TheOptimizationIdiot - 5:44 am on Apr 14, 2013 (gmt 0)
That is not the only thing a colon is used for.
forum: subforum: thread for example.
So, forum: is not further defined (repeatedly) by subforum and subforum: is not further defined (repeatedly) by thread? I think you just said exactly what I did with different words, otherwise I'm completely misunderstanding what you mean by forum: subforum: thread.
I would think forum: subforum: thread is likely a fairly good example of "phrase/thing", defined by "subphrase/subthing", and subphrase/subthing: defined by "specific phrase/specific thing".
Another way of looking at it would be:
(Did I use a : out of habit? lol)
Broad: More Specific: Very Specific
Very specific is a part of (defines) more specific, which is a part of (defines) broad.