String entry format enforcement?

String entry format enforcement?

I have a requirement to enter a string the format of which should be 3 letters, followed by 6 numbers
AAA123456
I can't find the manual section that helps me deal with ensuring data entry occurs in this manner.
The only thing I can think of so far is having two keyboard, one with only letters, another with only numbers and having two data entry boxes, one triggering the number keypad, the other triggering the letter keypad, then stitch the two strings together somehow. Clearly this is awkward extra complexity that nobody really needs.
Is anybody aware of a generic string format functionality that would ensure I get my inputs formatted correctly?

This is a migrated post! Originally posted on 26.08.2016 by user EdgyUsername. Please be aware that information can be outdated.