code: def inject(self, contents=None, **kwargs):
          
          if contents and not isinstance(contents, dict):
              raise WrongContentError(self, contents, "contents should be a dict")
          self._stable = False
          if not contents:
              contents = {}
          if kwargs:
              contents.update(kwargs)
          self.content_data.update(contents)
          return self
docs: Adds content data in this element. This will be used in the rendering of this element's childs.
          Multiple injections on the same key will override the content (dict.update behavior).