I would like to be able to have requirements for the inputs to a particular text box. For instance, if I have a text box asking for the first name, then the only inputs it should accept are alphabetic characters; no spaces, no commas, no numbers. Similarly, a phone number should expect 9 numerals and three dashes, placed in a specific order. Emails require an @ and a '.' at some point in the message, and have restrictions on other characters.
I would love to be able to specify things like this, as it would prevent responders to our form from making silly mistakes that take time to correct.