array( '#process' => array('checkbox_validate_add_validation'), ), ); } /** * Process function for checkbox form elements. */ function checkbox_validate_add_validation($element) { if (isset($element['#required']) && $element['#required'] == TRUE) { $element['#element_validate'] = array('checkbox_validate_validation'); $element['#pre_render'][] = 'checkbox_validate_add_required_symbol'; } return $element; } /** * add required symbol here in this pre_render function * so it doresn't display on error messages */ function checkbox_validate_add_required_symbol($form) { $form['#title'] .= ' *'; return $form; } /** * Validate a required checkbox. */ function checkbox_validate_validation($element) { if (empty($element['#value'])) { form_error($element, t('!title field is required.', array('!title' => filter_xss_admin($element['#title'])))); } }