def validate_iso_date key, value, opts
      if opts[:iso_date]
        return value.strftime("%Y-%m-%d")  if value.respond_to?(:strftime)
      end
      value
    end
def validate_iso_date key, value, opts
      if opts[:iso_date]
        return value.strftime("%Y-%m-%d")  if value.respond_to?(:strftime)
      end
      value
    end
Validates specified `value` with `re` field.
 @param [Object] key Value to validate.
 @param [Object] value Value to validate.
 @param [Hash] opts opts with optional re field.
 @return [Object] Updated `value`