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

        .. code-block:: python

            {
                'kind'          : 'ColumnsStreamed'
                'column_source' : <reference to a CDS>
                'data'          : <new data to steam to column_source>
                'rollover'      : <rollover limit>
            }

        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'          : 'ColumnsStreamed'
                'column_source' : <reference to a CDS>
                'data'          : <new data to steam to column_source>
                'rollover'      : <rollover limit>
            }

        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.

        '''
        return { 'kind'          : 'ColumnsStreamed',
                 'column_source' : self.column_source.ref,
                 'data'          : self.data,
                 'rollover'      : self.rollover }