The Scintilla component is the only rational choice for an editor, but yes, it lacks a proper documentation. The best source/reference is certainly this page.
The API documentation and the wiki are useful sources too. The wxPython docs and demos also contain exemples using the control.
Finally, note that wxStyledTextCtrl is a (thin) wrapper around the (fat) Scintilla API, so the latter can be used as a reference too.