public function setPriority($priority = '')
    {
        if ('' == $priority) {
            $priority = 'normal';
        }

        switch ($priority) {
            case 'low':
                $priority = Net_Growl::PRIORITY_LOW;
                break;
            case 'moderate':
                $priority = Net_Growl::PRIORITY_MODERATE;
                break;
            case 'normal':
                $priority = Net_Growl::PRIORITY_NORMAL;
                break;
            case 'high':
                $priority = Net_Growl::PRIORITY_HIGH;
                break;
            case 'emergency':
                $priority = Net_Growl::PRIORITY_EMERGENCY;
                break;
            default:
                throw new BuildException(
                    '"priority" attribute is invalid.'
                );
        }

        $this->priority = $priority;
    }