As per the other thread, it sounds like creating individual threads is
the way to go in order to discuss and document changes for Draft 4.

The addition to the <Url> Element section would consist of:

Attributes:

::existing attributes::

rel - Defines the relationship between the OSD file and the Url
described in this element.
Default: "results".
Requirements: This attribute is optional but recommended.  If a rel
value other than "results" is specified for a given format, it should
appear after the "results" <Url> element for compatibility with
existing clients.

This attribute removes the need to hack "suggestions" and other things
into the "format" attribute, and would allow search suggestions to be
provided in a variety of formats (ie <Url format="application/rss+xml"
rel="suggestions" template="foobar"/>)

Other possible "rel" values to document would be:

"preview" - a preview of the search results in a low-resolution format
(see the thread on IE8's usage).
"itemlist" - a complete list of all items within the scope of this
search location
"recent" - a list of items recently added to this scope

And I could probably think of more =)