code: def append_warning(self, msg):
          
          assert self.model is not None, "You must already have run make_model!"
          addendum = ('\t<span style="color:red;">(CAUTION: %s occurred when '
                      'creating this page.)</span>' % msg)
          self.model = self.model.replace(self.title, self.title + addendum)
          return self.model
docs: Append a warning message to the model to expose issues.