docs: def _read_collections(self, graph):
          """
          Read graph and add collections to document
          """
          for e in self._get_elements(graph, SBOL.Collection):
              identity = e[0]
              c = self._get_rdf_identified(graph, identity)
              members = []
              # Need to handle other non-standard TopLevel objects first
              for m in graph.triples((identity, SBOL.member, None)):
                  members.append(self._collection_store[m[2].toPython()])
              obj = Collection(members=members, **c)
              self._collections[identity.toPython()] = obj