Thanks for the update David! Mohsen and I had a nice meeting here in SF. Talked through how the web components adapter might make use of Forms JS lib. Things look good now, though it became apparent that I need to focus on the use-case of better supporting collections and we all (eventually) need to think more about the view/layout schema. Expect PRs from Mohsen and myself this week regarding those as well. :)
Anyways I'd think custom function validators should be used for anything that starts being complicated, arrays feels like one of those things :) By using custom validators we keep the core schema nice and clean.
I agree with David re: custom validators. Fwiw I think the fears about things being too complicated are maybe unfounded. Forms JS already impliments all of the validation rules we've discussed- and they're all unit tested too
I'm just opening a question or two for discussion as we take the last thing- which is collection validation.