 depend on regular bounds computation that depends on all Nodes existing
      this.diagram.fixedBounds = computeDocumentBounds();

      this.diagram.remove(VirtualizedTreeEdge._dummyFromNode);
      this.diagram.remove(VirtualizedTreeEdge._dummyToNode);
      this.diagram.remove(VirtualizedTreeEdge._dummyLink);

      // update the positions of any existing Nodes
      this.diagram.nodes.each((node) => node.updateTargetBindings());
    }

    setPortSpots(v) {
      v.destinationEdges.each((e) => {
      