gistfile1.php

/**
 * Zips must be 5-digit integers and email addresses must be valid.
 */
function email_zip_validate($form, &$form_state) {
  if (!is_numeric((int)$form_state['values']['zip']) || strlen($form_state['values']['zip']) != 5) {
    form_set_error('zip', t('The zip code you entered was not valid. Please try entering it again.'));
  }
  if (!valid_email_address($form_state['values']['email'])) {
    form_set_error('email', t('The email address you entered was not valid. Please try entering it again.'));
  }
}