Description

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.

Usage

$string = wp_filter_content_tags( $content, $context );

Parameters

$content

( string ) required – The HTML content to be filtered.

$context

( string ) optional – Optional. Additional context to pass to the filters. Defaults to current_filter() when not set.

Returns

string Converted content with images modified.

Source

File name: wordpress/wp-includes/media.php
Lines:

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 );

      // Add 'decoding=async' attribute unless a 'decoding' attribute is already present.
      if ( ! str_contains( $filtered_image, ' decoding=' ) ) {
        $filtered_image = wp_img_tag_add_decoding_attr( $filtered_image, $context );
      }

      
/**
 * 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.
 */
      $filtered_image = apply_filters( 'wp_content_img_tag', $filtered_image, $context, $attachment_id );

      if ( $filtered_image !== $match[0] ) {
        $content = str_replace( $match[0], $filtered_image, $content );
      }

      /*
			 * Unset image lookup to not run the same logic again unnecessarily if the same image tag is used more than
			 * once in the same blob of content.
			 */
      unset( $images[ $match[0] ] );
    }

 

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