code: def register(self, id):
          
          assert isinstance(id, basestring)
          if id in self.used_:
              #FIXME
              errors.error("common: the configuration '$(id)' is in use")
  
          if id not in self.all_:
              self.all_.add(id)
  
              # Indicate that a new configuration has been added.
              return True
          else:
              return False
docs: Registers a configuration.
  
              Returns True if the configuration has been added and False if
              it already exists. Reports an error if the configuration is 'used'.