How to start hacking the src of the panel applets?

["deng.guang" <deng guang 163 com>]

I'm a new developer. I want to do something about the panel applets. But
where can I find good panel applet programming reference or guide. I
don't want to spent time in vain and want to be efficient. Please help
your future good developing friend;).Any hint will be very appreciated.