Wordpress ACF Custom location rule : Descendant of Page

##About ACF is a wonderful plugin for Wordpress to get the most out of the custom fields. Basic location rules are not always sufficient to target the right page being edited. Basic rule "Parent page" only targets the descending pages of first level, meaning the children's pages will not be targeted.

This custom rule will target every pages from every levels that is a descendant of the specified page.

##Requirements

• Wordpress 3.8+
• Advanced Custom Fields 3.5.7+

##Setup Just copy/paste the following code inside your theme's functions.php and the custom rule will appear in your ACF form.

add_filter('acf/location/rule_types', 'acf_location_rules_types');
function acf_location_rules_types( $choices ) {
    $choices['Page']['descendantof'] = 'Descendant of the page';
    return $choices;
}
add_filter('acf/location/rule_values/descendantof', 'acf_location_rules_values_descendantof');
function acf_location_rules_values_descendantof( $choices ) {
    foreach(get_pages() as $p)
        $choices[ $p->ID ] = $p->post_title;
    return $choices;
}
add_filter('acf/location/rule_match/descendantof', 'acf_location_rules_match_descendantof', 10, 3);
function acf_location_rules_match_descendantof( $match, $rule, $options ) {
    global $post;
    $match = false;
    $selectedPageID = (int) $rule['value'];
 
    foreach(get_post_ancestors( $post->ID ) as $ancestor) {
      if($ancestor == $selectedPageID)
        $match = true;
    }
    if($rule['operator'] == "==")
      return $match;
    elseif($rule['operator'] == "!=")
      return !$match;
}