[short]

Interesting! I actually wrote https://github.com/SjonHortensius/LRTEditor to replace CM, but the many subtle browser bugs eventually forced me to abandon it. Do you expect to use shims and possibly let browser-vendors fix bugs/inconsistencies you find?

[marijn]

We're not really using shims, just targeting the lowest-common-denominator contentEditable behavior that we can count on, and implementing anything else ourselves.