var w3cDOM = (document.createElement && document.getElementsByTagName);

function isEmpty(str)
{
    return (str == null || str.length == 0);
}

function isEMailAddr(str)
{
    var re = /^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$/;
    return (str.match(re));
}

function signup()
{
   if (!w3cDOM) return true; // let submit proceed

   var signupForm = document.getElementById('signupForm');

   var eMailAddress = signupForm.email.value;
   if (eMailAddress == 'e-mail-adres')
      eMailAddress = "";

   if (isEmpty(eMailAddress))
   {
      alert('E-mail adres invullen aub.');
      signupForm.email.select();
      return false;
   }
   else if (!isEMailAddr(eMailAddress))
   {
      alert('Geldig e-mail adres invullen aub.');
      signupForm.email.select();
      return false;
   }

   return true;
}