function cmdSubmit_click() {
  
  var frm = document.getElementById("frm");
  
  var username  = document.getElementById("username");
  var email = document.getElementById("email");

  if (username.value.length<1 && email.value.length<1) {
    alert("Please enter either your username or your email address.");
    username.focus();
    return false;
  }
  
  if (username.value.length>0 && email.value.length>0) {
    alert("Please enter either your username or your email address, but not both.");
    username.focus();
    return false;
  }
  
  frm.submit();
  return true;
  
}