>Hilmar,
>There was a lot of questions in your post. ...

Yes, indeed. And I will still have more questions...

>You can handle the backspace like this:
>

>e.KeyChar == '\b'
>//or
>e.KeyChar == (char)System.Windows.Forms.Keys.Back
>

Thanks, that works. But that immediately reminds me of another question: What is the usual way of checking, for example, for Ctrl or Alt? Say, I want to carry out a special action if the user presses Ctrl-X or something.

>Arrows and tab and delete and probably some other keys are not even captured by the KeyPressed event. I am not 100% sure why. Hopefully someone else knows why

Well, the fact that they are not checked sure simplifies the validation. Perhaps Microsoft wanted to more or less impose, or just simplify programming for, a standard interface. "More or less" because the might be workarounds.

>South America use comma as the decimal separator like in Europe right. That has to do with the culture setting(so on my computer the period is the decimal symbol)

Yes, that is the way my Control Panel is set up.