Meaningful use of "validate" and friends in Tkinter

[Fredrik Juhlin]

Hello,
 
I stumbled over the configurations "validate", "validatecommand" and friends
in the Entry widget today. I tried to make something useful with it (eg,
give the validation function the string to validate as an argument) but I
found myself stumped.
 
Has anyone been able to put them to good use, and if so, how? :)
 
Thanks in advance,
FJ