This is confusing me

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');

[COLOR=#000000]$forum_id = array(2, 5[COLOR=#007700]);

display posts and topics from forums 2 and 5 only

[/COLOR][/COLOR]$forum_id = array(); [COLOR=#000000][COLOR=#007700]

display posts and topics from all forums.

Oh, I’m so stupid, how could I have not realized the numbers were the actual forum id face palm but thanks for the help!