-Format of results. This option exists as a convenient way to specify
-the format for the default stdout destination. Using a C<format:>
-prefix with the C<--output> destination is preferred otherwise.
+C<maildir> is the default for an existing directory or non-existing path.
+
+Default: C<-> (stdout)
+
+=item --format=FORMAT
+
+=item -f FORMAT
+
+Format of results to stdout. This option exists as a convenient
+way to specify the format for the default stdout destination.
+C<text>, C<json>, C<jsonl>, or C<concatjson> are all supported,
+as are the various mbox variants described in L</--output>.
+
+When a format isn't specified, it's chosen based on the
+L</--output> destination or prefix. C<json> is used for the
+default destination (stdout).
+
+Using a C<format:> prefix with the C<--output> destination is
+preferred when not writing to stdout.