-can be run on more than one message, but on a large number of messages
-may attempt to open too many files.
+can be run on each message separately, e.g., using a Bourne shell loop:
+.PP
+.RS
+.nf
+for msg in \`pick +folder\`; do mhfixmsg +folder $msg; done
+.fi
+.RE
+.PP
+The two appearances of the
+.B +folder
+switch in that command protect against concurrent context changes by other
+.B nmh
+command invocations.