-/* Specify whether to results should omit the excluded results rather
- * than just marking them excluded. This is useful for passing a
- * notmuch_messages_t not containing the excluded messages to other
- * functions. */
+/* Specify whether to omit excluded results or simply flag them. By
+ * default, this is set to TRUE.
+ *
+ * If this is TRUE, notmuch_query_search_messages will omit excluded
+ * messages from the results. notmuch_query_search_threads will omit
+ * threads that match only in excluded messages, but will include all
+ * messages in threads that match in at least one non-excluded
+ * message.
+ *
+ * The performance difference when calling
+ * notmuch_query_search_messages should be relatively small (and both
+ * should be very fast). However, in some cases,
+ * notmuch_query_search_threads is very much faster when omitting
+ * excluded messages as it does not need to construct the threads that
+ * only match in excluded messages.
+ */
+