public function setChannelElement($elementName, $content, array $attributes = null, $multiple = false)
    {
        if (empty($elementName))
            throw new \InvalidArgumentException('The element name may not be empty or NULL.');
        if (!is_string($elementName))
            throw new \InvalidArgumentException('The element name must be a string.');

        $entity['content'] = $content;
        $entity['attributes'] = $attributes;

        if ($multiple === TRUE)
            $this->channels[$elementName][] = $entity;
        else
            $this->channels[$elementName] = $entity;

        return $this;
    }