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* HTML API: WP_HTML_Open_Elements class
* Core class used by the HTML processor during HTML parsing
* for managing the stack of open elements.
* 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
* @see https://html.spec.whatwg.org/#stack-of-open-elements
class WP_HTML_Open_Elements {
* Holds the stack of open element references.
* 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.
private $has_p_in_button_scope = false;
* A function that will be called when an item is popped off the stack of open elements.
* The function will be called with the popped item as its argument.
private $pop_handler = null;
* A function that will be called when an item is pushed onto the stack of open elements.
* The function will be called with the pushed item as its argument.
private $push_handler = null;
* Sets a pop handler that will be called when an item is popped off the stack of
* The function will be called with the pushed item as its argument.
* @param Closure $handler The handler function.
public function set_pop_handler( Closure $handler ) {
$this->pop_handler = $handler;
* Sets a push handler that will be called when an item is pushed onto the stack of
* The function will be called with the pushed item as its argument.
* @param Closure $handler The handler function.
public function set_push_handler( Closure $handler ) {
$this->push_handler = $handler;
* Reports if a specific node is in the stack of open elements.
* @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 ) {
* Returns how many nodes are currently in the stack of open elements.
* @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.
* @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.
* This function skips checking for the termination list because there
* are no supported elements which appear in the termination list.
* @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 ) {
'(internal: H1 through H6 - do not use)' === $tag_name &&
in_array( $node->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )
switch ( $node->node_name ) {
if ( in_array( $node->node_name, $termination_list, true ) ) {
* Returns whether a particular element is in scope.
* @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(
* 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
* Returns whether a particular element is in list item scope.
* @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(
// There are more elements that belong here which aren't currently supported.
* Returns whether a particular element is in button scope.
* @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.
* @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.
* @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.
* @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.
* @see https://html.spec.whatwg.org/#stack-of-open-elements
* @return bool Whether a node was popped off of the stack.
$item = array_pop( $this->stack );
if ( 'context-node' === $item->bookmark_name ) {
$this->after_element_pop( $item );
* Pops nodes off of the stack of open elements until one with the given tag name has been popped.
* @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 ) {
if ( 'context-node' === $item->bookmark_name ) {
'(internal: H1 through H6 - do not use)' === $tag_name &&
in_array( $item->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )
if ( $tag_name === $item->node_name ) {
* Pushes a node onto the stack of open elements.
* @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.
* @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 ) {
if ( 'context-node' === $token->bookmark_name ) {
foreach ( $this->walk_up() as $position_from_end => $item ) {
if ( $token->bookmark_name !== $item->bookmark_name ) {
$position_from_start = $this->count() - $position_from_end - 1;
array_splice( $this->stack, $position_from_start, 1 );
$this->after_element_pop( $item );
* 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.
* $html = '<em><strong><a>We are here';
* foreach ( $stack->walk_down() as $node ) {
* echo "{$node->node_name} -> ";
* To start with the most-recently added element and walk towards the top,
* see WP_HTML_Open_Elements::walk_up().
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.
* $html = '<em><strong><a>We are here';
* foreach ( $stack->walk_up() as $node ) {
* echo "{$node->node_name} -> ";
* To start with the first added element and walk towards the bottom,
* see WP_HTML_Open_Elements::walk_down().
* @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;
* 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.
* @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 ) {
$this->has_p_in_button_scope = false;
$this->has_p_in_button_scope = true;
if ( null !== $this->push_handler ) {
( $this->push_handler )( $item );
It is recommended that you Edit text format, this type of Fix handles quite a lot in one request
