We currently have annotations (comments) implementation into JupyterCAD https://github.com/QuantStack/jupytercad/tree/main/src/annotation. This should be moved into another package so that it can be reused in other extensions (Notebook, GlueLab etc). A potential place to put this could be https://github.com/jupyterlab/jupyter_collaboration