extending a rich text box control

[Cosimo Galasso]

I need to extend the rich text box control, adding a new item in the context
menu.
When clicking on the new item a new window should appear, containg a tree
view.
Picking an iten in the trree view some xhtml node should be added in the
rich text box control.

Some one can help me in finding some documentation for doing it ?
Or can suggest me an alternative way ?

Thanks
Cosimo