code: def definition(self, name):
          
          d = self.definitions.get(name)
          if d is None:
              raise AttributeError(name)
          return d
docs: Get the definition for the property I{name}.
          @param name: The property I{name} to find the definition for.
          @type name: str
          @return: The property definition
          @rtype: L{Definition}
          @raise AttributeError: On not found.