Visualize diff between revisions

It's nice to see revisions are kept for future review. It could be even better if there's an user interface to check the diff between revisions visually. Here's an example from Google Docs:

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An easy approach is to render the two revisions and feed them to a HTML diff tool (e.g. [htmldiff.js]( which works pretty well in highlight diffs by <ins> and <del> elements.

A clearer way could be running a diff on the doc source file and render the diff. This may result in many corner cases and need to handled with great care.