docs: def matches(property_name, regex, *, present_optional=False, message=None):
      """Returns a Validation that checks a property against a regex."""
      def check(val):
        """Checks that a value matches a scope-enclosed regex."""
        if not val:
          return present_optional
        else:
          return True if regex.search(val) else False
  
      return Validation(check, property_name, message)