Remove a model as root model from this Document.

        Changes to this model may still trigger ``on_change`` callbacks
        on this document, if the model is still referred to by other
        root models.

        Args:
            model (Model) :
                The model to add as a root of this document.

            setter (ClientSession or ServerSession or None, optional) :
                This is used to prevent "boomerang" updates to Bokeh apps.
                (default: None)

                In the context of a Bokeh server application, incoming updates
                to properties will be annotated with the session that is
                doing the updating. This value is propagated through any
                subsequent change notifications that the update triggers.
                The session can compare the event setter to itself, and
                suppress any updates that originate from itself.

def remove_root(self, model, setter=None):
        ''' Remove a model as root model from this Document.

        Changes to this model may still trigger ``on_change`` callbacks
        on this document, if the model is still referred to by other
        root models.

        Args:
            model (Model) :
                The model to add as a root of this document.

            setter (ClientSession or ServerSession or None, optional) :
                This is used to prevent "boomerang" updates to Bokeh apps.
                (default: None)

                In the context of a Bokeh server application, incoming updates
                to properties will be annotated with the session that is
                doing the updating. This value is propagated through any
                subsequent change notifications that the update triggers.
                The session can compare the event setter to itself, and
                suppress any updates that originate from itself.

        '''
        if model not in self._roots:
            return # TODO (bev) ValueError?
        self._push_all_models_freeze()
        try:
            self._roots.remove(model)
        finally:
            self._pop_all_models_freeze()
        self._trigger_on_change(RootRemovedEvent(self, model, setter))