"But I don't understand it that well either, I just look at examples: find another inspector pane that looks or acts the way you want and go from there."
I think its reasonable to assume that if someone does not find documentation will at least try to find examples. But example dont tell the full story , they dont describe intent, the why and the how, they only describe the what. In any case thanks for the pointers, I have not considered GTInspector and GT tools and I should have because they really back some very useful features and they seem quite customisable.
