[MlMt] Subrules - what is the purpose

[Antonio Leding]

MM crew - what is the purpose of a subrule?  Are these just for grouping 
(i.e. no selection criteria or actions) or are there other purposes?

I thought they might also be used to setup a hierarchy of rule execution 
but after testing this a bit, I find this is not the case.  The behavior 
I see is that even if the parent rule has messages that meet the 
selection criteria, the subrules still do not execute…