I just tried Squeezer. It's pretty neat and it solves a different
problem. Clearing the contents of the shell window should be a simple
operation.

The undo operation doesn't restore iomark properly, nor does it restore
tags. I've uploaded a newer version of the extension to handle undo.

Binding to the "<<undo>>" virtual event with add="+" didn't work as
expected, so the new undo event handler explicitly calls the older one.
I admit that this code is not ideal.

Should I move this extension to the Cheese Shop and close out this issue?