When setting Diagram.isReadOnly to true,How to allow Group expand or collapse?

Here is the example https://jsfiddle.net/dxxzst/vj23yuoz/4/
When I add “isReadOnly: true” to myDiagram, the expand/collapse button is invalid. Is there any solution?

Don’t set Diagram.isReadOnly to true, but instead turn off those permissions that you don’t want the user to be able to do.