Misc Widget Abstract.
This is an abstract for a set of utility widgets
that lack a physical window. They do have
alignment and padding within their defined space.
Without a window, widgets of this type cannot capture events.
To capture events place in Gtk_EventBox.
Specify how to position the child
widget when it is not allocated all the space available to it.
A value of 0.0 positions the widget to the left or
top of its allocated space. A value of 1.0 positions
the widget to the right or bottom of its allocated space. Specifying
0.5 will center the widget in its allocated space.