Why wouldn’t this work over tmux? The authors claims don’t make a whole lot of sense because if this were a cell property, like any other CSI, then it’ll get rendered in the terminal emulator exactly as intended. And we know this because none of the other CSI sequences get garbled over multiplextors.

But for there to be a dedicated section on how multiplexors wouldn’t work suggests to me that the authors already tried this via tmux.

So I’m left wondering what they’ve done with the implementation of this to make that a problem.

I spotted they are using DCS sequences. But even that shouldn’t be an issue itself.

Tmux drops DCS that it doesn't know like this. That aside, this is extra state per cell that needs to be tracked, handled, understood from a rendering perspective etc. It can work, but would require maybe a thousand lines of code or so to support storing and handling state, redraw etc. and all the various edge cases.