function checkForm() {
     document.getElementById('mail_cl').color='';
     document.getElementById("warning").innerHTML='';
     var err = false;
     var errMail = false;
     if (!document.getElementById('mail').value.match(/[^\s]/g)) {
       document.getElementById('mail_cl').color='red';
       document.getElementById("warning").innerHTML = document.getElementById("warning").innerHTML+"<br>Please enter your e-mail address.";
       err = true;
       errMail = true;
     }
     var re = /[0-9a-z_]+@[0-9a-z_^\.]+\.[a-z]{2,3}/i;
     if ((!errMail)&&(!document.getElementById('mail').value.match(re))) {
       document.getElementById('mail_cl').color='red';
       document.getElementById("warning").innerHTML = document.getElementById("warning").innerHTML+"<br>Please make sure that your e-mail address is correct.";
       err = true;
     }
     if (err) return false
     else return true;
   }