function validateForm(form) {
  var emailFilter=/^.+@.+\..{2,4}$/;
  if (!(emailFilter.test(form.user_email.value))) {
    alert ("Please enter a valid email address.");
    form.user_email.focus();
    return false;
  }
  if (form.user_email.value != form.user_email_again.value) {
    alert ("Your email addresses do not match.");
    form.user_email.focus();
    return false;
  }
  if (!form.user_username.value) {
    alert ("Please enter a username.");
    form.user_username.focus();
    return false;
  }
  if (!form.user_password_initial.value) {
    alert ("Please enter a password.");
    form.user_password_initial.focus();
    return false;
  }
  if (form.user_password_initial.value != form.user_password_again.value) {
    alert ("Your passwords do not match.");
    form.user_password_initial.focus();
    return false;
  }
  if (form.user_password_initial.value == form.user_username.value) {
    alert ("Password must be different from username.");
    form.user_password_initial.focus();
    return false;
  }
  var alphaNumFilter=/^\w*$/;
  if (!(alphaNumFilter.test(form.user_password_initial.value))) {
    alert ("Your password can only contain alphanumeric characters.");
    form.user_password_initial.focus();
    return false;
  }
}