protected function editFieldhandlerMethod()
    {
        if (in_array($this->method, array('validate', 'sanitize', 'format'))) {
            return $this;
        }

        throw new InvalidArgumentException(
            get_class($this)
            . ' passed in invalid Fieldhandler method '
            . $this->method
            . ' in FieldhandlerUsageTrait::editFieldhandlerMethod.'
        );
    }