http://schema.org/docs/gs.html#microdata_itemscope_itemtype

For example, author is only available from The New Yorker via this type.

http://www.newyorker.com/tech/elements/hideo-kojimas-mission-unlocked

Note: this is for recognizing (and utilizing) of external sites that use schema.org microdata - not to be confused with the proposed internal support for it, in T106650: Enrich articles with schema.org metadata