class WP_HTML_Open_Elements {}

In this article

Core class used by the HTML processor during HTML parsing for managing the stack of open elements.

Description

This class is designed for internal use by the HTML processor.

Initially, the stack of open elements is empty. The stack grows downwards; the topmost node on the stack is the first one added to the stack, and the bottommost node of the stack is the most recently added node in the stack (notwithstanding when the stack is manipulated in a random access fashion as part of the handling for misnested tags).

See also

Methods

NameDescription
WP_HTML_Open_Elements::after_element_popUpdates internal flags after removing an element.
WP_HTML_Open_Elements::after_element_pushUpdates internal flags after adding an element.
WP_HTML_Open_Elements::contains_nodeReports if a specific node is in the stack of open elements.
WP_HTML_Open_Elements::countReturns how many nodes are currently in the stack of open elements.
WP_HTML_Open_Elements::current_nodeReturns the node at the end of the stack of open elements, if one exists. If the stack is empty, returns null.
WP_HTML_Open_Elements::has_element_in_button_scopeReturns whether a particular element is in button scope.
WP_HTML_Open_Elements::has_element_in_list_item_scopeReturns whether a particular element is in list item scope.
WP_HTML_Open_Elements::has_element_in_scopeReturns whether a particular element is in scope.
WP_HTML_Open_Elements::has_element_in_select_scopeReturns whether a particular element is in select scope.
WP_HTML_Open_Elements::has_element_in_specific_scopeReturns whether an element is in a specific scope.
WP_HTML_Open_Elements::has_element_in_table_scopeReturns whether a particular element is in table scope.
WP_HTML_Open_Elements::has_p_in_button_scopeReturns whether a P is in BUTTON scope.
WP_HTML_Open_Elements::popPops a node off of the stack of open elements.
WP_HTML_Open_Elements::pop_untilPops nodes off of the stack of open elements until one with the given tag name has been popped.
WP_HTML_Open_Elements::pushPushes a node onto the stack of open elements.
WP_HTML_Open_Elements::remove_nodeRemoves a specific node from the stack of open elements.
WP_HTML_Open_Elements::walk_downSteps through the stack of open elements, starting with the top element (added first) and walking downwards to the one added last.
WP_HTML_Open_Elements::walk_upSteps through the stack of open elements, starting with the bottom element (added last) and walking upwards to the one added first.

Source

class WP_HTML_Open_Elements {
	/**
	 * Holds the stack of open element references.
	 *
	 * @since 6.4.0
	 *
	 * @var WP_HTML_Token[]
	 */
	public $stack = array();

	/**
	 * Whether a P element is in button scope currently.
	 *
	 * This class optimizes scope lookup by pre-calculating
	 * this value when elements are added and removed to the
	 * stack of open elements which might change its value.
	 * This avoids frequent iteration over the stack.
	 *
	 * @since 6.4.0
	 *
	 * @var bool
	 */
	private $has_p_in_button_scope = false;

	/**
	 * Reports if a specific node is in the stack of open elements.
	 *
	 * @since 6.4.0
	 *
	 * @param WP_HTML_Token $token Look for this node in the stack.
	 * @return bool Whether the referenced node is in the stack of open elements.
	 */
	public function contains_node( $token ) {
		foreach ( $this->walk_up() as $item ) {
			if ( $token->bookmark_name === $item->bookmark_name ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * Returns how many nodes are currently in the stack of open elements.
	 *
	 * @since 6.4.0
	 *
	 * @return int How many node are in the stack of open elements.
	 */
	public function count() {
		return count( $this->stack );
	}

	/**
	 * Returns the node at the end of the stack of open elements,
	 * if one exists. If the stack is empty, returns null.
	 *
	 * @since 6.4.0
	 *
	 * @return WP_HTML_Token|null Last node in the stack of open elements, if one exists, otherwise null.
	 */
	public function current_node() {
		$current_node = end( $this->stack );

		return $current_node ? $current_node : null;
	}

	/**
	 * Returns whether an element is in a specific scope.
	 *
	 * ## HTML Support
	 *
	 * This function skips checking for the termination list because there
	 * are no supported elements which appear in the termination list.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-the-specific-scope
	 *
	 * @param string   $tag_name         Name of tag check.
	 * @param string[] $termination_list List of elements that terminate the search.
	 * @return bool Whether the element was found in a specific scope.
	 */
	public function has_element_in_specific_scope( $tag_name, $termination_list ) {
		foreach ( $this->walk_up() as $node ) {
			if ( $node->node_name === $tag_name ) {
				return true;
			}

			if (
				'(internal: H1 through H6 - do not use)' === $tag_name &&
				in_array( $node->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )
			) {
				return true;
			}

			switch ( $node->node_name ) {
				case 'HTML':
					return false;
			}

			if ( in_array( $node->node_name, $termination_list, true ) ) {
				return false;
			}
		}

		return false;
	}

	/**
	 * Returns whether a particular element is in scope.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-scope
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether given element is in scope.
	 */
	public function has_element_in_scope( $tag_name ) {
		return $this->has_element_in_specific_scope(
			$tag_name,
			array(

				/*
				 * Because it's not currently possible to encounter
				 * one of the termination elements, they don't need
				 * to be listed here. If they were, they would be
				 * unreachable and only waste CPU cycles while
				 * scanning through HTML.
				 */
			)
		);
	}

	/**
	 * Returns whether a particular element is in list item scope.
	 *
	 * @since 6.4.0
	 * @since 6.5.0 Implemented: no longer throws on every invocation.
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-list-item-scope
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether given element is in scope.
	 */
	public function has_element_in_list_item_scope( $tag_name ) {
		return $this->has_element_in_specific_scope(
			$tag_name,
			array(
				// There are more elements that belong here which aren't currently supported.
				'OL',
				'UL',
			)
		);
	}

	/**
	 * Returns whether a particular element is in button scope.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-button-scope
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether given element is in scope.
	 */
	public function has_element_in_button_scope( $tag_name ) {
		return $this->has_element_in_specific_scope( $tag_name, array( 'BUTTON' ) );
	}

	/**
	 * Returns whether a particular element is in table scope.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-table-scope
	 *
	 * @throws WP_HTML_Unsupported_Exception Always until this function is implemented.
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether given element is in scope.
	 */
	public function has_element_in_table_scope( $tag_name ) {
		throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on table scope.' );

		return false; // The linter requires this unreachable code until the function is implemented and can return.
	}

	/**
	 * Returns whether a particular element is in select scope.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-select-scope
	 *
	 * @throws WP_HTML_Unsupported_Exception Always until this function is implemented.
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether given element is in scope.
	 */
	public function has_element_in_select_scope( $tag_name ) {
		throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on select scope.' );

		return false; // The linter requires this unreachable code until the function is implemented and can return.
	}

	/**
	 * Returns whether a P is in BUTTON scope.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#has-an-element-in-button-scope
	 *
	 * @return bool Whether a P is in BUTTON scope.
	 */
	public function has_p_in_button_scope() {
		return $this->has_p_in_button_scope;
	}

	/**
	 * Pops a node off of the stack of open elements.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#stack-of-open-elements
	 *
	 * @return bool Whether a node was popped off of the stack.
	 */
	public function pop() {
		$item = array_pop( $this->stack );

		if ( null === $item ) {
			return false;
		}

		$this->after_element_pop( $item );
		return true;
	}

	/**
	 * Pops nodes off of the stack of open elements until one with the given tag name has been popped.
	 *
	 * @since 6.4.0
	 *
	 * @see WP_HTML_Open_Elements::pop
	 *
	 * @param string $tag_name Name of tag that needs to be popped off of the stack of open elements.
	 * @return bool Whether a tag of the given name was found and popped off of the stack of open elements.
	 */
	public function pop_until( $tag_name ) {
		foreach ( $this->walk_up() as $item ) {
			$this->pop();

			if (
				'(internal: H1 through H6 - do not use)' === $tag_name &&
				in_array( $item->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )
			) {
				return true;
			}

			if ( $tag_name === $item->node_name ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * Pushes a node onto the stack of open elements.
	 *
	 * @since 6.4.0
	 *
	 * @see https://html.spec.whatwg.org/#stack-of-open-elements
	 *
	 * @param WP_HTML_Token $stack_item Item to add onto stack.
	 */
	public function push( $stack_item ) {
		$this->stack[] = $stack_item;
		$this->after_element_push( $stack_item );
	}

	/**
	 * Removes a specific node from the stack of open elements.
	 *
	 * @since 6.4.0
	 *
	 * @param WP_HTML_Token $token The node to remove from the stack of open elements.
	 * @return bool Whether the node was found and removed from the stack of open elements.
	 */
	public function remove_node( $token ) {
		foreach ( $this->walk_up() as $position_from_end => $item ) {
			if ( $token->bookmark_name !== $item->bookmark_name ) {
				continue;
			}

			$position_from_start = $this->count() - $position_from_end - 1;
			array_splice( $this->stack, $position_from_start, 1 );
			$this->after_element_pop( $item );
			return true;
		}

		return false;
	}


	/**
	 * Steps through the stack of open elements, starting with the top element
	 * (added first) and walking downwards to the one added last.
	 *
	 * This generator function is designed to be used inside a "foreach" loop.
	 *
	 * Example:
	 *
	 *     $html = '<em><strong><a>We are here';
	 *     foreach ( $stack->walk_down() as $node ) {
	 *         echo "{$node->node_name} -> ";
	 *     }
	 *     > EM -> STRONG -> A ->
	 *
	 * To start with the most-recently added element and walk towards the top,
	 * see WP_HTML_Open_Elements::walk_up().
	 *
	 * @since 6.4.0
	 */
	public function walk_down() {
		$count = count( $this->stack );

		for ( $i = 0; $i < $count; $i++ ) {
			yield $this->stack[ $i ];
		}
	}

	/**
	 * Steps through the stack of open elements, starting with the bottom element
	 * (added last) and walking upwards to the one added first.
	 *
	 * This generator function is designed to be used inside a "foreach" loop.
	 *
	 * Example:
	 *
	 *     $html = '<em><strong><a>We are here';
	 *     foreach ( $stack->walk_up() as $node ) {
	 *         echo "{$node->node_name} -> ";
	 *     }
	 *     > A -> STRONG -> EM ->
	 *
	 * To start with the first added element and walk towards the bottom,
	 * see WP_HTML_Open_Elements::walk_down().
	 *
	 * @since 6.4.0
	 * @since 6.5.0 Accepts $above_this_node to start traversal above a given node, if it exists.
	 *
	 * @param ?WP_HTML_Token $above_this_node Start traversing above this node, if provided and if the node exists.
	 */
	public function walk_up( $above_this_node = null ) {
		$has_found_node = null === $above_this_node;

		for ( $i = count( $this->stack ) - 1; $i >= 0; $i-- ) {
			$node = $this->stack[ $i ];

			if ( ! $has_found_node ) {
				$has_found_node = $node === $above_this_node;
				continue;
			}

			yield $node;
		}
	}

	/*
	 * Internal helpers.
	 */

	/**
	 * Updates internal flags after adding an element.
	 *
	 * Certain conditions (such as "has_p_in_button_scope") are maintained here as
	 * flags that are only modified when adding and removing elements. This allows
	 * the HTML Processor to quickly check for these conditions instead of iterating
	 * over the open stack elements upon each new tag it encounters. These flags,
	 * however, need to be maintained as items are added and removed from the stack.
	 *
	 * @since 6.4.0
	 *
	 * @param WP_HTML_Token $item Element that was added to the stack of open elements.
	 */
	public function after_element_push( $item ) {
		/*
		 * When adding support for new elements, expand this switch to trap
		 * cases where the precalculated value needs to change.
		 */
		switch ( $item->node_name ) {
			case 'BUTTON':
				$this->has_p_in_button_scope = false;
				break;

			case 'P':
				$this->has_p_in_button_scope = true;
				break;
		}
	}

	/**
	 * Updates internal flags after removing an element.
	 *
	 * Certain conditions (such as "has_p_in_button_scope") are maintained here as
	 * flags that are only modified when adding and removing elements. This allows
	 * the HTML Processor to quickly check for these conditions instead of iterating
	 * over the open stack elements upon each new tag it encounters. These flags,
	 * however, need to be maintained as items are added and removed from the stack.
	 *
	 * @since 6.4.0
	 *
	 * @param WP_HTML_Token $item Element that was removed from the stack of open elements.
	 */
	public function after_element_pop( $item ) {
		/*
		 * When adding support for new elements, expand this switch to trap
		 * cases where the precalculated value needs to change.
		 */
		switch ( $item->node_name ) {
			case 'BUTTON':
				$this->has_p_in_button_scope = $this->has_element_in_button_scope( 'P' );
				break;

			case 'P':
				$this->has_p_in_button_scope = $this->has_element_in_button_scope( 'P' );
				break;
		}
	}
}

Changelog

VersionDescription
6.4.0Introduced.

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