I want to validate a text field on a form to match a particular pattern as follows:

PPXnnnn

Where:

First 2 chars = "PP" (upper case)

Next char = upper case letter, eg Q

Next 4 chars = numbers, eg 1111

It would also be good if I could default the PP so the user doesn't have to type it in as it will be the same for each record.

Any help would be appreciated.