Ttk's panedwindow widget.
MHo 2008-04-09: Does someone know if and how it's possible to determine the dimension of a pane inside a panedwindow? I have a canvas inside a pane that holds an image. If resizing / maximizing the top-level windows, everything should grow to use the extra space. But the pane itself says it is has the dimension 1x1, and the canvas stays as its initial size (if I don't specify such initial size, something else goes wrong that is beyond the scope of this question...).