Hi HuiSheng,
I think it comes from jBPM v3. There is support for hierahical names support on transitions.
Here are some useful links that can put some light on it:
https://jira.jboss.org/browse/GPD-20
http://docs.jboss.org/jbpm/v3/userguide/processmodelling.html#hierarchicalnames
I am not sure if that is valid for 4.x. I made a quick test and that worked fine for a very simple case.