//html.spec.whatwg.org/#has-an-element-in-select-scope
	 *
	 * @param string $tag_name Name of tag to check.
	 * @return bool Whether the given element is in SELECT scope.
	 */
	public function has_element_in_select_scope( string $tag_name ): bool {
		foreach ( $this->walk_up() as $node ) {
			if ( $node->node_name === $tag_name ) {
				return true;
			}

			if (
				'OPTION' !== $node->node_name &&
				'OPTGROUP' !== $node->node_name
			) {
				return false;
			}
		}

		return false;
	}

	/**
	 * 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(): bool {
		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(): bool {
		$item = array_pop( $this->stack );
		if ( null === $item ) {
			return false;
		}

		if ( 'context-node' === $item->bookmark_name ) {
			$this->stack[] = $item;
			return false;
		}

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

	/**
	 * Pops nodes off of the stack of open elements until an HTML tag with the given name has been popped.
	 *
	 * @since 6.4.0
	 *
	 * @see WP_HTML_Open_Elements::pop
	 *
	 * @param string $html_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( string $html_tag_name ): bool {
		foreach ( $this->walk_up() as $item ) {
			$this->pop();

			if ( 'html' !== $item->namespace ) {
				continue;
			}

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

			if ( $html_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( WP_HTML_Token $stack_item ): void {
		$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( WP_HTML_Token $token ): bool {
		if ( 'context-node' === $token->bookmark_name ) {
			return false;
		}

		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|null $above_this_node Optional. Start traversing above this node,
	 *                                            if provided and if the node exists.
	 */
	public function walk_up( ?WP_HTML_Token $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( WP_HTML_Token $item ): void {
		$namespaced_name = 'html' === $item->namespace
			? $item->node_name
			: "{$item->namespace} {$item->node_name}";

		/*
		 * When adding support for new elements, expand this switch to trap
		 * cases where the precalculated value needs to change.
		 */
		switch ( $namespaced_name ) {
			case 'APPLET':
			case 'BUTTON':
			case 'CAPTION':
			case 'HTML':
			case 'TABLE':
			case 'TD':
			case 'TH':
			case 'MARQUEE':
			case 'OBJECT':
			case 'TEMPLATE':
			case 'math MI':
			case 'math MO':
			case 'math MN':
			case 'math MS':
			case 'math MTEXT':
			case 'math ANNOTATION-XML':
			case 'svg FOREIGNOBJECT':
			case 'svg DESC':
			case 'svg TITLE':
				$this->has_p_in_button_scope = false;
				break;

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

		if ( null !== $this->push_handler ) {
			( $this->push_handler )( $item );
		}
	}

	/**
	 * 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( WP_HTML_Token $item ): void {
		/*
		 * When adding support for new elements, expand this switch to trap
		 * cases where the precalculated value needs to change.
		 */
		switch ( $item->node_name ) {
			case 'APPLET':
			case 'BUTTON':
			case 'CAPTION':
			case 'HTML':
			case 'P':
			case 'TABLE':
			case 'TD':
			case 'TH':
			case 'MARQUEE':
			case 'OBJECT':
			case 'TEMPLATE':
			case 'math MI':
			case 'math MO':
			case 'math MN':
			case 'math MS':
			case 'math MTEXT':
			case 'math ANNOTATION-XML':
			case 'svg FOREIGNOBJECT':
			case 'svg DESC':
			case 'svg TITLE':
				$this->has_p_in_button_scope = $this->has_element_in_button_scope( 'P' );
				break;
		}

		if ( null !== $this->pop_handler ) {
			( $this->pop_handler )( $item );
		}
	}

	/**
	 * Clear the stack back to a table context.
	 *
	 * > When the steps above require the UA to clear the stack back to a table context, it means
	 * > that the UA must, while the current node is not a table, template, or html element, pop
	 * > elements from the stack of open elements.
	 *
	 * @see https://html.spec.whatwg.org/multipage/parsing.html#clear-the-stack-back-to-a-table-context
	 *
	 * @since 6.7.0
	 */
	public function clear_to_table_context(): void {
		foreach ( $this->walk_up() as $item ) {
			if (
				'TABLE' === $item->node_name ||
				'TEMPLATE' === $item->node_name ||
				'HTML' === $item->node_name
			) {
				break;
			}
			$this->pop();
		}
	}

	/**
	 * Clear the stack back to a table body context.
	 *
	 * > When the steps above require the UA to clear the stack back to a table body context, it
	 * > means that the UA must, while the current node is not a tbody, tfoot, thead, template, or
	 * > html element, pop elements from the stack of open elements.
	 *
	 * @see https://html.spec.whatwg.org/multipage/parsing.html#clear-the-stack-back-to-a-table-body-context
	 *
	 * @since 6.7.0
	 */
	public function clear_to_table_body_context(): void {
		foreach ( $this->walk_up() as $item ) {
			if (
				'TBODY' === $item->node_name ||
				'TFOOT' === $item->node_name ||
				'THEAD' === $item->node_name ||
				'TEMPLATE' === $item->node_name ||
				'HTML' === $item->node_name
			) {
				break;
			}
			$this->pop();
		}
	}

	/**
	 * Clear the stack back to a table row context.
	 *
	 * > When the steps above require the UA to clear the stack back to a table row context, it
	 * > means that the UA must, while the current node is not a tr, template, or html element, pop
	 * > elements from the stack of open elements.
	 *
	 * @see https://html.spec.whatwg.org/multipage/parsing.html#clear-the-stack-back-to-a-table-row-context
	 *
	 * @since 6.7.0
	 */
	public function clear_to_table_row_context(): void {
		foreach ( $this->walk_up() as $item ) {
			if (
				'TR' === $item->node_name ||
				'TEMPLATE' === $item->node_name ||
				'HTML' === $item->node_name
			) {
				break;
			}
			$this->pop();
		}
	}

	/**
	 * Wakeup magic method.
	 *
	 * @since 6.6.0
	 */
	public function __wakeup() {
		throw new \LogicException( __CLASS__ . ' should never be unserialized' );
	}
}
er])) {
				/*
				 * Integrators who cannot yet upgrade to the PSR-4 class names can silence deprecations
				 * by defining a `REQUESTS_SILENCE_PSR0_DEPRECATIONS` constant and setting it to `true`.
				 * The constant needs to be defined before the first deprecated class is requested
				 * via this autoloader.
				 */
				if (!defined('REQUESTS_SILENCE_PSR0_DEPRECATIONS') || REQUESTS_SILENCE_PSR0_DEPRECATIONS !== true) {
					// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_trigger_error
					trigger_error(
						'The PSR-0 `Requests_...` class names in the Requests library are deprecated.'
						. ' Switch to the PSR-4 `WpOrg\Requests\...` class names at your earliest convenience.',
						E_USER_DEPRECATED
					);

					// Prevent the deprecation notice from being thrown twice.
					if (!defined('REQUESTS_SILENCE_PSR0_DEPRECATIONS')) {
						define('REQUESTS_SILENCE_PSR0_DEPRECATIONS', true);
					}
				}

				// Create an alias and let the autoloader recursively kick in to load the PSR-4 class.
				return class_alias(self::$deprecated_classes[$class_lower], $class_name, true);
			}

			return false;
		}
	}
}