Tagset 133281 is a new feature whose purpose is to allow the DataMixingModule to mix premixed pileup that is stored as raw data was queued as
The C++ changes in that tagset are also needed for this feature, but are much more general than that.  What the C++ changes really do is to give the DataMixingModule the ability to run producers (or filters) on demand in the secondary event (the event read by the secondary input source).
The (regular) MixingModule could have easily been given the same capability in that tagset with trivial additions to the C++ code in SimGeneral/MixingModule, but that would have introduced an undesirable dependency on unrelated changes.  The unrelated changes have now been approved in 6_2_X, so this tagset is those minor additions to the mixing module.

--- Tagset history ---
2013-06-26 00:51:21 - Queued by wmtan.