wp_filter_content_tags( string $content, string $context = null ): string

Source

	 * Filters whether to add the `loading` attribute to the specified tag in the specified context.
	 *
	 * @since 5.5.0
	 *
	 * @param bool   $default  Default value.
	 * @param string $tag_name The tag name.
	 * @param string $context  Additional context, like the current filter name
	 *                         or the function name from where this was called.
	 */
	return (bool) apply_filters( 'wp_lazy_loading_enabled', $default, $tag_name, $context );
}

/**
 * Filters specific tags in post content and modifies their markup.
 *
 * Modifies HTML tags in post content to include new browser and HTML technologies
 * that may not have existed at the time of post creation. These modifications currently
 * include adding `srcset`, `sizes`, and `loading` attributes to `img` HTML tags, as well
 * as adding `loading` attributes to `iframe` HTML tags.
 * Future similar optimizations should be added/expected here.
 *
 * @since 5.5.0
 * @since 5.7.0 Now supports adding `loading` attributes to `iframe` tags.
 *
 * @see wp_img_tag_add_width_and_height_attr()
 * @see wp_img_tag_add_srcset_and_sizes_attr()
 * @see wp_img_tag_add_loading_optimization_attrs()
 * @see wp_iframe_tag_add_loading_attr()
 *
 * @param string $content The HTML content to be filtered.
 * @param string $context Optional. Additional context to pass to the filters.
 *                        Defaults to `current_filter()` when not set.
 * @return string Converted content with images modified.
 */
function wp_filter_content_tags( $content, $context = null ) {
	if ( null === $context ) {
		$context = current_filter();
	}

	$add_iframe_loading_attr = wp_lazy_loading_enabled( 'iframe', $context );

	if ( ! preg_match_all( '/<(img|iframe)\s[^>]+>/', $content, $matches, PREG_SET_ORDER ) ) {
		return $content;
	}

	// List of the unique `img` tags found in $content.
	$images = array();

	// List of the unique `iframe` tags found in $content.
	$iframes = array();

	foreach ( $matches as $match ) {
		list( $tag, $tag_name ) = $match;

		switch ( $tag_name ) {
			case 'img':
				if ( preg_match( '/wp-image-([0-9]+)/i', $tag, $class_id ) ) {
					$attachment_id = absint( $class_id[1] );

					if ( $attachment_id ) {
						/*
						 * If exactly the same image tag is used more than once, overwrite it.
						 * All identical tags will be replaced later with 'str_replace()'.
						 */
						$images[ $tag ] = $attachment_id;
						break;
					}
				}
				$images[ $tag ] = 0;
				break;
			case 'iframe':
				$iframes[ $tag ] = 0;
				break;
		}
	}

	// Reduce the array to unique attachment IDs.
	$attachment_ids = array_unique( array_filter( array_values( $images ) ) );

	if ( count( $attachment_ids ) > 1 ) {
		/*
		 * Warm the object cache with post and meta information for all found
		 * images to avoid making individual database calls.
		 */
		_prime_post_caches( $attachment_ids, false, true );
	}

	// Iterate through the matches in order of occurrence as it is relevant for whether or not to lazy-load.
	foreach ( $matches as $match ) {
		// Filter an image match.
		if ( isset( $images[ $match[0] ] ) ) {
			$filtered_image = $match[0];
			$attachment_id  = $images[ $match[0] ];

			// Add 'width' and 'height' attributes if applicable.
			if ( $attachment_id > 0 && ! str_contains( $filtered_image, ' width=' ) && ! str_contains( $filtered_image, ' height=' ) ) {
				$filtered_image = wp_img_tag_add_width_and_height_attr( $filtered_image, $context, $attachment_id );
			}

			// Add 'srcset' and 'sizes' attributes if applicable.
			if ( $attachment_id > 0 && ! str_contains( $filtered_image, ' srcset=' ) ) {
				$filtered_image = wp_img_tag_add_srcset_and_sizes_attr( $filtered_image, $context, $attachment_id );
			}

			// Add loading optimization attributes if applicable.
			$filtered_image = wp_img_tag_add_loading_optimization_attrs( $filtered_image, $context );

			// Adds 'auto' to the sizes attribute if applicable.
			$filtered_image = wp_img_tag_add_auto_sizes( $filtered_image );

			/**
			 * Filters an img tag within the content for a given context.
			 *
			 * @since 6.0.0
			 *
			 * @param string $filtered_image Full img tag with attributes that will replace the source img tag.
			 * @param string $context        Additional context, like the current filter name or the function name from where this was called.
			 * @param int    $attachment_id  The image attachment ID. May be 0 in case the image is not an attachment.

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