Client side validation outline tests

These will be fleshed out, but as an outline spec what do people think?

Once we have the regex validator working, we can extend this to just to `email` type checking with a pre-defined regex.

_(This is also safe to merge as the tests are all empty and therefore pass)_
Would it be hard / desirable to do something like `"Please provide an age between {{min}} and {{max}}"` ?