Questions About v$enqueue_lock

Hi DBAs:

Today I resolved an RMAN problem using the query below. I found it in Note 1018679.102, but it is also in a few other places:

SELECT s.inst_id, l.id1, l.id2, s.sid, username AS "User", program, l.type, module, action, logon_time "Logon", l.*
  FROM v$session s,v$enqueue_lock l
WHERE l.sid = s.sid and l.type = 'CF'
AND l.id1 = 0 and l.id2 = 2;

I am updating my notes and would like to better understand what v$enqueue_lock.ID1 and v$enqueue_lock.ID2 mean.  The documentation I have found repeats:

ID1 NUMBER Lock identifier #1 (depends on type)