Index to insert the widget in the list. Notice that the default
of 0 means the widget is inserted at the beginning of the list
and will thus be drawn on top of other sibling widgets. For a
full discussion of the index and widget hierarchy, please see
the Widgets Programming Guide.
New in version 1.0.5.
canvas: str, defaults to None
Canvas to add widget’s canvas to. Can be ‘before’, ‘after’ or
None for the default canvas.