Required CSS properties to be a conforming Reading Device?

In Section 1.3.5: Relationship to CSS, it states, "A conforming Reading System must render all OPS CSS 2.0 required subset properties," with "required subset properties" linking only to Section 3.0: OPS Style Sheets as a whole. If I scroll down further to Section 3.3: Properties, it just lists the properties supported in the spec, and adds what isn't listed, isn't supported. Now I could infer from that list that all of the properties mentioned are required to be a conforming reading system, but I could also just as easily not. Basically, what I'm getting at is that it's not explicitly stated, or only in a very roundabout way. At the very least, it's not clear.

I propose taking the aforementioned paragraph from Section 1.3.5 (also changing the link there to point directly to 3.3) and also including it directly in Section 3.3 with a little bit of rephrasing to explicitly say these are the properties required to be deemed a conforming reading device. Unless of course I'm misunderstanding and there's an even smaller subset of the properties listed which are the only ones that are required (in which case I'd further list those separately as well).

I'd like to be able to submit bug reports to my reading device supplier, pointing to the spec specifically mentioning their lack of full OPS style conformance, and I know if it's not explicitly clear what's required of them, they'd weasel their way around it.