Define the \mailheader macro and document conventions for using it.

Doc/doc/doc.tex

@@ -834,6 +834,17 @@ This \UNIX\ is also followed by a space.
       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}

Doc/perl/python.perl

@@ -212,6 +212,8 @@ sub do_cmd_longprogramopt{
     return use_wrappers(@_[0], '<b class="programopt">---', '</b>'); }
 sub do_cmd_email{
     return use_wrappers(@_[0], '<span class="email">', '</span>'); }
+sub do_cmd_mailheader{
+    return use_wrappers(@_[0], '<tt class="mimeheader">', '</tt>'); }
 sub do_cmd_mimetype{
     return use_wrappers(@_[0], '<span class="mimetype">', '</span>'); }
 sub do_cmd_var{

Doc/texinputs/python.sty

@@ -833,6 +833,7 @@
 \newcommand{\ctype}[1]{\texttt{#1}}     % C struct or typedef name
 \newcommand{\cdata}[1]{\texttt{#1}}     % C variable, typically global
 
+\newcommand{\mailheader}[1]{\texttt{#1}}
 \newcommand{\mimetype}[1]{{\small\textsf{#1}}}
 % The \! is a "negative thin space" in math mode.
 \newcommand{\regexp}[1]{%