True read-only cells

[jhamrick]

nbgrader currently has pseudo "read-only" cells where they are "read-only" in the sense that their contents get saved to the nbgrader database, and then overwritten during grading if they have been changed by the student. I have reports that this is confusing, and requests for true read-only cells where the cell actually cannot be edited at all in the live notebook.

I think this would be really useful to have for nbgrader. We could keep it as an undocumented feature for the moment, just like "undeletable" cells are, until we can figure out an appropriate UI for it.

[Carreau]

Do you want it in the core? Or as an extension ?

By read-only, I suppose you want users to not be able to clear output, and not modify the text of cell.
Can they enter edit mode for markdown cell, or just see the rendered version ?
Should they be allowed to select the text ? (Codemirror as 2 read-only option: readOnly:true|'nocursor')
Copy the cell ?
Past it ?
If pasted, is the new cell read-only too ? Or not ?

[jhamrick]

Yes, I'd like it in core. Ideally students shouldn't have to install anything extra.

By read-only, I suppose you want users to not be able to clear output, and not modify the text of cell.

I would be ok with clearing output -- just not editing the source of the cell. I think not being able to clear the output (or overwrite it, if the cell is re-run) could be confusing.

Can they enter edit mode for markdown cell, or just see the rendered version ?

I think they should probably be able to see the source of markdown, just not edit it.

Should they be allowed to select the text ? (Codemirror as 2 read-only option: readOnly:true|'nocursor')

I think disabling the cursor would be fine.

Copy the cell ?
Past it ?
If pasted, is the new cell read-only too ? Or not ?

Yes, it should be copiable, and pasted versions shouldn't be read-only. I would expect the behavior to be similar to how the "undeletable" property is maintained (and actually, "read-only" should imply "undeleteable", I think).

[yuvipanda]

Is there even a way to enforce this 'serverside' at all? If not, just adding a 'readonly' field to cell metadata and enforcing it in client side JS (either in an extension or core) would be enough, right?

[yuvipanda]

(pressed wrong button, sorry!)

[jhamrick]

No, it's something that the frontend would have to support. So yeah, adding a 'readonly' field to the cell metadata and then enforcing it in the core notebook client JS (this is also how the 'deletable' field works).

[takluyver]

Yes, if/when we document this, we should make it clear that it's a 'stop users shooting themselves in the foot' measure, not a security measure.