contains
Tests if the point at (@x, @y) is contained in @widget.
The coordinates for (@x, @y) must be in widget coordinates, so (0, 0) is assumed to be the top left of @widget's content area.
Return
true if @widget contains (@x, @y).
Parameters
x
X coordinate to test, relative to @widget's origin
y
Y coordinate to test, relative to @widget's origin