wp_filter_content_tags() WordPress Function

function wp_filter_content_tags( $content, $context = null ) {
	if ( null === $context ) {
		$context = current_filter();
	}

	$add_img_loading_attr    = wp_lazy_loading_enabled( 'img', $context );
	$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 && false === strpos( $filtered_image, ' width=' ) && false === strpos( $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 && false === strpos( $filtered_image, ' srcset=' ) ) {
				$filtered_image = wp_img_tag_add_srcset_and_sizes_attr( $filtered_image, $context, $attachment_id );
			}

			// Add 'loading' attribute if applicable.
			if ( $add_img_loading_attr && false === strpos( $filtered_image, ' loading=' ) ) {
				$filtered_image = wp_img_tag_add_loading_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] ] );
		}

		// Filter an iframe match.
		if ( isset( $iframes[ $match[0] ] ) ) {
			$filtered_iframe = $match[0];

			// Add 'loading' attribute if applicable.
			if ( $add_iframe_loading_attr && false === strpos( $filtered_iframe, ' loading=' ) ) {
				$filtered_iframe = wp_iframe_tag_add_loading_attr( $filtered_iframe, $context );
			}

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

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

	return $content;
}