docs: def get_documents(self, doc_format='dict'):
          """ Get the documents returned from Storege in this response.
  
              Keyword args:
                  doc_format -- Specifies the doc_format for the returned documents.
                      Can be 'dict', 'etree' or 'string'. Default is 'dict'.
  
              Returns:
                  A dict where keys are document ids and values depending of the required doc_format:
                      A dict representations of documents (see etree_to_dict());
                      A etree Element representing the document;
                      A raw XML document string.
  
              Raises:
                  ParameterError -- The doc_format value is not allowed.
          """
          def get_doc_id(root, rel_path):
              if not rel_path:
                  return root.text
              else:
                  child = root.find(rel_path[0])
                  if child is None:
                      return None
                  return get_doc_id(child, rel_path[1:])
  
          if doc_format == 'dict':
              return dict([(get_doc_id(document, self._id_xpath), etree_to_dict(document)['document']) for
                          document in self._get_doc_list()])
          elif doc_format == 'etree':
              return dict([(get_doc_id(document, self._id_xpath), document) for
                          document in self._get_doc_list()])
          elif doc_format == 'list-etree':
              return self._get_doc_list()
          elif doc_format == 'list-string':
              return list([(ET.tostring(document)) for
                          document in self._get_doc_list()])
          elif doc_format in ('', None, 'string'):
              return dict([(get_doc_id(document, self._id_xpath), ET.tostring(document)) for
                          document in self._get_doc_list()])
          else:
              raise ParameterError("doc_format=" + doc_format)