Tkinter inheritance mess?

[ejetzer]

For a school project, I'm trying to make a minimalist web browser, and
I chose to use Tk as the rendering toolkit. I made my parser classes
into Tkinter canvases, so that I would only have to call pack and
mainloop functions in order to display the rendering. Right now, two
bugs are affecting the program :
1) When running the full app¹, which fetches a document and then
attempts to display it, I get a TclError :
                 _tkinter.TclError: bad window path name "{Extensible
Markup Language (XML) 1.0 (Fifth Edition)}"
2) When running only the parsing and rendering test², I get a big
window to open, with nothing displayed. I am not quite familiar with
Tk, so I have no idea of why it acts that way.

1: webbrowser.py
2: xmlparser.py