-Fix the insane quoting nightmare of the test suite, (and once we do
-that we can actually test the implicit-phrase search feature such as
-"notmuch search 'body search (phrase)'"
+Implement a syntax for requesting set-theoertic operations on results
+of multiple searches. For example, I would like to do:
+
+ "tag:inbox" SET-SUBTRACT "tag:muted"
+
+ as well as:
+
+ "tag:notmuch and <date-range>" SET-INTERSECT
+ "tag:notmuch and not (tag:merged or tag:postponed)"
+
+ See id:3wdpr282yz2.fsf@testarossa.amd.com for more details on the
+ use cases of the above.
+
+Database changes
+----------------
+Store a reference term for every message-id that appears in
+References. We just started doing this for newly-added documents, but
+at the next convenient database-schema upgrade, we should go back and
+fix old messages to be consistent.
+
+Start indexing the List-Id header, (and re-index this header for
+existing messages at the next database upgrade).
+
+Add support for the user to specify custom headers to be indexed (and
+re-index these for existing messages at the next database upgrade).
+
+Test suite
+----------
+Achieve 100% test coverage with the test suite.