Create a JSON representation of this event suitable for sending
        to clients.

        .. code-block:: python

            {
                'kind'  : 'RootAdded'
                'title' : <reference to a Model>
            }

        Args:
            references (dict[str, Model]) :
                If the event requires references to certain models in order to
                function, they may be collected here.

                **This is an "out" parameter**. The values it contains will be
                modified in-place.

            buffers (set) :
                If the event needs to supply any additional Bokeh protocol
                buffers, they may be added to this set.

                **This is an "out" parameter**. The values it contains will be
                modified in-place.

def generate(self, references, buffers):
        ''' Create a JSON representation of this event suitable for sending
        to clients.

        .. code-block:: python

            {
                'kind'  : 'RootAdded'
                'title' : <reference to a Model>
            }

        Args:
            references (dict[str, Model]) :
                If the event requires references to certain models in order to
                function, they may be collected here.

                **This is an "out" parameter**. The values it contains will be
                modified in-place.

            buffers (set) :
                If the event needs to supply any additional Bokeh protocol
                buffers, they may be added to this set.

                **This is an "out" parameter**. The values it contains will be
                modified in-place.

        '''
        references.update(self.model.references())
        return { 'kind'  : 'RootAdded',
                 'model' : self.model.ref }