Keystroke regular expression (regex) problem

Question

I have a text field that should only permit the following values: "V", "X" or "NA" (all uppercase).
I'm fairly OK with javascript in pdf and I have a script that validates these when the field losses focus.
What would be much better is to have a keystroke script that only permits these values to be entered. I've found elsewhere in the forums a useful starting point here:
var re = /^[A-Za-z0-9 :\\_]$/;
event.change = event.change.toUpperCase();
if (event.change.length >0) {
if (event.willCommit == false) {
    if (!re.test(event.change)) {
        event.rc = false
but I've been unable to come up with anything for the regexp pattern that works reliably (these are definitely not my strong point).
Grateful thanks for any help.

Answer 1

You can apply the RegEX to the keystroke and restrict the keystroke values that be entered or you can use the validation tab to enter a script to restrict the input to specific values.
The script you are using only checks the entered character so it will not test the string "NA" which is 2 characters.
Another approach for such a limited number of input options would be a combo box  or drop down box where the options are space, "V", "X", and "NA". The value of the field would then be limited to a space (no selection made), a V, X, or NA.