wp_preload_resources()

3751function wp_preload_resources() {3752	/**3753	 * Filters domains and URLs for resource preloads.3754	 *3755	 * @since 6.1.03756	 * @since 6.6.0 Added the `$fetchpriority` attribute.3757	 *3758	 * @param array  $preload_resources {3759	 *     Array of resources and their attributes, or URLs to print for resource preloads.3760	 *3761	 *     @type array ...$0 {3762	 *         Array of resource attributes.3763	 *3764	 *         @type string $href          URL to include in resource preloads. Required.3765	 *         @type string $as            How the browser should treat the resource3766	 *                                     (`script`, `style`, `image`, `document`, etc).3767	 *         @type string $crossorigin   Indicates the CORS policy of the specified resource.3768	 *         @type string $type          Type of the resource (`text/html`, `text/css`, etc).3769	 *         @type string $media         Accepts media types or media queries. Allows responsive preloading.3770	 *         @type string $imagesizes    Responsive source size to the source Set.3771	 *         @type string $imagesrcset   Responsive image sources to the source set.3772	 *         @type string $fetchpriority Fetchpriority value for the resource.3773	 *     }3774	 * }3775	 */3776	$preload_resources = apply_filters( 'wp_preload_resources', array() );3777 3778	if ( ! is_array( $preload_resources ) ) {3779		return;3780	}3781 3782	$unique_resources = array();3783 3784	// Parse the complete resource list and extract unique resources.3785	foreach ( $preload_resources as $resource ) {3786		if ( ! is_array( $resource ) ) {3787			continue;3788		}3789 3790		$attributes = $resource;3791		if ( isset( $resource['href'] ) ) {3792			$href = $resource['href'];3793			if ( isset( $unique_resources[ $href ] ) ) {3794				continue;3795			}3796			$unique_resources[ $href ] = $attributes;3797			// Media can use imagesrcset and not href.3798		} elseif ( ( 'image' === $resource['as'] ) &&3799			( isset( $resource['imagesrcset'] ) || isset( $resource['imagesizes'] ) )3800		) {3801			if ( isset( $unique_resources[ $resource['imagesrcset'] ] ) ) {3802				continue;3803			}3804			$unique_resources[ $resource['imagesrcset'] ] = $attributes;3805		} else {3806			continue;3807		}3808	}3809 3810	// Build and output the HTML for each unique resource.3811	foreach ( $unique_resources as $unique_resource ) {3812		$html = '';3813 3814		foreach ( $unique_resource as $resource_key => $resource_value ) {3815			if ( ! is_scalar( $resource_value ) ) {3816				continue;3817			}3818 3819			// Ignore non-supported attributes.3820			$non_supported_attributes = array( 'as', 'crossorigin', 'href', 'imagesrcset', 'imagesizes', 'type', 'media', 'fetchpriority' );3821			if ( ! in_array( $resource_key, $non_supported_attributes, true ) && ! is_numeric( $resource_key ) ) {3822				continue;3823			}3824 3825			// imagesrcset only usable when preloading image, ignore otherwise.3826			if ( ( 'imagesrcset' === $resource_key ) && ( ! isset( $unique_resource['as'] ) || ( 'image' !== $unique_resource['as'] ) ) ) {3827				continue;3828			}3829 3830			// imagesizes only usable when preloading image and imagesrcset present, ignore otherwise.