OW-Time - "hasDuration max 1" restriction on TemporalEntity?

Hello again,

Still looking at the Time Ontology, the Duration section [1] says that "An interval can have multiple duration descriptions, but can only have one duration".

I was expecting to see this "can have only one duration" restriction appear somewhere in the ontology but that does not seem to be the case. Doesn't this translate into a "time:hasDuration max 1" subclass of row in the definition of "time:TemporalEntity" [2]?

Also, a side "rookie" question: the spec uses `only`, `exactly`, `max` and `value` a lot in these "subclass of" sections. I initially thought I would find a definition of these terms somewhere (in OWL, RDFS, Turtle, SHACL, or elsewhere), but that does not seem to be the case. I see how they get translated into an "owl:Restriction" construct in the Turtle file that describes the ontology, which all makes sense to me, but is this pseudo-language defined somewhere?

Thanks,
Francois.

[1] http://w3c.github.io/sdw/time/#duration
[2] http://w3c.github.io/sdw/time/#time:TemporalEntity