Description
Create a background area as defined by the
given window.
Only windows with »-background« receive
a <rect/> representing their region.
ttk-stuff won't be processed here.
highlightThickness isn't used here
borderWidth: centered on the outer line,
duplicate it to get the correct internal
dimensions.
Windows are not independent from their
container. If the container is a canvas
window, then the canvas coordinate system
must be used.
Raised and Sunken are rendered the same way.
Groove will be dealt as a simple line, but with
a lighter stroke, opposite to »solid«.