How to use implement drill-down in mxGraph?

i am using JGraph for a project. I am facing a big problem and the documentation of mxGr开发者_运维问答aph (java version) is not helping me. I would like to implement the drill-down functionality but i don't know how. Can somebody describe me how to do it?

mxGraph.enterGroup(Object) and mxGraph.exitGroup(Object)