+If ``x'' is ommitted, it will default to the ``Subject'' header field.
+The form ``/to:y'' is a special case, and will expand
+to all messages containing the substring ``y'' in the ``To'', ``Cc''
+or ``Bcc'' header fields.
+The check for "to" is case sensitive, so that
+``/To:y'' can be used to limit the search for ``y'' to just
+the ``To:'' field.