+thread giving a summary of the thread (a relative date, the
+number of matched messages and total messages in the thread,
+participants in the thread, a representative subject line, and
+any tags).
+
+By default, pressing RET on any line displays that thread. The
+'+' and '-' keys can be used to add or remove tags from a
+thread. The 'a' key is a convenience key for archiving a
+thread (removing the \"inbox\" tag). The '*' key can be used to
+add or remove a tag from all threads in the current buffer.