* authors of mail messages in the query results that belong to this
* thread.
*
+ * The string contains authors of messages matching the query first, then
+ * non-matched authors (with the two groups separated by '|'). Within
+ * each group, authors are ordered by date.
+ *
* The returned string belongs to 'thread' and as such, should not be
* modified by the caller and will only be valid for as long as the
* thread is valid, (which is until notmuch_thread_destroy or until