whether metadata, in particular attributes or claims supported by a service, can be discovered, if the site's service supports one of the cross-organizational identity protocol families:
Mark includes how, in Liberty Alliance ID-WSF, the identity provider metadata is communicated using a WS-Addressing EndpointReference (EPR). But, in the table where he summarizes mechanisms by which Service Provider metadata is shared, he omits the ID-WSF column.
There are however ID-WSF scenarios, and supporting mechanisms, in which SP metadata is shared. For instance, when subscribing for notifications regarding some attribute of a particular user, an SP can specify the endpoint (once again as a EPR) to which it desires those notifications be sent.