WP_HTML_Tag_Processor::apply_attributes_updates( int $shift_this_point ): int

Source

 * @see WP_HTML_Tag_Processor::$lexical_updates
 * @see WP_HTML_Tag_Processor::$classname_updates
 */
private function class_name_updates_to_attributes_updates(): void {
	if ( count( $this->classname_updates ) === 0 ) {
		return;
	}

	$existing_class = $this->get_enqueued_attribute_value( 'class' );
	if ( null === $existing_class || true === $existing_class ) {
		$existing_class = '';
	}

	if ( false === $existing_class && isset( $this->attributes['class'] ) ) {
		$existing_class = substr(
			$this->html,
			$this->attributes['class']->value_starts_at,
			$this->attributes['class']->value_length
		);
	}

	if ( false === $existing_class ) {
		$existing_class = '';
	}

	/**
	 * Updated "class" attribute value.
	 *
	 * This is incrementally built while scanning through the existing class
	 * attribute, skipping removed classes on the way, and then appending
	 * added classes at the end. Only when finished processing will the
	 * value contain the final new value.

	 * @var string $class
	 */
	$class = '';

	/**
	 * Tracks the cursor position in the existing
	 * class attribute value while parsing.
	 *
	 * @var int $at
	 */
	$at = 0;

	/**
	 * Indicates if there's any need to modify the existing class attribute.
	 *
	 * If a call to `add_class()` and `remove_class()` wouldn't impact
	 * the `class` attribute value then there's no need to rebuild it.
	 * For example, when adding a class that's already present or
	 * removing one that isn't.
	 *
	 * This flag enables a performance optimization when none of the enqueued
	 * class updates would impact the `class` attribute; namely, that the
	 * processor can continue without modifying the input document, as if
	 * none of the `add_class()` or `remove_class()` calls had been made.
	 *
	 * This flag is set upon the first change that requires a string update.
	 *
	 * @var bool $modified
	 */
	$modified = false;

	$seen      = array();
	$to_remove = array();
	$is_quirks = self::QUIRKS_MODE === $this->compat_mode;
	if ( $is_quirks ) {
		foreach ( $this->classname_updates as $updated_name => $action ) {
			if ( self::REMOVE_CLASS === $action ) {
				$to_remove[] = strtolower( $updated_name );
			}
		}
	} else {
		foreach ( $this->classname_updates as $updated_name => $action ) {
			if ( self::REMOVE_CLASS === $action ) {
				$to_remove[] = $updated_name;
			}
		}
	}

	// Remove unwanted classes by only copying the new ones.
	$existing_class_length = strlen( $existing_class );
	while ( $at < $existing_class_length ) {
		// Skip to the first non-whitespace character.
		$ws_at     = $at;
		$ws_length = strspn( $existing_class, " \t\f\r\n", $ws_at );
		$at       += $ws_length;

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