GWP_series_box_template filter
a part of GWP tutorial : https://generatewp.com/group-post-series-custom-taxonomy
add_filter('GWP_series_box_template', function ( $template ){ return ' <div id="post-series"> <div class="series-title">Post Series: <a href="{series_url}" title="View all post in the series">{series_title}</a></div> {series_list} </div>'; });