-In all cases, a relative FCC directory will be understood to
-specify a directory within the notmuch mail store, (as set by
-the database.path option in the notmuch configuration file).
+If `notmuch-maildir-use-notmuch-insert' is set (the default) then
+the header should be of the form \"folder +tag1 -tag2\" where
+folder is the folder (relative to the notmuch mailstore) to store
+the message in, and tag1 and tag2 are tag changes to apply to the
+stored message. This string is split using `split-string-and-unquote',
+so a folder name containing spaces can be specified by
+quoting each space with an immediately preceding backslash
+or surrounding the entire folder name in double quotes.