code: def _registerExtension(self, extension, rtiRegItem):
          
          check_is_a_string(extension)
          check_class(rtiRegItem, RtiRegItem)
  
          logger.debug("  Registering extension {!r} for {}".format(extension, rtiRegItem))
  
          # TODO: type checking
          if extension in self._extensionMap:
              logger.info("Overriding extension {!r}: old={}, new={}"
                          .format(extension, self._extensionMap[extension], rtiRegItem))
          self._extensionMap[extension] = rtiRegItem
docs: Links an file name extension to a repository tree item.