Hi Jun,
Which part is not clear? - It's been a very long 'winter' since I last had to put my hands on WDJ, but last I checked all versions below 7.31 did not had a closure / anonymous function on the main loading script. So that makes easier on most versions prior 7.31...
Even had said such, you still can access the private members and redefine or enhance them.. it's just a little bit more work.
Hope it helps,
D.