WP_HTML_Open_Elements

31class WP_HTML_Open_Elements {32	/**33	 * Holds the stack of open element references.34	 *35	 * @since 6.4.036	 *37	 * @var WP_HTML_Token[]38	 */39	public $stack = array();40 41	/**42	 * Whether a P element is in button scope currently.43	 *44	 * This class optimizes scope lookup by pre-calculating45	 * this value when elements are added and removed to the46	 * stack of open elements which might change its value.47	 * This avoids frequent iteration over the stack.48	 *49	 * @since 6.4.050	 *51	 * @var bool52	 */53	private $has_p_in_button_scope = false;54 55	/**56	 * A function that will be called when an item is popped off the stack of open elements.57	 *58	 * The function will be called with the popped item as its argument.59	 *60	 * @since 6.6.061	 *62	 * @var Closure|null63	 */64	private $pop_handler = null;65 66	/**67	 * A function that will be called when an item is pushed onto the stack of open elements.68	 *69	 * The function will be called with the pushed item as its argument.70	 *71	 * @since 6.6.072	 *73	 * @var Closure|null74	 */75	private $push_handler = null;76 77	/**78	 * Sets a pop handler that will be called when an item is popped off the stack of79	 * open elements.80	 *81	 * The function will be called with the pushed item as its argument.82	 *83	 * @since 6.6.084	 *85	 * @param Closure $handler The handler function.86	 */87	public function set_pop_handler( Closure $handler ): void {88		$this->pop_handler = $handler;89	}90 91	/**92	 * Sets a push handler that will be called when an item is pushed onto the stack of93	 * open elements.94	 *95	 * The function will be called with the pushed item as its argument.96	 *97	 * @since 6.6.098	 *99	 * @param Closure $handler The handler function.100	 */101	public function set_push_handler( Closure $handler ): void {102		$this->push_handler = $handler;103	}104 105	/**106	 * Returns the name of the node at the nth position on the stack107	 * of open elements, or `null` if no such position exists.108	 *109	 * Note that this uses a 1-based index, which represents the110	 * "nth item" on the stack, counting from the top, where the