Comment on "Validation Functions" - What happens when validation changes?

[greggman]

I'm guessing this is answered later in the book but ...

When I was reading the part "Validation Functions" I started wondering what happens if I change the validation. Let's say I start with no requirements, then later require atitle field and there are documents that don't have a title.

I'm not asking for an answer here. Just wondering if a comment in the book that it will be answered later in the book or a callout that describes the process or if there is no process then even something that says "If you change validation and old documents don't pass your S.O.L., read and write every document so it will pass validation and only then install the new validation". Or something?

I'm new to all of this so maybe that's obvious