Event for GtkWindow "focus"?

[Robert Roebling t-online de (Robert Roebling)]

  Hi,

under both GTK 1.2 and GTK 2.0, I would like to
know (get notified about) which GtkWindow is
currently "active" or "focussed" or whatever
you call it, basically what the WM tells you
by changing the title bar of a Window. (If
a dialog comes up, the title bar of the original
window will e.g. turn grey and the title bar
of the new dialog will be e.g. blue or better
visible.) Does the WM inform the app in some
way about which window gets the focus or gets
activated?

Thanks for any hint,

  Robert

-- 
Robert Roebling, MD <robert roebling medizin uni-ulm de>