profile

I finally solved the problem I'd been working on the last week or so: what's the Drupal way to limit the length of a profile field?

Problem: don't let users enter more than 4 characters into a field. (E.g., last four of your social, or last four of your passport, etc.)

Google wasn't too helpful. I only learned from Google that I wanted to set the maxlength attribute on the text input field:
<input type='text' maxlength='4'>