[Pharo-users] Workspace/Playground/System browser documentation

I am interested into any form of documentation , besides the obvious one (class comments and unit tests) , concerning Workspace, Playgrounds, System Browser, Inspector and Debugger . I am only interested only on documentation about the internals of those tools, I have already studied documentation about their usages and how can be extended from the usual sources. Is there any or am I asking too much ? I will be creating my own System Browser and Workspace in the near future so its important to not replicate code and use what there is already there. But to use code means that I have to understand it first.