ting elements to the stack.
		 */
		// > Add element to the list of active formatting elements.
		$this->stack[] = $token;
	}

	/**
	 * Removes a node from the stack of active formatting elements.
	 *
	 * @since 6.4.0
	 *
	 * @param WP_HTML_Token $token Remove this node from the stack, if it's there already.
	 * @return bool Whether the node was found and removed from the stack of active formatting elements.
	 */
	public function remove_node( WP_HTML_Token $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 );
			return true;
		}

		return false;
	}

	/**
	 * Steps through the stack of active formatting 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_Active_Formatting_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 active formatting 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_Active_Formatting_Elements::walk_down().
	 *
	 * @since 6.4.0
	 */
	public function walk_up() {
		for ( $i = count( $this->stack ) - 1; $i >= 0; $i-- ) {
			yield $this->stack[ $i ];
		}
	}

	/**
	 * Clears the list of active formatting elements up to the last marker.
	 *
	 * > When the steps below require the UA to clear the list of active formatting elements up to
	 * > the last marker, the UA must perform the following steps:
	 * >
	 * > 1. Let entry be the last (most recently added) entry in the list of active
	 * >    formatting elements.
	 * > 2. Remove entry from the list of active formatting elements.
	 * > 3. If entry was a marker, then stop the algorithm at this point.
	 * >    The list has been cleared up to the last marker.
	 * > 4. Go to step 1.
	 *
	 * @see https://html.spec.whatwg.org/multipage/parsing.html#clear-the-list-of-active-formatting-elements-up-to-the-last-marker
	 *
	 * @since 6.7.0
	 */
	public function clear_up_to_last_marker(): void {
		foreach ( $this->walk_up() as $item ) {
			array_pop( $this->stack );
			if ( 'marker' === $item->node_name ) {
				break;
			}
		}
	}
}