In general it’s somewhat dangerous to assume things about user entered text fields, as it is frequently far more complicated than it seems on the surface (e.g., your example above isn’t close to correct for email addresses: http://en.wikipedia.org/wiki/Email_address#Syntax). Names are another one that is far more complicated in practice: Personal names around the world
However, having said that, something like a callback per character entered to let you apply your own rules seems like it might be good. I’ll forward this thread over to the UMG team.
Cheers,
Michael Noland