Require 1 of 3 Fields

Hello,

I have a form that has three text input fields, First Name, Last Name, Email.

I need for the user to enter at least 1 of the 3. It doesn't matter which, as long as 1 is filled.

How can I set up my form to require at least 1 of these 3 fields?

Thanks,
Ryan

Thanks Bob.

I didn't know what it was called, and I was able to look up custom validation in the FAQ and found the solution.

Thanks!
Ryan