How are you trying to restrict it? If you're trying to
restrict it uniformly, for example, to entirely numerical inputs,
then the easiest way I know of to do so is with an itemEditor. You
can just add the same itemEditor to each column that way.
This only saves work over custom renderers if you're trying
to restrict multiple columns in the same manner, but for numeric
only tables, it's pretty short.
You could probably also do it with itemEdit and
itemEditBeginning events, but that would likely be more work then
simply declaring a single global itemEditor and using it in all