Barry raised reasonable objections to the macro name \mimeheader, so
we'll simply revert to \mailheader since there's no other good name.
diff --git a/Doc/lib/libcookie.tex b/Doc/lib/libcookie.tex
index a84ad36..43d5ada 100644
--- a/Doc/lib/libcookie.tex
+++ b/Doc/lib/libcookie.tex
@@ -19,7 +19,7 @@
\begin{excdesc}{CookieError}
Exception failing because of \rfc{2109} invalidity: incorrect
-attributes, incorrect \mimeheader{Set-Cookie} header, etc.
+attributes, incorrect \mailheader{Set-Cookie} header, etc.
\end{excdesc}
\begin{classdesc}{BaseCookie}{\optional{input}}