Is complex field validation possible with WebForm? WebForm is a very nicely done module, but (at least at first glance) it seems to lack some things that I expect to need.

Specifically, I'd like a way to specify more complex field requirements than just a boolean.  For instance, what if I have a form with an e-mail address field and a telephone field, and I want the user to be required to enter at least one of the two.  In other words, if they enter an e-mail address, they don't need to enter a phone number; and if they enter a phone number, they don't need to enter an e-mail address.

Is this possible with WebForm?
Try using the WebForm Validation module.


  The following validation rules are currently included:
  
  
  Numeric values (optionally specify min and / or max value)
  Minimum length
  Maximum length
  Minimum number of words
  Maximum number of words
  Equal values on multiple fields
  Unique values on multiple fields
  Specific value
  Require at least one of two fields
  Require at least one of several fields
  Minimum number of selections required
  Maximum number of selections allowed
  Exact number of selections required
  Plain text (disallow tags)
  Regular expression
  Must be empty (Anti-Spam: Hide with CSS)  
  Words blacklist  
  Must match a username