[poe] Issue: Informative references to schema, vcard, & foaf marked as Vocab

iherman has just labeled an issue for https://github.com/w3c/poe as "Vocab":

== Informative references to schema, vcard, & foaf ==
A number of vocabulary items in section 3 of the vocab documents (eg, Party) declares itself to be a subclass of various foaf, schema, and vcard classes. Section 3 is normative, but these classes are referred to as informative. It is better to add, at the beginning of the section, a statement of the sort:

> Any reference to vocabulary items other than ODRL terms are considered to be informative.

I do not believe that has any effect on any implementations.

(This issue came up during the PR transition discussion with the Director.)

See https://github.com/w3c/poe/issues/285