How to open a pop-up form for the elements from the diagram?

[atejshee-tibco]

I am experimenting using the project template (node-json-vscode) from https://github.com/eclipse-glsp/glsp-examples/tree/master/project-templates/node-json-vscode, wherein I have added couple of new elements in the existing Custom JSON model and rendered those on UI. Now I want to add the feature such that, if a user clicks on an edge or a node, then it should open a small pop-up form (or some similar structure), and in that pop-up form, the user can enter values for couple of more attributes for that edge or node.

Is there any simple example that could assist me to acheive this? Or what needs to be done to acheive such a feature?