CI_Form_validation::_build_error_msg PHP Method

    protected function _build_error_msg($line, $field = '', $param = '')
    {
        // Check for %s in the string for legacy support.
        if (strpos($line, '%s') !== FALSE) {
            return sprintf($line, $field, $param);
        }
        return str_replace(array('{field}', '{param}'), array($field, $param), $line);
    }