Chris works at socialtext and has been experimenting with Atom and Socialtext for a few, uh, years. See SocialtextAppServer.
Was directed here to determine whether purple numbers are an issue that needs to be brought into the discussion. See them in use on the blog linked above. They provide granular addressability at the level of paragraph, header or list in a body of text, thus they take you inside an entry instead of to an entry.
I've recently implemented a full content RSS 2.0 feed on my blog that includes the purple numbers. It's an interesting mind stretch to play with them. The feed is here: