Possible values are `oldest-first', `newest-first'
or nil. Nil means use the default sort order.
:search-type Specify whether to run the search in search-mode,
- tree mode or unthreaded mode. Set to 'tree to specify tree
- mode, 'unthreaded to specify unthreaded mode, and set to nil
- (or anything except tree and unthreaded) to specify search mode.
+ tree mode or unthreaded mode. Set to `tree' to
+ specify tree mode, 'unthreaded to specify
+ unthreaded mode, and set to nil (or anything
+ except tree and unthreaded) to specify search
+ mode.
Other accepted forms are a cons cell of the form (NAME . QUERY)
or a list of the form (NAME QUERY COUNT-QUERY)."