eme|false Parent theme, or false if the active theme is not a child theme.
	 */
	public function parent() {
		return isset( $this->parent ) ? $this->parent : false;
	}

	/**
	 * Perform reinitialization tasks.
	 *
	 * Prevents a callback from being injected during unserialization of an object.
	 *
	 * @return void
	 */
	public function __wakeup() {
		if ( $this->parent && ! $this->parent instanceof self ) {
			throw new UnexpectedValueException();
		}
		if ( $this->headers && ! is_array( $this->headers ) ) {
			throw new UnexpectedValueException();
		}
		foreach ( $this->headers as $value ) {
			if ( ! is_string( $value ) ) {
				throw new UnexpectedValueException();
			}
		}
		$this->headers_sanitized = array();
	}

	/**
	 * Adds theme data to cache.
	 *
	 * Cache entries keyed by the theme and the type of data.
	 *
	 * @since 3.4.0
	 *
	 * @param string       $key  Type of data to store (theme, screenshot, headers, post_templates)
	 * @param array|string $data Data to store
	 * @return bool Return value from wp_cache_add()
	 */
	private function cache_add( $key, $data ) {
		return wp_cache_add( $key . '-' . $this->cache_hash, $data, 'themes', self::$cache_expiration );
	}

	/**
	 * Gets theme data from cache.
	 *
	 * Cache entries are keyed by the theme and the type of data.
	 *
	 * @since 3.4.0
	 *
	 * @param string $key Type of data to retrieve (theme, screenshot, headers, post_templates)
	 * @return mixed Retrieved data
	 */
	private function cache_get( $key ) {
		return wp_cache_get( $key . '-' . $this->cache_hash, 'themes' );
	}

	/**
	 * Clears the cache for the theme.
	 *
	 * @since 3.4.0
	 */
	public function cache_delete() {
		foreach ( array( 'theme', 'screenshot', 'headers', 'post_templates' ) as $key ) {
			wp_cache_delete( $key . '-' . $this->cache_hash, 'themes' );
		}
		$this->template          = null;
		$this->textdomain_loaded = null;
		$this->theme_root_uri    = null;
		$this->parent            = null;
		$this->errors            = null;
		$this->headers_sanitized = null;
		$this->name_translated   = null;
		$this->headers           = array();
		$this->__construct( $this->stylesheet, $this->theme_root );
	}

	/**
	 * Gets a raw, unformatted theme header.
	 *
	 * The header is sanitized, but is not translated, and is not marked up for display.
	 * To get a theme header for display, use the display() method.
	 *
	 * Use the get_template() method, not the 'Template' header, for finding the template.
	 * The 'Template' header is only good for what was written in the style.css, while
	 * get_template() takes into account where WordPress actually located the theme and
	 * whether it is actually valid.
	 *
	 * @since 3.4.0
	 *
	 * @param string $header Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
	 * @return string|array|false String or array (for Tags header) on success, false on failure.
	 */
	public function get( $header ) {
		if ( ! isset( $this->headers[ $header ] ) ) {
			return false;
		}

		if ( ! isset( $this->headers_sanitized ) ) {
			$this->headers_sanitized = $this->cache_get( 'headers' );
			if ( ! is_array( $this->headers_sanitized ) ) {
				$this->headers_sanitized = array();
			}
		}

		if ( isset( $this->headers_sanitized[ $header ] ) ) {
			return $this->headers_sanitized[ $header ];
		}

		// If themes are a persistent group, sanitize everything and cache it. One cache add is better than many cache sets.
		if ( self::$persistently_cache ) {
			foreach ( array_keys( $this->headers ) as $_header ) {
				$this->headers_sanitized[ $_header ] = $this->sanitize_header( $_header, $this->headers[ $_header ] );
			}
			$this->cache_add( 'headers', $this->headers_sanitized );
		} else {
			$this->headers_sanitized[ $header ] = $this->sanitize_header( $header, $this->headers[ $header ] );
		}

		return $this->headers_sanitized[ $header ];
	}

	/**
	 * Gets a theme header, formatted and translated for display.
	 *
	 * @since 3.4.0
	 *
	 * @param string $header    Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
	 * @param bool   $markup    Optional. Whether to mark up the header. Defaults to true.
	 * @param bool   $translate Optional. Whether to translate the header. Defaults to true.
	 * @return string|array|false Processed header. An array for Tags if `$markup` is false, string otherwise.
	 *                            False on failure.
	 */
	public function display( $header, $markup = true, $translate = true ) {
		$value = $this->get( $header );
		if ( false === $value ) {
			return false;
		}

		if ( $translate && ( empty( $value ) || ! $this->load_textdomain() ) ) {
			$translate = false;
		}

		if ( $translate ) {
			$value = $this->translate_header( $header, $value );
		}

		if ( $markup ) {
			$value = $this->markup_header( $header, $value, $translate );
		}

		return $value;
	}

	/**
	 * Sanitizes a theme header.
	 *
	 * @since 3.4.0
	 * @since 5.4.0 Added support for `Requires at least` and `Requires PHP` headers.
	 *
	 * @param string $header Theme header. Accepts 'Name', 'Description', 'Author', 'Version',
	 *                       'ThemeURI', 'AuthorURI', 'Status', 'Tags', 'RequiresWP', 'RequiresPHP'.
	 * @param string $value  Value to sanitize.
	 * @return string|array An array for Tags header, string otherwise.
	 */
	private function sanitize_header( $header, $value ) {
		switch ( $header ) {
			case 'Status':
				if ( ! $value ) {
					$value = 'publish';
					break;
				}
				// Fall through otherwise.
			case 'Name':
				static $header_tags = array(
					'abbr'    => array( 'title' => true ),
					'acronym' => array( 'title' => true ),
					'code'    => true,
					'em'      => true,
					'strong'  => true,
				);

				$value = wp_kses( $value, $header_tags );
				break;
			case 'Author':
				// There shouldn't be anchor tags in Author, but some themes like to be challenging.
			case 'Description':
				static $header_tags_with_a = array(
					'a'       => array(
						'href'  => true,
						'title' => true,
					),
					'abbr'    => array( 'title' => true ),
					'acronym' => array( 'title' => true ),
					'code'    => true,
					'em'      => true,
					'strong'  => true,
				);

				$value = wp_kses( $value, $header_tags_with_a );
				break;
			case 'ThemeURI':
			case 'AuthorURI':
				$value = esc_url_raw( $value );
				break;
			case 'Tags':
				$value = array_filter( array_map( 'trim', explode( ',', strip_tags( $value ) ) ) );
				break;
			case 'Version':
			case 'RequiresWP':
			case 'RequiresPHP':
				$value = strip_tags( $value );
				break;
		}

		return $value;
	}

	/**
	 * Marks up a theme header.
	 *
	 * @since 3.4.0
	 *
	 * @param string       $header    Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
	 * @param string|array $value     Value to mark up. An array for Tags header, string otherwise.
	 * @param string       $translate Whether the header has been translated.
	 * @return string Value, marked up.
	 */
	private function markup_header( $header, $value, $translate ) {
		switch ( $header ) {
			case 'Name':
				if ( empty( $value ) ) {
					$value = esc_html( $this->get_stylesheet() );
				}
				break;
			case 'Description':
				$value = wptexturize( $value );
				break;
			case 'Author':
				if ( $this->get( 'AuthorURI' ) ) {
					$value = sprintf( '<a href="%1$s">%2$s</a>', $this->display( 'AuthorURI', true, $translate ), $value );
				} elseif ( ! $value ) {
					$value = __( 'Anonymous' );
				}
				break;
			case 'Tags':
				static $comma = null;
				if ( ! isset( $comma ) ) {
					$comma = wp_get_list_item_separator();
				}
				$value = implode( $comma, $value );
				break;
			case 'ThemeURI':
			case 'AuthorURI':
				$value = esc_url( $value );
				break;
		}

		return $value;
	}

	/**
	 * Translates a theme header.
	 *
	 * @since 3.4.0
	 *
	 * @param string       $header Theme header. Name, Description, Author, Version, ThemeURI, AuthorURI, Status, Tags.
	 * @param string|array $value  Value to translate. An array for Tags header, string otherwise.
	 * @return string|array Translated value. An array for Tags header, string otherwise.
	 */
	private function translate_header( $header, $value ) {
		switch ( $header ) {
			case 'Name':
				// Cached for sorting reasons.
				if ( isset( $this->name_translated ) ) {
					return $this->name_translated;
				}

				// phpcs:ignore WordPress.WP.I18n.LowLevelTranslationFunction,WordPress.WP.I18n.NonSingularStringLiteralText,WordPress.WP.I18n.NonSingularStringLiteralDomain
				$this->name_translated = translate( $value, $this->get( 'TextDomain' ) );

				return $this->name_translated;
			case 'Tags':
				if ( empty( $value ) || ! function_exists( 'get_theme_feature_list' ) ) {
					return $value;
				}

				static $tags_list;
				if ( ! isset( $tags_list ) ) {
					$tags_list = array(
						// As of 4.6, deprecated tags which are only used to provide translation for older themes.
						'black'             => __( 'Black' ),
						'blue'              => __( 'Blue' ),
						'brown'             => __( 'Brown' ),
						'gray'              => __( 'Gray' ),
						'green'             => __( 'Green' ),
						'orange'            => __( 'Orange' ),
						'pink'              => __( 'Pink' ),
						'purple'            => __( 'Purple' ),
						'red'               => __( 'Red' ),
						'silver'            => __( 'Silver' ),
						'tan'               => __( 'Tan' ),
						'white'             => __( 'White' ),
						'yellow'            => __( 'Yellow' ),
						'dark'              => _x( 'Dark', 'color scheme' ),
						'light'             => _x( 'Light', 'color scheme' ),
						'fixed-layout'      => __( 'Fixed Layout' ),
						'fluid-layout'      => __( 'Fluid Layout' ),
						'responsive-layout' => __( 'Responsive Layout' ),
						'blavatar'          => __( 'Blavatar' ),
						'photoblogging'     => __( 'Photoblogging' ),
						'seasonal'          => __( 'Seasonal' ),
					);

					$feature_list = get_theme_feature_list( false ); // No API.

					foreach ( $feature_list as $tags ) {
						$tags_list += $tags;
					}
				}

				foreach ( $value as &$tag ) {
					if ( isset( $tags_list[ $tag ] ) ) {
						$tag = $tags_list[ $tag ];
					} elseif ( isset( self::$tag_map[ $tag ] ) ) {
						$tag = $tags_list[ self::$tag_map[ $tag ] ];
					}
				}

				return $value;

			default:
				// phpcs:ignore WordPress.WP.I18n.LowLevelTranslationFunction,WordPress.WP.I18n.NonSingularStringLiteralText,WordPress.WP.I18n.NonSingularStringLiteralDomain
				$value = translate( $value, $this->get( 'TextDomain' ) );
		}
		return $value;
	}

	/**
	 * Returns the directory name of the theme's "stylesheet" files, inside the theme root.
	 *
	 * In the case of a child theme, this is directory name of the child theme.
	 * Otherwise, get_stylesheet() is the same as get_template().
	 *
	 * @since 3.4.0
	 *
	 * @return string Stylesheet
	 */
	public function get_stylesheet() {
		return $this->stylesheet;
	}

	/**
	 * Returns the directory name of the theme's "template" files, inside the theme root.
	 *
	 * In the case of a child theme, this is the directory name of the parent theme.
	 * Otherwise, the get_template() is the same as get_stylesheet().
	 *
	 * @since 3.4.0
	 *
	 * @return string Template
	 */
	public function get_template() {
		return $this->template;
	}

	/**
	 * Returns the absolute path to the directory of a theme's "stylesheet" files.
	 *
	 * In the case of a child theme, this is the absolute path to the directory
	 * of the child theme's files.
	 *
	 * @since 3.4.0
	 *
	 * @return string Absolute path of the stylesheet directory.
	 */
	public function get_stylesheet_directory() {
		if ( $this->errors() && in_array( 'theme_root_missing', $this->errors()->get_error_codes(), true ) ) {
			return '';
		}

		return $this->theme_root . '/' . $this->stylesheet;
	}

	/**
	 * Returns the absolute path to the directory of a theme's "template" files.
	 *
	 * In the case of a child theme, this is the absolute path to the directory
	 * of the parent theme's files.
	 *
	 * @since 3.4.0
	 *
	 * @return string Absolute path of the template directory.
	 */
	public function get_template_directory() {
		if ( $this->parent() ) {
			$theme_root = $this->parent()->theme_root;
		} else {
			$theme_root = $this->theme_root;
		}

		return $theme_root . '/' . $this->template;
	}

	/**
	 * Returns the URL to the directory of a theme's "stylesheet" files.
	 *
	 * In the case of a child theme, this is the URL to the directory of the
	 * child theme's files.
	 *
	 * @since 3.4.0
	 *
	 * @return string URL to the stylesheet directory.
	 */
	public function get_stylesheet_directory_uri() {
		return $this->get_theme_root_uri() . '/' . str_replace( '%2F', '/', rawurlencode( $this->stylesheet ) );
	}

	/**
	 * Returns the URL to the directory of a theme's "template" files.
	 *
	 * In the case of a child theme, this is the URL to the directory of the
	 * parent theme's files.
	 *
	 * @since 3.4.0
	 *
	 * @return string URL to the template directory.
	 */
	public function get_template_directory_uri() {
		if ( $this->parent() ) {
			$theme_root_uri = $this->parent()->get_theme_root_uri();
		} else {
			$theme_root_uri = $this->get_theme_root_uri();
		}

		return $theme_root_uri . '/' . str_replace( '%2F', '/', rawurlencode( $this->template ) );
	}

	/**
	 * Returns the absolute path to the directory of the theme root.
	 *
	 * This is typically the absolute path to wp-content/themes.
	 *
	 * @since 3.4.0
	 *
	 * @return string Theme root.
	 */
	public function get_theme_root() {
		return $this->theme_root;
	}

	/**
	 * Returns the URL to the directory of the theme root.
	 *
	 * This is typically the absolute URL to wp-content/themes. This forms the basis
	 * for all other URLs returned by WP_Theme, so we pass it to the public function
	 * get_theme_root_uri() and allow it to run the {@see 'theme_root_uri'} filter.
	 *
	 * @since 3.4.0
	 *
	 * @return string Theme root URI.
	 */
	public function get_theme_root_uri() {
		if ( ! isset( $this->theme_root_uri ) ) {
			$this->theme_root_uri = get_theme_root_uri( $this->stylesheet, $this->theme_root );
		}
		return $this->theme_root_uri;
	}

	/**
	 * Returns the main screenshot file for the theme.
	 *
	 * The main screenshot is called screenshot.png. gif and jpg extensions are also allowed.
	 *
	 * Screenshots for a theme must be in the stylesheet directory. (In the case of child
	 * themes, parent theme screenshots are not inherited.)
	 *
	 * @since 3.4.0
	 *
	 * @param string $uri Type of URL to return, either 'relative' or an absolute URI. Defaults to absolute URI.
	 * @return string|false Screenshot file. False if the theme does not have a screenshot.
	 */
	public function get_screenshot( $uri = 'uri' ) {
		$screenshot = $this->cache_get( 'screenshot' );
		if ( $screenshot ) {
			if ( 'relative' === $uri ) {
				return $screenshot;
			}
			return $this->get_stylesheet_directory_uri() . '/' . $screenshot;
		} elseif ( 0 === $screenshot ) {
			return false;
		}

		foreach ( array( 'png', 'gif', 'jpg', 'jpeg', 'webp' ) as $ext ) {
			if ( file_exists( $this->get_stylesheet_directory() . "/screenshot.$ext" ) ) {
				$this->cache_add( 'screenshot', 'screenshot.' . $ext );
				if ( 'relative' === $uri ) {
					return 'screenshot.' . $ext;
				}
				return $this->get_stylesheet_directory_uri() . '/' . 'screenshot.' . $ext;
			}
		}

		$this->cache_add( 'screenshot', 0 );
		return false;
	}

	/**
	 * Returns files in the theme's directory.
	 *
	 * @since 3.4.0
	 *
	 * @param string[]|string $type          Optional. Array of extensions to find, string of a single extension,
	 *                                       or null for all extensions. Default null.
	 * @param int             $depth         Optional. How deep to search for files. Defaults to a flat scan (0 depth).
	 *                                       -1 depth is infinite.
	 * @param bool            $search_parent Optional. Whether to return parent files. Default false.
	 * @return string[] Array of files, keyed by the path to the file relative to the theme's directory, with the values
	 *                  being absolute paths.
	 */
	public function get_files( $type = null, $depth = 0, $search_parent = false ) {
		$files = (array) self::scandir( $this->get_stylesheet_directory(), $type, $depth );

		if ( $search_parent && $this->parent() ) {
			$files += (array) self::scandir( $this->get_template_directory(), $type, $depth );
		}

		return array_filter( $files );
	}

	/**
	 * Returns the theme's post templates.
	 *
	 * @since 4.7.0
	 * @since 5.8.0 Include block templates.
	 *
	 * @return array[] Array of page template arrays, keyed by post type and filename,
	 *                 with the value of the translated header name.
	 */
	public function get_post_templates() {
		// If you screw up your active theme and we invalidate your parent, most things still work. Let it slide.
		if ( $this->errors() && $this->errors()->get_error_codes() !== array( 'theme_parent_invalid' ) ) {
			return array();
		}

		$post_templates = $this->cache_get( 'post_templates' );

		if ( ! is_array( $post_templates ) ) {
			$post_templates = array();

			$files = (array) $this->get_files( 'php', 1, true );

			foreach ( $files as $file => $full_path ) {
				if ( ! preg_match( '|Template Name:(.*)$|mi', file_get_contents( $full_path ), $header ) ) {
					continue;
				}

				$types = array( 'page' );
				if ( preg_match( '|Template Post Type:(.*)$|mi', file_get_contents( $full_path ), $type ) ) {
					$types = explode( ',', _cleanup_header_comment( $type[1] ) );
				}

				foreach ( $types as $type ) {
					$type = sanitize_key( $type );
					if ( ! isset( $post_templates[ $type ] ) ) {
						$post_templates[ $type ] = array();
					}

					$post_templates[ $type ][ $file ] = _cleanup_header_comment( $header[1] );
				}
			}

			if ( current_theme_supports( 'block-templates' ) ) {
				$block_templates = get_block_templates( array(), 'wp_template' );
				foreach ( get_post_types( array( 'public' => true ) ) as $type ) {
					foreach ( $block_templates as $block_template ) {
						if ( ! $block_template->is_custom ) {
							continue;
						}

						if ( isset( $block_template->post_types ) && ! in_array( $type, $block_template->post_types, true ) ) {
							continue;
						}

						$post_templates[ $type ][ $block_template->slug ] = $block_template->title;
					}
				}
			}

			$this->cache_add( 'post_templates', $post_templates );
		}

		if ( $this->load_textdomain() ) {
			foreach ( $post_templates as &$post_type ) {
				foreach ( $post_type as &$post_template ) {
					$post_template = $this->translate_header( 'Template Name', $post_template );
				}
			}
		}

		return $post_templates;
	}

	/**
	 * Returns the theme's post templates for a given post type.
	 *
	 * @since 3.4.0
	 * @since 4.7.0 Added the `$post_type` parameter.
	 *
	 * @param WP_Post|null $post      Optional. The post being edited, provided for context.
	 * @param string       $post_type Optional. Post type to get the templates for. Default 'page'.
	 *                                If a post is provided, its post type is used.
	 * @return string[] Array of template header names keyed by the template file name.
	 */
	public function get_page_templates( $post = null, $post_type = 'page' ) {
		if ( $post ) {
			$post_type = get_post_type( $post );
		}

		$post_templates = $this->get_post_templates();
		$post_templates = isset( $post_templates[ $post_type ] ) ? $post_templates[ $post_type ] : array();

		/**
		 * Filters list of page templates for a theme.
		 *
		 * @since 4.9.6
		 *
		 * @param string[]     $post_templates Array of template header names keyed by the template file name.
		 * @param WP_Theme     $theme          The theme object.
		 * @param WP_Post|null $post           The post being edited, provided for context, or null.
		 * @param string       $post_type      Post type to get the templates for.
		 */
		$post_templates = (array) apply_filters( 'theme_templates', $post_templates, $this, $post, $post_type );

		/**
		 * Filters list of page templates for a theme.
		 *
		 * The dynamic portion of the hook name, `$post_type`, refers to the post type.
		 *
		 * Possible hook names include:
		 *
		 *  - `theme_post_templates`
		 *  - `theme_page_templates`
		 *  - `theme_attachment_templates`
		 *
		 * @since 3.9.0
		 * @since 4.4.0 Converted to allow complete control over the `$page_templates` array.
		 * @since 4.7.0 Added the `$post_type` parameter.
		 *
		 * @param string[]     $post_templates Array of template header names keyed by the template file name.
		 * @param WP_Theme     $theme          The theme object.
		 * @param WP_Post|null $post           The post being edited, provided for context, or null.
		 * @param string       $post_type      Post type to get the templates for.
		 */
		$post_templates = (array) apply_filters( "theme_{$post_type}_templates", $post_templates, $this, $post, $post_type );

		return $post_templates;
	}

	/**
	 * Scans a directory for files of a certain extension.
	 *
	 * @since 3.4.0
	 *
	 * @param string            $path          Absolute path to search.
	 * @param array|string|null $extensions    Optional. Array of extensions to find, string of a single extension,
	 *                                         or null for all extensions. Default null.
	 * @param int               $depth         Optional. How many levels deep to search for files. Accepts 0, 1+, or
	 *                                         -1 (infinite depth). Default 0.
	 * @param string            $relative_path Optional. The basename of the absolute path. Used to control the
	 *                                         returned path for the found files, particularly when this function
	 *                                         recurses to lower depths. Default empty.
	 * @return string[]|false Array of files, keyed by the path to the file relative to the `$path` directory prepended
	 *                        with `$relative_path`, with the values being absolute paths. False otherwise.
	 */
	private static function scandir( $path, $extensions = null, $depth = 0, $relative_path = '' ) {
		if ( ! is_dir( $path ) ) {
			return false;
		}

		if ( $extensions ) {
			$extensions  = (array) $extensions;
			$_extensions = implode( '|', $extensions );
		}

		$relative_path = trailingslashit( $relative_path );
		if ( '/' === $relative_path ) {
			$relative_path = '';
		}

		$results = scandir( $path );
		$files   = array();

		/**
		 * Filters the array of excluded directories and files while scanning theme folder.
		 *
		 * @since 4.7.4
		 *
		 * @param string[] $exclusions Array of excluded directories and files.
		 */
		$exclusions = (array) apply_filters( 'theme_scandir_exclusions', array( 'CVS', 'node_modules', 'vendor', 'bower_components' ) );

		foreach ( $results as $result ) {
			if ( '.' === $result[0] || in_array( $result, $exclusions, true ) ) {
				continue;
			}
			if ( is_dir( $path . '/' . $result ) ) {
				if ( ! $depth ) {
					continue;
				}
				$found = self::scandir( $path . '/' . $result, $extensions, $depth - 1, $relative_path . $result );
				$files = array_merge_recursive( $files, $found );
			} elseif ( ! $extensions || preg_match( '~\.(' . $_extensions . ')$~', $result ) ) {
				$files[ $relative_path . $result ] = $path . '/' . $result;
			}
		}

		return $files;
	}

	/**
	 * Loads the theme's textdomain.
	 *
	 * Translation files are not inherited from the parent theme. TODO: If this fails for the
	 * child theme, it should probably try to load the parent theme's translations.
	 *
	 * @since 3.4.0
	 *
	 * @return bool True if the textdomain was successfully loaded or has already been loaded.
	 *  False if no textdomain was specified in the file headers, or if the domain could not be loaded.
	 */
	public function load_textdomain() {
		if ( isset( $this->textdomain_loaded ) ) {
			return $this->textdomain_loaded;
		}

		$textdomain = $this->get( 'TextDomain' );
		if ( ! $textdomain ) {
			$this->textdomain_loaded = false;
			return false;
		}

		if ( is_textdomain_loaded( $textdomain ) ) {
			$this->textdomain_loaded = true;
			return true;
		}

		$path       = $this->get_stylesheet_directory();
		$domainpath = $this->get( 'DomainPath' );
		if ( $domainpath ) {
			$path .= $domainpath;
		} else {
			$path .= '/languages';
		}

		$this->textdomain_loaded = load_theme_textdomain( $textdomain, $path );
		return $this->textdomain_loaded;
	}

	/**
	 * Determines whether the theme is allowed (multisite only).
	 *
	 * @since 3.4.0
	 *
	 * @param string $check   Optional. Whether to check only the 'network'-wide settings, the 'site'
	 *                        settings, or 'both'. Defaults to 'both'.
	 * @param int    $blog_id Optional. Ignored if only network-wide settings are checked. Defaults to current site.
	 * @return bool Whether the theme is allowed for the network. Returns true in single-site.
	 */
	public function is_allowed( $check = 'both', $blog_id = null ) {
		if ( ! is_multisite() ) {
			return true;
		}

		if ( 'both' === $check || 'network' === $check ) {
			$allowed = self::get_allowed_on_network();
			if ( ! empty( $allowed[ $this->get_stylesheet() ] ) ) {
				return true;
			}
		}

		if ( 'both' === $check || 'site' === $check ) {
			$allowed = self::get_allowed_on_site( $blog_id );
			if ( ! empty( $allowed[ $this->get_stylesheet() ] ) ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * Returns whether this theme is a block-based theme or not.
	 *
	 * @since 5.9.0
	 *
	 * @return bool
	 */
	public function is_block_theme() {
		$paths_to_index_block_template = array(
			$this->get_file_path( '/block-templates/index.html' ),
			$this->get_file_path( '/templates/index.html' ),
		);

		foreach ( $paths_to_index_block_template as $path_to_index_block_template ) {
			if ( is_file( $path_to_index_block_template ) && is_readable( $path_to_index_block_template ) ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * Retrieves the path of a file in the theme.
	 *
	 * Searches in the stylesheet directory before the template directory so themes
	 * which inherit from a parent theme can just override one file.
	 *
	 * @since 5.9.0
	 *
	 * @param string $file Optional. File to search for in the stylesheet directory.
	 * @return string The path of the file.
	 */
	public function get_file_path( $file = '' ) {
		$file = ltrim( $file, '/' );

		$stylesheet_directory = $this->get_stylesheet_directory();
		$template_directory   = $this->get_template_directory();

		if ( empty( $file ) ) {
			$path = $stylesheet_directory;
		} elseif ( file_exists( $stylesheet_directory . '/' . $file ) ) {
			$path = $stylesheet_directory . '/' . $file;
		} else {
			$path = $template_directory . '/' . $file;
		}

		/** This filter is documented in wp-includes/link-template.php */
		return apply_filters( 'theme_file_path', $path, $file );
	}

	/**
	 * Determines the latest WordPress default theme that is installed.
	 *
	 * This hits the filesystem.
	 *
	 * @since 4.4.0
	 *
	 * @return WP_Theme|false Object, or false if no theme is installed, which would be bad.
	 */
	public static function get_core_default_theme() {
		foreach ( array_reverse( self::$default_themes ) as $slug => $name ) {
			$theme = wp_get_theme( $slug );
			if ( $theme->exists() ) {
				return $theme;
			}
		}
		return false;
	}

	/**
	 * Returns array of stylesheet names of themes allowed on the site or network.
	 *
	 * @since 3.4.0
	 *
	 * @param int $blog_id Optional. ID of the site. Defaults to the current site.
	 * @return string[] Array of stylesheet names.
	 */
	public static function get_allowed( $blog_id = null ) {
		/**
		 * Filters the array of themes allowed on the network.
		 *
		 * Site is provided as context so that a list of network allowed themes can
		 * be filtered further.
		 *
		 * @since 4.5.0
		 *
		 * @param string[] $allowed_themes An array of theme stylesheet names.
		 * @param int      $blog_id        ID of the site.
		 */
		$network = (array) apply_filters( 'network_allowed_themes', self::get_allowed_on_network(), $blog_id );
		return $network + self::get_allowed_on_site( $blog_id );
	}

	/**
	 * Returns array of stylesheet names of themes allowed on the network.
	 *
	 * @since 3.4.0
	 *
	 * @return string[] Array of stylesheet names.
	 */
	public static function get_allowed_on_network() {
		static $allowed_themes;
		if ( ! isset( $allowed_themes ) ) {
			$allowed_themes = (array) get_site_option( 'allowedthemes' );
		}

		/**
		 * Filters the array of themes allowed on the network.
		 *
		 * @since MU (3.0.0)
		 *
		 * @param string[] $allowed_themes An array of theme stylesheet names.
		 */
		$allowed_themes = apply_filters( 'allowed_themes', $allowed_themes );

		return $allowed_themes;
	}

	/**
	 * Returns array of stylesheet names of themes allowed on the site.
	 *
	 * @since 3.4.0
	 *
	 * @param int $blog_id Optional. ID of the site. Defaults to the current site.
	 * @return string[] Array of stylesheet names.
	 */
	public static function get_allowed_on_site( $blog_id = null ) {
		static $allowed_themes = array();

		if ( ! $blog_id || ! is_multisite() ) {
			$blog_id = get_current_blog_id();
		}

		if ( isset( $allowed_themes[ $blog_id ] ) ) {
			/**
			 * Filters the array of themes allowed on the site.
			 *
			 * @since 4.5.0
			 *
			 * @param string[] $allowed_themes An array of theme stylesheet names.
			 * @param int      $blog_id        ID of the site. Defaults to current site.
			 */
			return (array) apply_filters( 'site_allowed_themes', $allowed_themes[ $blog_id ], $blog_id );
		}

		$current = get_current_blog_id() == $blog_id;

		if ( $current ) {
			$allowed_themes[ $blog_id ] = get_option( 'allowedthemes' );
		} else {
			switch_to_blog( $blog_id );
			$allowed_themes[ $blog_id ] = get_option( 'allowedthemes' );
			restore_current_blog();
		}

		// This is all super old MU back compat joy.
		// 'allowedthemes' keys things by stylesheet. 'allowed_themes' keyed things by name.
		if ( false === $allowed_themes[ $blog_id ] ) {
			if ( $current ) {
				$allowed_themes[ $blog_id ] = get_option( 'allowed_themes' );
			} else {
				switch_to_blog( $blog_id );
				$allowed_themes[ $blog_id ] = get_option( 'allowed_themes' );
				restore_current_blog();
			}

			if ( ! is_array( $allowed_themes[ $blog_id ] ) || empty( $allowed_themes[ $blog_id ] ) ) {
				$allowed_themes[ $blog_id ] = array();
			} else {
				$converted = array();
				$themes    = wp_get_themes();
				foreach ( $themes as $stylesheet => $theme_data ) {
					if ( isset( $allowed_themes[ $blog_id ][ $theme_data->get( 'Name' ) ] ) ) {
						$converted[ $stylesheet ] = true;
					}
				}
				$allowed_themes[ $blog_id ] = $converted;
			}
			// Set the option so we never have to go through this pain again.
			if ( is_admin() && $allowed_themes[ $blog_id ] ) {
				if ( $current ) {
					update_option( 'allowedthemes', $allowed_themes[ $blog_id ] );
					delete_option( 'allowed_themes' );
				} else {
					switch_to_blog( $blog_id );
					update_option( 'allowedthemes', $allowed_themes[ $blog_id ] );
					delete_option( 'allowed_themes' );
					restore_current_blog();
				}
			}
		}

		/** This filter is documented in wp-includes/class-wp-theme.php */
		return (array) apply_filters( 'site_allowed_themes', $allowed_themes[ $blog_id ], $blog_id );
	}

	/**
	 * Enables a theme for all sites on the current network.
	 *
	 * @since 4.6.0
	 *
	 * @param string|string[] $stylesheets Stylesheet name or array of stylesheet names.
	 */
	public static function network_enable_theme( $stylesheets ) {
		if ( ! is_multisite() ) {
			return;
		}

		if ( ! is_array( $stylesheets ) ) {
			$stylesheets = array( $stylesheets );
		}

		$allowed_themes = get_site_option( 'allowedthemes' );
		foreach ( $stylesheets as $stylesheet ) {
			$allowed_themes[ $stylesheet ] = true;
		}

		update_site_option( 'allowedthemes', $allowed_themes );
	}

	/**
	 * Disables a theme for all sites on the current network.
	 *
	 * @since 4.6.0
	 *
	 * @param string|string[] $stylesheets Stylesheet name or array of stylesheet names.
	 */
	public static function network_disable_theme( $stylesheets ) {
		if ( ! is_multisite() ) {
			return;
		}

		if ( ! is_array( $stylesheets ) ) {
			$stylesheets = array( $stylesheets );
		}

		$allowed_themes = get_site_option( 'allowedthemes' );
		foreach ( $stylesheets as $stylesheet ) {
			if ( isset( $allowed_themes[ $stylesheet ] ) ) {
				unset( $allowed_themes[ $stylesheet ] );
			}
		}

		update_site_option( 'allowedthemes', $allowed_themes );
	}

	/**
	 * Sorts themes by name.
	 *
	 * @since 3.4.0
	 *
	 * @param WP_Theme[] $themes Array of theme objects to sort (passed by reference).
	 */
	public static function sort_by_name( &$themes ) {
		if ( 0 === strpos( get_user_locale(), 'en_' ) ) {
			uasort( $themes, array( 'WP_Theme', '_name_sort' ) );
		} else {
			foreach ( $themes as $key => $theme ) {
				$theme->translate_header( 'Name', $theme->headers['Name'] );
			}
			uasort( $themes, array( 'WP_Theme', '_name_sort_i18n' ) );
		}
	}

	/**
	 * Callback function for usort() to naturally sort themes by name.
	 *
	 * Accesses the Name header directly from the class for maximum speed.
	 * Would choke on HTML but we don't care enough to slow it down with strip_tags().
	 *
	 * @since 3.4.0
	 *
	 * @param WP_Theme $a First theme.
	 * @param WP_Theme $b Second theme.
	 * @return int Negative if `$a` falls lower in the natural order than `$b`. Zero if they fall equally.
	 *             Greater than 0 if `$a` falls higher in the natural order than `$b`. Used with usort().
	 */
	private static function _name_sort( $a, $b ) {
		return strnatcasecmp( $a->headers['Name'], $b->headers['Name'] );
	}

	/**
	 * Callback function for usort() to naturally sort themes by translated name.
	 *
	 * @since 3.4.0
	 *
	 * @param WP_Theme $a First theme.
	 * @param WP_Theme $b Second theme.
	 * @return int Negative if `$a` falls lower in the natural order than `$b`. Zero if they fall equally.
	 *             Greater than 0 if `$a` falls higher in the natural order than `$b`. Used with usort().
	 */
	private static function _name_sort_i18n( $a, $b ) {
		return strnatcasecmp( $a->name_translated, $b->name_translated );
	}

	private static function _check_headers_property_has_correct_type( $headers ) {
		if ( ! is_array( $headers ) ) {
			return false;
		}
		foreach ( $headers as $key => $value ) {
			if ( ! is_string( $key ) || ! is_string( $value ) ) {
				return false;
			}
		}
		return true;
	}
}