@dave Updated the post to link to the IndieWeb wiki page about it. It's a format I proposed a few years ago, basically just a ZIP file of posts (HTML, JSON, and images). The goal is to make it easier to package up posts and move them between systems or back them up.
@manton -- maybe we should have a conversation about that, because anything with that kind of name should be some kind of a consensus, imho.
@manton -- i came up with something like this in 2002 called RSS 2.0, and this is specifically provided for in the source namespace. i think it's important if you want lots of support in something like this to not "welcome input" rather "steal from the best." ;-)