new syntax for RequiredValidUntil filter

[Tom Scavo]

Just saw this appear in the wiki docs:

<MetadataFilter xsi:type="RequiredValidUntil" maxValidity="P14D"/>

"If a zero duration is specified (which is the default), the filter
performs no action."

There's probably a good reason for the latter but it makes no sense.
Why not REQUIRE @maxValidity instead?

Thanks,

Tom