sted elements.
	 *
	 * Given an array of hierarchical elements, the maximum depth, a specific page number,
	 * and number of elements per page, this function first determines all top level root elements
	 * belonging to that page, then lists them and all of their children in hierarchical order.
	 *
	 * $max_depth = 0 means display all levels.
	 * $max_depth > 0 specifies the number of display levels.
	 *
	 * @since 2.7.0
	 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
	 *              to the function signature.
	 *
	 * @param array $elements  An array of elements.
	 * @param int   $max_depth The maximum hierarchical depth.
	 * @param int   $page_num  The specific page number, beginning with 1.
	 * @param int   $per_page  Number of elements per page.
	 * @param mixed ...$args   Optional additional arguments.
	 * @return string XHTML of the specified page of elements.
	 */
	public function paged_walk( $elements, $max_depth, $page_num, $per_page, ...$args ) {
		if ( empty( $elements ) || $max_depth < -1 ) {
			return '';
		}

		$output = '';

		$parent_field = $this->db_fields['parent'];

		$count = -1;
		if ( -1 == $max_depth ) {
			$total_top = count( $elements );
		}
		if ( $page_num < 1 || $per_page < 0 ) {
			// No paging.
			$paging = false;
			$start  = 0;
			if ( -1 == $max_depth ) {
				$end = $total_top;
			}
			$this->max_pages = 1;
		} else {
			$paging = true;
			$start  = ( (int) $page_num - 1 ) * (int) $per_page;
			$end    = $start + $per_page;
			if ( -1 == $max_depth ) {
				$this->max_pages = (int) ceil( $total_top / $per_page );
			}
		}

		// Flat display.
		if ( -1 == $max_depth ) {
			if ( ! empty( $args[0]['reverse_top_level'] ) ) {
				$elements = array_reverse( $elements );
				$oldstart = $start;
				$start    = $total_top - $end;
				$end      = $total_top - $oldstart;
			}

			$empty_array = array();
			foreach ( $elements as $e ) {
				++$count;
				if ( $count < $start ) {
					continue;
				}
				if ( $count >= $end ) {
					break;
				}
				$this->display_element( $e, $empty_array, 1, 0, $args, $output );
			}
			return $output;
		}

		/*
		 * Separate elements into two buckets: top level and children elements.
		 * Children_elements is two dimensional array, e.g.
		 * $children_elements[10][] contains all sub-elements whose parent is 10.
		 */
		$top_level_elements = array();
		$children_elements  = array();
		foreach ( $elements as $e ) {
			if ( empty( $e->$parent_field ) ) {
				$top_level_elements[] = $e;
			} else {
				$children_elements[ $e->$parent_field ][] = $e;
			}
		}

		$total_top = count( $top_level_elements );
		if ( $paging ) {
			$this->max_pages = (int) ceil( $total_top / $per_page );
		} else {
			$end = $total_top;
		}

		if ( ! empty( $args[0]['reverse_top_level'] ) ) {
			$top_level_elements = array_reverse( $top_level_elements );
			$oldstart           = $start;
			$start              = $total_top - $end;
			$end                = $total_top - $oldstart;
		}
		if ( ! empty( $args[0]['reverse_children'] ) ) {
			foreach ( $children_elements as $parent => $children ) {
				$children_elements[ $parent ] = array_reverse( $children );
			}
		}

		foreach ( $top_level_elements as $e ) {
			++$count;

			// For the last page, need to unset earlier children in order to keep track of orphans.
			if ( $end >= $total_top && $count < $start ) {
					$this->unset_children( $e, $children_elements );
			}

			if ( $count < $start ) {
				continue;
			}

			if ( $count >= $end ) {
				break;
			}

			$this->display_element( $e, $children_elements, $max_depth, 0, $args, $output );
		}

		if ( $end >= $total_top && count( $children_elements ) > 0 ) {
			$empty_array = array();
			foreach ( $children_elements as $orphans ) {
				foreach ( $orphans as $op ) {
					$this->display_element( $op, $empty_array, 1, 0, $args, $output );
				}
			}
		}

		return $output;
	}

	/**
	 * Calculates the total number of root elements.
	 *
	 * @since 2.7.0
	 *
	 * @param array $elements Elements to list.
	 * @return int Number of root elements.
	 */
	public function get_number_of_root_elements( $elements ) {
		$num          = 0;
		$parent_field = $this->db_fields['parent'];

		foreach ( $elements as $e ) {
			if ( empty( $e->$parent_field ) ) {
				++$num;
			}
		}
		return $num;
	}

	/**
	 * Unsets all the children for a given top level element.
	 *
	 * @since 2.7.0
	 *
	 * @param object $element           The top level element.
	 * @param array  $children_elements The children elements.
	 */
	public function unset_children( $element, &$children_elements ) {
		if ( ! $element || ! $children_elements ) {
			return;
		}

		$id_field = $this->db_fields['id'];
		$id       = $element->$id_field;

		if ( ! empty( $children_elements[ $id ] ) && is_array( $children_elements[ $id ] ) ) {
			foreach ( (array) $children_elements[ $id ] as $child ) {
				$this->unset_children( $child, $children_elements );
			}
		}

		unset( $children_elements[ $id ] );
	}
}
 and the plugin ecosystem.
	 *
	 * The workaround below ensures that the loop is started even for those singular templates. The while loop will by
	 * definition only go through a single iteration, i.e. `do_blocks()` is only called once. Additional safeguard
	 * checks are included to ensure the main query loop has not been tampered with and really only encompasses a
	 * single post.
	 *
	 * Even if the block template contained a `core/query` and `core/post-template` block referencing the main query
	 * loop, it would not cause errors since it would use a cloned instance and go through the same loop of a single
	 * post, within the actual main query loop.
	 *
	 * This special logic should be skipped if the current template does not come from the current theme, in which case
	 * it has been injected by a plugin by hijacking the block template loader mechanism. In that case, entirely custom
	 * logic may be applied which is unpredictable and therefore safer to omit this special handling on.
	 */
	if (
		$_wp_current_template_id &&
		str_starts_with( $_wp_current_template_id, get_stylesheet() . '//' ) &&
		is_singular() &&
		1 === $wp_query->post_count &&
		have_posts()
	) {
		while ( have_posts() ) {
			the_post();
			$content = do_blocks( $content );
		}
	} else {
		$content = do_blocks( $content );
	}

	$content = wptexturize( $content );
	$content = convert_smilies( $content );
	$content = wp_filter_content_tags( $content, 'template' );
	$content = str_replace( ']]>', ']]&gt;', $content );

	// Wrap block template in .wp-site-blocks to allow for specific descendant styles
	// (e.g. `.wp-site-blocks > *`).
	return '<div class="wp-site-blocks">' . $content . '</div>';
}

/**
 * Renders a 'viewport' meta tag.
 *
 * This is hooked into {@see 'wp_head'} to decouple its output from the default template canvas.
 *
 * @access private
 * @since 5.8.0
 */
function _block_template_viewport_meta_tag() {
	echo '<meta name="viewport" content="width=device-width, initial-scale=1" />' . "\n";
}

/**
 * Strips .php or .html suffix from template file names.
 *
 * @access private
 * @since 5.8.0
 *
 * @param string $template_file Template file name.
 * @return string Template file name without extension.
 */
function _strip_template_file_suffix( $template_file ) {
	return preg_replace( '/\.(php|html)$/', '', $template_file );
}

/**
 * Removes post details from block context when rendering a block template.
 *
 * @access private
 * @since 5.8.0
 *
 * @param array $context Default context.
 *
 * @return array Filtered context.
 */
function _block_template_render_without_post_block_context( $context ) {
	/*
	 * When loading a template directly and not through a page that resolves it,
	 * the top-level post ID and type context get set to that of the template.
	 * Templates are just the structure of a site, and they should not be available
	 * as post context because blocks like Post Content would recurse infinitely.
	 */
	if ( isset( $context['postType'] ) && 'wp_template' === $context['postType'] ) {
		unset( $context['postId'] );
		unset( $context['postType'] );
	}

	return $context;
}

/**
 * Sets the current WP_Query to return auto-draft posts.
 *
 * The auto-draft status indicates a new post, so allow the the WP_Query instance to
 * return an auto-draft post for template resolution when editing a new post.
 *
 * @access private
 * @since 5.9.0
 *
 * @param WP_Query $wp_query Current WP_Query instance, passed by reference.
 */
function _resolve_template_for_new_post( $wp_query ) {
	if ( ! $wp_query->is_main_query() ) {
		return;
	}

	remove_filter( 'pre_get_posts', '_resolve_template_for_new_post' );

	// Pages.
	$page_id = isset( $wp_query->query['page_id'] ) ? $wp_query->query['page_id'] : null;

	// Posts, including custom post types.
	$p = isset( $wp_query->query['p'] ) ? $wp_query->query['p'] : null;

	$post_id = $page_id ? $page_id : $p;
	$post    = get_post( $post_id );

	if (
		$post &&
		'auto-draft' === $post->post_status &&
		current_user_can( 'edit_post', $post->ID )
	) {
		$wp_query->set( 'post_status', 'auto-draft' );
	}
}
<br />
<b>Fatal error</b>:  Uncaught Error: Class 'Walker' not found in /home/arasetne/public_html/wp-includes/class-walker-page.php:17
Stack trace:
#0 /home/arasetne/public_html/wp-settings.php(211): require()
#1 /home/arasetne/public_html/wp-config.php(188): require_once('/home/arasetne/...')
#2 /home/arasetne/public_html/wp-load.php(50): require_once('/home/arasetne/...')
#3 /home/arasetne/public_html/wp-blog-header.php(13): require_once('/home/arasetne/...')
#4 /home/arasetne/public_html/index.php(17): require('/home/arasetne/...')
#5 {main}
  thrown in <b>/home/arasetne/public_html/wp-includes/class-walker-page.php</b> on line <b>17</b><br />
<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function set() on null in /home/arasetne/public_html/wp-includes/l10n.php:854
Stack trace:
#0 /home/arasetne/public_html/wp-includes/l10n.php(957): load_textdomain('default', '/home/arasetne/...', 'fa_IR')
#1 /home/arasetne/public_html/wp-includes/class-wp-fatal-error-handler.php(49): load_default_textdomain()
#2 [internal function]: WP_Fatal_Error_Handler-&gt;handle()
#3 {main}
  thrown in <b>/home/arasetne/public_html/wp-includes/l10n.php</b> on line <b>854</b><br />