Changed the title and rearranged several sections.
The communications blocking protocol specified herein is intended to be a user-friendly "front end" to a subset of the functionality defined by the privacy lists protocol (XEP-0016). If a service deploys both privacy lists and the blocking command, the service MUST use the same back-end data store for both protocols. (Note: Wherever possible, this document attempts to define a protocol that is fully consistent with XEP-0016; if a particular aspect of functionality is not specified herein, the relevant text in XEP-0016 shall be taken to apply.)
-A service SHOULD map the blocklist to the default privacy list, where each blocked JID is represented as a privacy list item of type "jid" and action "deny".
When implementing both XEP-0191 and XEP-0016, a service SHOULD map the blocklist to the default privacy list, where each blocked JID is represented as a privacy list item of type "jid" and action "deny".
If all of a user's clients always use the blocking command, then the default privacy list will be equivalent to the blocklist and the default privacy list will be a kind of "virtual list" (in the sense that it is never modified directly by any of the clients).
If one of a user's clients uses privacy lists instead of blocklists and modifies the default privacy list by removing a blocked JID or blocking a new JID, then that change will be reflected in the blocklist.