In PWG 5100.20, page 16, it says this:
Printers that report support for TLS MUST also support HTTP Upgrade to TLS,
correctly advertise themselves using the "_ipps._tcp,_print" sub-type, and
support using an "ipps" URI.
This is not a conformance requirement from 5100.14, however. So B-5.1
really ought to be removed or at least be made into a SHOULD rather than a