The other day, a bunch of us were looking at this new feature promised for Leopard, the next iteration of the Mac operating system, and thinking about it as a possible interface for document versioning.

I’ve yet to find something that does this well. Wikis and and Google Docs give you chronological version lists. In Microsoft Word, “track changes” integrates editing history within the surface of the text, but it’s ugly and clunky. Wikipedia has a version comparison feature, which is nice, but it’s only really useful for scrutinizing two specific passages.
If a document could be seen to have layers, perhaps in a similar fashion to Apple’s Time Machine, or more like Gamer Theory‘s stacks of cards, it would immediately give the reader or writer a visual sense of how far back the text’s history goes – not so much a 3-D interface as 2.5-D. Sifting through the layers would need to be easy and tactile. You’d want ways to mark, annotate or reference specific versions, to highlight or suppress areas where text has been altered, to pull sections into a comparison view. Perhaps there could be a “fade” option for toggling between versions, slowing down the transition so you could see precisely where the text becomes liquid, the page in effect becoming a semi-transparent membrane between two versions. Or “heat maps” that highlight, through hot and cool hues, the more contested or agonized-over sections of the text (as in the Free Software Foundations commentable drafts of the GNU General Public License).
And of course you’d need to figure out comments. When the text is a moving target, which comments stay anchored to a specific version, and which ones get carried with you further through the process? What do you bring with you and what do you leave behind?