+or base64 will be used, depending on what is more efficient.
+
+`qp-or-base64' has another effect. It will fold long lines so that
+MIME parts may not be broken by MTA. So do `quoted-printable' and
+`base64'.
+
+Note: It affects body encoding only when a part is a raw forwarded
+message (which will be made by `gnus-summary-mail-forward' with the
+arg 2 for example) or is neither the text/* type nor the message/*
+type. Even though in those cases, you can use the `encoding' MML tag
+to specify encoding of non-ASCII MIME parts."