function validateForm(alert_message) {
  var emailExpr = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
  if (!document.getElementById('your_email').value.match(emailExpr)) {
    alert(alert_message);
    return false;
  }

  if (document.getElementById('message').value == '') {
    alert(alert_message);
    return false;
  }

  return true;
}

function set_guide() {
  document.getElementById('guide').value = document.getElementById('guides').options[document.getElementById('guides').selectedIndex].value;
}