The base definition of XML doesn't specify hyperlinks. But XLink does, and because XML has namespaces, it can be integrated into any other namespace-aware XML application without risk of collisions: http://www.w3.org/TR/xlink/
No definition of XML does.
> But XLink does
By having the client understand xlink exists and accessing xlink attributes you get links. This is no different than specifying that there are URL values corresponding to specific keys in your JSON-derived media type.
An XLink-containing document is a media type derived from XML in the exact same manner.
> and because XML has namespaces, it can be integrated into any other namespace-aware XML application without risk of collisions: http://www.w3.org/TR/xlink/
Not really relevant to the discussion, is it?