Disable A Particular Key in AS3

I know it should be simple, but I can't find a solution to this question.

How do i disable a particular key in AS3?

e.g. disable 'A' key, or 'Minus' key etc...

Thanks in advance for your help.

for a DisplayObject: listen to KeyboardEvent.KEY_DOWN and if event.charCode is one you need to restrict call event.stopImmediatePropagation()
for an input TextField: use TextField.restrict property