Filtering input entered into a cell

I want to be able to filter input into a cell/column. So for example
I want the cell to only accept hex digits:

grid = new AW.UI.Grid;
// all the usual malarkey...
grid.getColumnTemplate(1).setEvent('onkeypress',acceptOnlyHex);
//...

I get the error that the method is not supported. What is wrong here?

Thanks

Whlist on the subject of restricting input, I'd like to
restrict how many characters can be entered into a cell.
Basically, mimic semantics of maxlength in html.