>Is it possible to evaluate, if a textfield/optiongoup... has lost the focus by mouse or by keyboard ?

You can do:

if mdown()
	*Lost focus by Mouse
else
	*Lost focus by Keyboard
endif

in the Lost focus, but this will alwyas return Keyboard if you click outside of the form, otherwise its accurate. To be sure, I would suggest doing this in the GotFocus() if possible, then it would always be right on.