>I'm trying to build a txtbox that only accept numbers and ?,* symbols and esc,backspace,home,end,enter etc (no letters).
>How can i delete de key value from the buffer so if it's not one of the above, doesn't include in the txtbox.value.


If they character isn't one that you want, use NODEFAULT. It will keep the textbox from processing the keystroke. For example:

IF Alpha
NODEFAULT
ENDIF