public function serializeCollection(array $collection, $collectionFormat, $allowCollectionFormatMulti=false)
    {
        if ($allowCollectionFormatMulti && ('multi' === $collectionFormat)) {
            // http_build_query() almost does the job for us. We just
            // need to fix the result of multidimensional arrays.
            return preg_replace('/%5B[0-9]+%5D=/', '=', http_build_query($collection, '', '&'));
        }
        switch ($collectionFormat) {
            case 'pipes':
                return implode('|', $collection);

            case 'tsv':
                return implode("\t", $collection);

            case 'ssv':
                return implode(' ', $collection);

            case 'csv':
                // Deliberate fall through. CSV is default format.
            default:
                return implode(',', $collection);
        }
    }