[whatwg] multiple itemtypes in microdata?

[John Giannandrea]

In the user feedback from the schema.org proposal, which uses microdata as
its syntax, we have seen several use cases that would seem to require
multiple itemtypes per itemscope.

Currently the microdata spec only allows one itemtype which defines the
meaning of the vocabulary for subsequent itemprops.

Allowing an arbitrary list of itemtypes would not be desirable because then
a user agent would have to have knowledge of the type vocabularies in order
to parse the page.

We suggest that itemtype be changed to allow multiple space separated types
(just like itemprop), but only if the origin domain of the types is the
same.  This would allow a vocabulary provider to allow multiple types and to
take responsibility for what the property vocabulary definition is in the
context of more than one type.

-jg