Support ranges for the DATE type
rtvref.types.DATE type currently does not have arguments. The only way to support date ranges would be via a custom validator. We could add support for arguments with a variety of properties to check that a value is in an inclusive and/or exclusive date range.
Date range argument values should be ISO 8601 UTC strings so that they are JSON-serializable. We could say that a date value would first be converted from local to UTC, and then compared against the range.