Suggested copy edits to 2 way binding article.

I think this isn't quite right. The virtual DOM is working fine. What this illustrates is actually an issue with React's philosophy of only storing the minimum of state and re-calculating as much as possible on the fly rather than storing lots of state and using bindings to sync it. If you show, and let users edit, calculated values rather than stored ones, you need to have functions a->b and b->a that work precisely, so that a->b->a is always exactly a.