converting validation pattern to script syntax and running check

Hi,

I am working on a form where I want to have users enter info in a field called "ID Number" according to a strict pattern. In this case AAA9999-A.

However, if the pattern is not met, I want the field to reset and the focus to be put back into the field. In other words, I don't want the user to move on in the form unless they have entered the value in the field according to the pattern.

It looks like using a validation pattern does not have the capability of clearing the field input and setting the focus. So I wanted to know the best way to do that with script. The only thing is, I don't know how to convert the validation pattern into script syntax and then check for it.

Any ideas?