+
+		foreach ( $this->duplicate_attributes ?? array() as $duplicate_attributes ) {
+			foreach ( $duplicate_attributes as $attribute ) {
+				$attribute_ends_at = $attribute->start + $attribute->length;
+				if (
+					$self_closing_flag_at >= $attribute->start &&
+					$self_closing_flag_at < $attribute_ends_at
+				) {
+					return false;
+				}
+			}
+		}
+
+		return true;
 	}
 
 	/**

tests/phpunit/tests/html-api/wpHtmlProcessor.php

@@ -583,6 +583,38 @@ public function test_expects_closer_foreign_content_self_closing() {
 		$this->assertTrue( $processor->expects_closer() );
 	}
 
+	/**
+	 * Ensures a trailing slash in an unquoted attribute value does not close foreign content.
+	 *
+	 * @ticket 61576
+	 */
+	public function test_trailing_slash_in_unquoted_attribute_value_does_not_self_close_foreign_content() {
+		$processor = WP_HTML_Processor::create_fragment( '<math><mi disabled=abc/>text</math>' );
+
+		$this->assertTrue( $processor->next_tag( 'MI' ), 'Could not find MI tag: check test setup.' );
+		$this->assertSame(
+			'abc/',
+			$processor->get_attribute( 'disabled' ),
+			'Trailing slash in unquoted attribute value should belong to the attribute value.'
+		);
+		$this->assertFalse(
+			$processor->has_self_closing_flag(),
+			'Trailing slash in unquoted attribute value should not be interpreted as a self-closing flag.'
+		);
+		$this->assertTrue(
+			$processor->expects_closer(),
+			'MI with a trailing slash in an unquoted attribute value should still expect a closer.'
+		);
+
+		$this->assertTrue( $processor->next_token(), 'Could not find text following MI tag: check test setup.' );
+		$this->assertSame( '#text', $processor->get_token_name(), 'Should have found the text node following the MI tag.' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'MATH', 'MI', '#text' ),
+			$processor->get_breadcrumbs(),
+			'Text following the MI tag should remain inside the MI element.'
+		);
+	}
+
 	/**
 	 * Ensures that expects_closer works for void-like elements in foreign content.
 	 *

tests/phpunit/tests/html-api/wpHtmlTagProcessor.php

@@ -111,13 +111,38 @@ public static function data_has_self_closing_flag() {
 			'No self-closing flag on a foreign element'  => array( '<circle>', false ),
 			// These involve syntax peculiarities.
 			'Self-closing flag after extra spaces'       => array( '<div      />', true ),
-			'Self-closing flag after attribute'          => array( '<div id=test/>', true ),
+			'Self-closing flag after attribute'          => array( '<div id=test />', true ),
+			'Slash inside unquoted attribute value'      => array( '<div id=test/>', false ),
 			'Self-closing flag after quoted attribute'   => array( '<div id="test"/>', true ),
 			'Self-closing flag after boolean attribute'  => array( '<div enabled/>', true ),
 			'Boolean attribute that looks like a self-closer' => array( '<div / >', false ),
 		);
 	}
 
+	/**
+	 * Ensures a trailing slash in an unquoted attribute value is part of the value.
+	 *
+	 * @ticket 61576
+	 *
+	 * @covers WP_HTML_Tag_Processor::get_attribute
+	 * @covers WP_HTML_Tag_Processor::has_self_closing_flag
+	 */
+	public function test_trailing_slash_in_unquoted_attribute_value_is_not_self_closing_flag() {
+		$processor = new WP_HTML_Tag_Processor( '<mi disabled=abc/>text' );
+		$this->assertTrue( $processor->next_tag(), 'Could not find MI tag: check test setup.' );
+
+		$this->assertSame(
+			'abc/',
+			$processor->get_attribute( 'disabled' ),
+			'Trailing slash in unquoted attribute value should belong to the attribute value.'
+		);
+
+		$this->assertFalse(
+			$processor->has_self_closing_flag(),
+			'Trailing slash in unquoted attribute value should not be interpreted as a self-closing flag.'
+		);
+	}
+
 	/**
 	 * @ticket 56299
 	 *