Widgets can grab the pointer
and keyboard away from other widgets. This essentially
means that the widget becomes "modal"; input goes only
to that widget, and the focus can't be changed to
another widget. A typical reason to grab input is to
create a modal dialog; if a window has the grab,
interaction with other windows is blocked. Note that
there is another, GDK-level "grab"; a GDK keyboard or
pointer grab occurs on an X-server-wide basis---that
is, other applications are unable to receive keyboard
or mouse events. A widget grab is a GTK+ concept; it
only grabs events away from other widgets in the same
application.
