Define the \mailheader macro and document conventions for using it.
diff --git a/Doc/doc/doc.tex b/Doc/doc/doc.tex
index 9cf1d77..afb59f7 100644
--- a/Doc/doc/doc.tex
+++ b/Doc/doc/doc.tex
@@ -834,6 +834,17 @@
used.
\end{macrodesc}
+ \begin{macrodesc}{mailheader}{\p{name}}
+ The name of an \rfc{822}-style mail header. This markup does
+ not imply that the header is being used in an email message, but
+ can be used to refer to any header of the same ``style.'' This
+ is also used for headers defined by the various MIME
+ specifications. The header name should be entered in the same
+ way it would normally be found in practice, with the
+ camel-casing conventions being preferred where there is more
+ than one common usage. For example: \mailheader{Content-Type}.
+ \end{macrodesc}
+
\begin{macrodesc}{mimetype}{\p{name}}
The name of a MIME type.
\end{macrodesc}