function definedBy($key, $returnchannel = false)
    {
        foreach ($this->layers as $layer) {
            $channel = $this->getDefaultChannel();
            if ($channel !== 'pear.php.net') {
                if (isset($this->configuration[$layer]['__channels'][$channel][$key])) {
                    if ($returnchannel) {
                        return array('layer' => $layer, 'channel' => $channel);
                    }
                    return $layer;
                }
            }

            if (isset($this->configuration[$layer][$key])) {
                if ($returnchannel) {
                    return array('layer' => $layer, 'channel' => 'pear.php.net');
                }
                return $layer;
            }
        }

        return '';
    }