address test with multiple addresses?

How is the address test suppose to handle multiple addresses?

For instance, if my message has:

To: leg(_at_)andrew(_dot_)cmu(_dot_)edu, sg3y(_at_)andrew(_dot_)cmu(_dot_)edu

and I test

if address :localpart :is "to" "sg3y" {
  fileinto "INBOX.silly";
}

does this match?  When should it match with multiple addresses?

Thanks,
Larry