public function setLabelPosition($labelPosition)
    {
        $labelPosition = strtolower($labelPosition);
        if (!in_array($labelPosition, array(self::LABEL_APPEND, self::LABEL_PREPEND))) {
            throw new Exception\InvalidArgumentException(sprintf(
                '%s expects either %s::LABEL_APPEND or %s::LABEL_PREPEND; received "%s"',
                __METHOD__,
                __CLASS__,
                __CLASS__,
                (string) $labelPosition
            ));
        }
        $this->labelPosition = $labelPosition;

        return $this;
    }