line. This is the only guaranteed portable way to avoid having such
lines be mistaken for a \UNIX{} mailbox format envelope header separator (see
\ulink{WHY THE CONTENT-LENGTH FORMAT IS BAD}
-{http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html}
+{http://www.jwz.org/doc/content-length.html}
for details). \var{mangle_from_} defaults to \code{True}, but you
might want to set this to \code{False} if you are not writing \UNIX{}
mailbox format files.