Provide a nice way to share data with markdown ("%% md") too without direct manipulation of the DOM

As discussed in gitter, It would be nice to have a nice way to share data with markdown ("%% md") too without direct manipulation of the DOM.

Even better with some directives to bind data to the DOM, and manipulate it too. If I'm thinking, something like angular/vuejs; if, for, show, hide .. etc.

No files, tests, or entry points are named. Start by locating the implementation for %% md cells and the current data/DOM-sharing behavior, then clarify the directive and binding scope with maintainers. Completion would require an agreed, tested way to share data with markdown without direct DOM manipulation.

Written by the indexing model from the issue text.