How can I view DHXPlanner.class

Hi I’m a newbie in DHTMLX.

I just download and get the dhtmlxScheduler run yesterday.
And as I am trying to change some code, I can’t view the DHXPlanner.class and other config class.
I already tried to search for the answer, but there seem to be no forum mentioned this issue.

Can anyone please guide me of how can I view the DHXPlanner.class?

Thank you very much!