On a side note, it's worth mentioning W3C has a working group to standardize in-browser HTML editing (http://dvcs.w3.org/hg/editing/raw-file/tip/editing.html).

The spec is still not settled, but safe to use as a guideline for an implementation. If libraries align their command API implementations with the specs, it would be easy for them to port to use native commands as the browser support gets strong.