code: def get(self, obj_id):
          
          if BasicPage.PAGE_ID_SEPARATOR in obj_id:
              (docid, page_nb) = obj_id.split(BasicPage.PAGE_ID_SEPARATOR)
              page_nb = int(page_nb)
              return self._docs_by_id[docid].pages[page_nb]
          return self._docs_by_id[obj_id]
docs: Get a document or a page using its ID
          Won't instantiate them if they are not yet available