I've been looking at this for a while now, but I just can't seem to understand (maybe it's because I'm still a beginner at PHP). On the PhpBB development wiki, there's a page "Displaying posts and topics on external pages" and the part where it says "By leaving the array "$forum_id" empty, it will mean there are no restrictions and it will take the latest posts/topics from the entire forum instead of any particular area." but the array (to me) is not empty since it has numbers.
$search_limit = 5;
$forum_id = array(2, 5);
$forum_id_where = create_where_clauses($forum_id, 'forum');
$topic_id = array(20, 50);
$topic_id_where = create_where_clauses($topic_id, 'topic');