Hi, I don't know if you need a code for validation, but I have a script object that would do the job for validating 'x' number of pages in a PDF form.
With this script, you could change some of it or base yourself on how it works to make what you want to do to be able to change something on every fields.
The validation script object returns the somExpression of the first field in the hierarchy which fails validation (returns null, 0 or false).
Take a look at the script, this will lead you on the right way for your form and what you are trying to do.
Validation / Reset Functions, easy to manipulate and to change Forms!!!!
Hope this helps!