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). * * @since 6.4.0 * * @access private * * @see https://html.spec.whatwg.org/#stack-of-open-elements * @see WP_HTML_Processor */ 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; } } 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 * * @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 ) { throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on list item scope.' ); } /** * 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( /* * 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 table scope. * * @since 6.4.0 * * @see https://html.spec.whatwg.org/#has-an-element-in-table-scope * * @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.' ); } /** * 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 * * @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.' ); } /** * 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 */ 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 ( $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 = '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 = '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 */ public function walk_up() { for ( $i = count( $this->stack ) - 1; $i >= 0; $i-- ) { yield $this->stack[ $i ]; } } /* * 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 '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 'P': $this->has_p_in_button_scope = $this->has_element_in_button_scope( 'P' ); break; } } }