This looks like Twitter's version of Web Components?

You might have heard of it shadow DOM etc. Basically the idea is to be able to add GUI components eg <progressbar> that are as integrated as the native ones are.

https://dvcs.w3.org/hg/webcomponents/raw-file/tip/explainer/... https://plus.google.com/103330502635338602217/posts

Mozilla's X-Tags implementation seems closer to the goal though: http://www.x-tags.org/ IIRC it can do this because it's using Object.observable internally to detect DOM changes.

ie with X-tags you don't need the javascript definition part, just: <x-map data-key="39d2b66f0d5d49dbb52a5b7ad87aea9b"></x-map>.