wp-includes/html-api/class-wp-html-processor.php:5107Creates a new bookmark for the currently-matched token and returns the generated name.
string|false private function bookmark_token() { if ( ! parent::set_bookmark( ++$this->bookmark_counter ) ) { $this->last_error = self::ERROR_EXCEEDED_MAX_BOOKMARKS; throw new Exception( 'could not allocate bookmark' ); } return "{$this->bookmark_counter}"; }Introduced in 6.4.0. One change between 6.7.7 and 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
string|false to string.verified against sourcesrc/wp-includes/html-api/class-wp-html-processor.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.