The cell data is always stored as plain text, on the client side simply with an attribute. And you can only ever edit cells as text, so those issues never come up. I could see how the checkbox would be tough though because you'd have to decide which line they clicked on in the text representation.

I've thought about porting to Jupyter too, but the plugin system on JupyterLab is pretty involved, and you lose plain text storage on the server side.