public function addTarget($target, array $config)
    {
        $ext = $this->getExt($target);
        $config += [
            'files' => [],
            'filters' => [],
            'theme' => false,
            'extend' => false,
            'require' => [],
        ];
        if (!empty($config['paths'])) {
            $config['paths'] = array_map(array($this, '_replacePathConstants'), (array)$config['paths']);
        }
        $this->_targets[$target] = $config;
    }