Date String Validation

[bh2smith]

Nitpick: do you care about validating these dates match the format you want?

We could use regex pattern matching for YYYY-MM-DD

something like this:

^\d{4}\-(0[1-9]|1[012])\-(0[1-9]|[12][0-9]|3[01])$

credit to this person with their nice diagram!

Originally posted by @alfetopito in #260 (comment)