I'm using the WordPress gallery to display a thumbnail group of images. I want to be able to use jQuery in order to add data-fancybox="whatever" immediately after the <a> tag like this:

<a data-fancybox="whatever" href="https://google.com"</a>

The existing way the links are set up are like this:

 <dt class="gallery-icon landscape">
    <a href="http://" class="attachment-thumbnail size-thumbnail" ></a>


What I would like to do, is add the data-fancybox="group" to the <a> tag that lives on the wp_attachment links for gallery, like this:

<dt class="gallery-icon landscape">
    <a data-fancybox="group" href="http://" class="attachment-thumbnail size-thumbnail" ></a>

Does anyone know how I can do that? I would greatly appreciate any help - if I can clarify, please let me know.

Thanks Mike


This solution will add the data-fancybox="group" to gallery links produced by the default [gallery] shortcode. This has been tested and works regardless of whether themes have HTML5 theme support enabled for galleries or not.

The solution works by using the post_gallery filter to gain access to the gallery shortcode's output. From there, the HTML is parsed and manipulated using PHP's DOMDocument() and DOMXpath().

add_filter( 'post_gallery', 'wpse_gallery_shortcode', 10, 3 );
 * Filters the default gallery shortcode output.
 * @see gallery_shortcode()
 * @param string $output   The gallery output. Default empty.
 * @param array  $attr     Attributes of the gallery shortcode.
 * @param int    $instance Unique numeric ID of this gallery shortcode instance.
function wpse_gallery_shortcode( $output, $attr, $instance ) {
    // Temporarily remove our filter to prevent infinite loop.
    remove_filter( 'post_gallery', 'wpse_gallery_shortcode', 10, 3 );

    // Use WordPress' native function for generating gallery output.
    $gallery_html = gallery_shortcode( $attr );

    // Create an instance of DOMDocument.
    $dom = new \DOMDocument();

    // Supress errors due to malformed HTML.
    // See http://stackoverflow.com/a/17559716/3059883
    $libxml_previous_state = libxml_use_internal_errors( true );

    // Populate $dom with $gallery_html, making sure to handle UTF-8, otherwise
    // problems will occur with UTF-8 characters.
    // Also, make sure that the doctype and HTML tags are not added to our HTML fragment. http://stackoverflow.com/a/22490902/3059883
    $dom->loadHTML( mb_convert_encoding( $gallery_html, 'HTML-ENTITIES', 'UTF-8' ), LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD );

    // Restore previous state of libxml_use_internal_errors() now that we're done.
    // Again, see http://stackoverflow.com/a/17559716/3059883
    libxml_use_internal_errors( $libxml_previous_state );

    // Create an instance of DOMXpath.
    $xpath = new \DOMXpath( $dom );

    // Match elements with the class gallery-icon (these can be <div> or <dt> depending on whether the theme has support for HTML5.
    // See http://stackoverflow.com/a/26126336/3059883
    $gallery_icons = $xpath->query( "//*[contains(concat(' ', normalize-space(@class), ' '), ' gallery-icon ')]" );

    // Iterate over the the gallery icons.
    foreach ( $gallery_icons as $gallery_icon ) {
        // Find the <a> tags and add our custom attribute and value.
        $gallery_icon_child_node_link = $xpath->query( "//a", $gallery_icon );
        foreach ( $gallery_icon_child_node_link as $node_link ) {
            $gallery_icon_data_fancy_box = $dom->createAttribute( 'data-fancybox' );
            $gallery_icon_data_fancy_box->value = 'group';

            $node_link->appendChild( $gallery_icon_data_fancy_box );                

    // Save the updated HTML.
    $gallery_html = $dom->saveHTML();   

    // Add our filter back so that it will run the next time that the gallery shortcode is used.
    add_filter( 'post_gallery', 'wpse_gallery_shortcode', 10, 3 );

    // Return the modified HTML.
    return $gallery_html;

This code is a bit verbose, mostly because it addresses a bunch of gothcas with DOMDocument().

You might also consider adapting the answers to these similar questions:

  • 1
    Holy $H!_, that worked! Thanks so much for your help! I added the function and it works like a charm for my gallery pages! I REALLY appreciate your help. – Mixmastermichael May 8 '17 at 15:32
  • Woohoo! Happy to help, @Mixmastermichael! – Dave Romsey May 8 '17 at 17:15

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