Editfield.scrollposition -- how to keep selection visible?

[Erich Rast <Erich dot Rast at t-online dot de>]

Hi,

I need set the selection of a multiline editfield in code, but the 
current selection always has to remain visible. So the editfield has 
to scroll to it when it moves upwards. Does anyone know a decent way 
to compute the vertical scrollposition such that the selection is in 
the middle or the bottom of an editfield?
Is there a way to compute the first line and the last line that is 
fully visible in the editfield?
Thanks and happy computing,

Erich