The difference with a normal push, is that the operation does does not own the set element, but only contains the label of the set. The SetManager will match the set label with the actual element. [It is much like containing a pointer, and the SetManager deals with dereference].
SetManager acts similar to VarRW [almost like a symbol-table].
| PushSet (const string& setid)
|setid||name of the set.|
| INSTR_VISITABLE ()
|const string& setid ()
Returns: name of the set.