The new schema.org by Google, Yahoo and MS recommends usage of the attribute to display the status of products in an online shop:
&
The WHATWG HTML specification mentions, that the LINK-element can either have a rel-attribute:
or an itemprop-attribute
but not both.
The rel-version is restricted to the HEAD-element, whereas the itemprop-version may appear in both, the HEAD and BODY-elements.
http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#the-link-element
What is this WHATWG specification:
whatwg.org/specs/web-apps/current-work/multipage/introduction.html#is-this-html5?