While there is no option to limit the results pool to posts with specific parents only, it is possible with a filter, very easily.
What is this, and where do I put this custom code?
add_filter( 'asp_query_args', 'asp_include_only_parent_ids', 10, 2 );function asp_include_only_parent_ids( $args, $id ) {/*** Enter the post/cpt prent IDs here. The results will be* limited to objects with these parent IDs.*/$ids = array(1, 2, 3, 4, 5, 6);// -- !! Do not change anything below this line !! --$args['post_parent'] = $ids;return $args;}
..same code, but to apply only for specific search instances:
add_filter( 'asp_query_args', 'asp_include_only_parent_ids', 10, 2 );function asp_include_only_parent_ids( $args, $id ) {/*** Enter the post/cpt prent IDs here. The results will be* limited to objects with these parent IDs.*/$ids = array(1, 2, 3, 4, 5, 6);/*** Search instance IDs you want this code to apply on.*/$search_ids = array(1, 2);// --------------------------------------------------// --------------------------------------------------// -- !! Do not change anything below this line !! --// --------------------------------------------------if ( in_array($id, $search_ids) )$args['post_parent'] = $ids;return $args;}