code: def set(self, instance, value, **kwargs):
          
          # Retrieve the proxy object
          proxy_object = self.get_proxy(instance)
  
          # Return None if we could not find a proxied object, e.g. through
          # the proxy expression 'context.getSample()' on an AR
          if not proxy_object:
              logger.debug("Expression '{}' did not return a valid Proxy Object on {}"
                           .format(self.proxy, instance))
              return None
  
          # Lookup the proxied field by name
          field_name = self.getName()
          field = proxy_object.getField(field_name)
  
          # Bail out if the proxy object has no identical named field.
          if field is None:
              raise KeyError("Object '{}' with id '{}' has no field named '{}'".format(
                  proxy_object.portal_type, proxy_object.getId(), field_name))
  
          # set the value on the proxy object
          field.set(proxy_object, value, **kwargs)
  
          # get the current time
          now = DateTime.DateTime()
  
          # update the modification date of the proxied object
          proxy_object.setModificationDate(now)
  
          # update the modification date of the holding object
          instance.setModificationDate(now)
docs: writes the value to the same named field on the proxy object