Missing subClassOf?

I've been looking at [1] and [2] and the subClassOf property definition [3]
is missing .

[1] http://www.schema.org/docs/full_md.html
[2] http://www.schema.org/Class
[3] http://www.schema.org/subclassOf

-- 
--Alex Milowski
"The excellence of grammar as a guide is proportional to the paucity of the
inflexions, i.e. to the degree of analysis effected by the language
considered."

Bertrand Russell in a footnote of Principles of Mathematics