I'm assuming you mean that you have a list of error codes and want this list to be included in the running source code for the program (as a hash or array or whatever), and also in the program's documentation, but without duplicating the list of error codes.

There are three real options...

1. Define your messages in your pod, and then make your module parse its own documentation at run-time to extract those messages.

2. Define your messages in your code, and then generate your documentation from that at install time, using something like Pod Weaver.

3. Perl and Pod are two different syntaxes. It is possible (usually using heredocs) to write text which can be executed as Perl and is also seen as Pod. Here's an example:

   use 5.010;
   use strict;
   use warnings;
   
   use Data::Dumper;
   
   our %messages = map /^\s+(.+?):(.+)$/?($1=>$2):(), split "\n", <<'=cut
   +';
   =head1 MESSAGES
   
   The following messages are defined...
   
       eof:Unexpected end of file
       bad_tag:Syntax error in tag
   
   =cut
   
   print Dumper \%messages;
   [download]

   View that file with perldoc and you'll see the list of messages. Execute it, and you'll see they get dumped.