code: public function getDocumentNamespace($documentNamespaceAlias)
      {
          if ( ! isset($this->attributes['documentNamespaces'][$documentNamespaceAlias])) {
              throw CouchDBException::unknownDocumentNamespace($documentNamespaceAlias);
          }
  
          return trim($this->attributes['documentNamespaces'][$documentNamespaceAlias], '\\');
      }
docs: Resolves a registered namespace alias to the full namespace.
  
  @param string $documentNamespaceAlias
  @return string
  @throws CouchDBException