v2 validation: atomize checks

#288 introduces a new validation frame work. so far, a lot of v1 code is reused, and many things are checked together. however, it would be preferable to have more fine-grained checks.

Start by reading issue #288 and the validation framework it introduced, then compare the reused v1 validation code described here. Define the individual checks and their boundaries before changing the validation structure; done means the previously combined checks can be run and reported independently.