the jsomers.net blog.

If you’ve ever typed anything into a Google Doc, you can now play it back as if it were a movie — like traveling through time to look over your own shoulder as you write.

This is possible because every document written in Google Docs since about May 2010 has a revision history that tracks every change, by every user, with timestamps accurate to the microsecond; these histories are available to anyone with “Edit” permissions; and I have written a piece of software that can find, decode, and rebuild the history for any given document.

The details are here.