There is a wiki about how to contribute a tool panel with an extension. http://wiki.services.openoffice.org/wiki/Framework/Article/Tool_Panels But there is no detail document about how it is implemented which may help developers understand the mechanism more clearly. I did some study and update below page. http://wiki.services.openoffice.org/wiki/Framework/Article/Tool_Panels_Internals
I am not sure I have fully understood the mechanism. So if there is any mistake in it or any comments on it, feel free to correct me or let me know. Thanks. Lin Yuan
