diff -r 48c4eec2b7e6 -r 8c2e4d02f4ef wp/wp-includes/html-api/class-wp-html-unsupported-exception.php
--- a/wp/wp-includes/html-api/class-wp-html-unsupported-exception.php	Fri Sep 05 18:40:08 2025 +0200
+++ b/wp/wp-includes/html-api/class-wp-html-unsupported-exception.php	Fri Sep 05 18:52:52 2025 +0200
@@ -21,11 +21,95 @@
  * operation and signify that the given HTML cannot be processed.
  *
  * @since 6.4.0
+ * @since 6.7.0 Gained contextual information for use in debugging parse failures.
  *
  * @access private
  *
  * @see WP_HTML_Processor
  */
 class WP_HTML_Unsupported_Exception extends Exception {
+	/**
+	 * Name of the matched token when the exception was raised,
+	 * if matched on a token.
+	 *
+	 * This does not imply that the token itself was unsupported, but it
+	 * may have been the case that the token triggered part of the HTML
+	 * parsing that isn't supported, such as the adoption agency algorithm.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @var string
+	 */
+	public $token_name;
 
+	/**
+	 * Number of bytes into the input HTML document where the parser was
+	 * parsing when the exception was raised.
+	 *
+	 * Use this to reconstruct context for the failure.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @var int
+	 */
+	public $token_at;
+
+	/**
+	 * Full raw text of the matched token when the exception was raised,
+	 * if matched on a token.
+	 *
+	 * Whereas the `$token_name` will be normalized, this contains the full
+	 * raw text of the token, including original casing, duplicated attributes,
+	 * and other syntactic variations that are normally abstracted in the HTML API.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @var string
+	 */
+	public $token;
+
+	/**
+	 * Stack of open elements when the exception was raised.
+	 *
+	 * Use this to trace the parsing circumstances which led to the exception.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @var string[]
+	 */
+	public $stack_of_open_elements = array();
+
+	/**
+	 * List of active formatting elements when the exception was raised.
+	 *
+	 * Use this to trace the parsing circumstances which led to the exception.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @var string[]
+	 */
+	public $active_formatting_elements = array();
+
+	/**
+	 * Constructor function.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @param string   $message                    Brief message explaining what is unsupported, the reason this exception was raised.
+	 * @param string   $token_name                 Normalized name of matched token when this exception was raised.
+	 * @param int      $token_at                   Number of bytes into source HTML document where matched token starts.
+	 * @param string   $token                      Full raw text of matched token when this exception was raised.
+	 * @param string[] $stack_of_open_elements     Stack of open elements when this exception was raised.
+	 * @param string[] $active_formatting_elements List of active formatting elements when this exception was raised.
+	 */
+	public function __construct( string $message, string $token_name, int $token_at, string $token, array $stack_of_open_elements, array $active_formatting_elements ) {
+		parent::__construct( $message );
+
+		$this->token_name = $token_name;
+		$this->token_at   = $token_at;
+		$this->token      = $token;
+
+		$this->stack_of_open_elements     = $stack_of_open_elements;
+		$this->active_formatting_elements = $active_formatting_elements;
+	}
 }