little auxiliary window in gtktreeview

[Allin Cottrell <cottrell wfu edu>]

I've just noticed (I'm not sure whether this is new with gtk 2.6) 
that when I hit a letter key over a gtktreeview in my app, a little 
auxiliary window sprouts up (at the bottom right of the treeview), 
containing the letter I typed.  After a few seconds this window 
disappears.

What is the function of this window?  Is it documented somewhere?

--
Allin Cottrell
Department of Economics
Wake Forest University, NC