Last week we showed you a demo of a problem. We wanted to run two different versions of a program, both operating on different data types... but with the same underlying document.
This is a tricky problem! The old code doesn't natively understand data written by the new system. The new system relies on data the old one doesn't provide. Worst, even in our little toy example there is one field where the data type changes completely, going from a Boolean type to a string.
So, if last week was a prototype of a problem then this week is a prototype of a solution.