Pre-defined user list

Hi Guys I'm trying to create a question in a form where one is asked for an ID however I want the ID entred checked in the background against a predefined list and if it exist the data collector can move to next question and if the ID in not in the list they get a prompt for required_message to enter correct ID. I need toknow what constraint in my X-Form to make this work.

If the ID should match a particular format, then you can use a regular expression. has more.

If you really want to match an ID from a list, you can try using pulldata() to match against an ID in a CSV. has more.