anchor.diff:  
   %% ....
   %% ...
  -process(fn, 'unsupported', _Ignore) -> <<"Unsupported">>;
  -process(p, 'unsupported', Bin) ->
  -    {ExtBin, Rest} = sip_binary:parse_token(Bin),
  -    Ext = sip_binary:binary_to_existing_atom(sip_binary:to_lower(ExtBin)),
  -    parse_list('require', Ext, Rest);
  -
  -process(f, 'unsupported', Ext) ->
  -    sip_binary:any_to_binary(Ext);
   
   % Default header processing
   process(p, _Name, Header) -> Header; % cannot parse, leave as is
  
positive.code:     end;
  
  %% 20.39 To
  %% http://tools.ietf.org/html/rfc3261#section-20.38
  process(pn, <<"t">>, _Ignore) -> 'to';
  process(fn, 'to', _Ignore) -> <<"To">>;
  process(p, 'to', Bin) ->
  
negative.code:                                    {'server', <<"HomeServer v2">>}, {'subject', <<"Need more boxes">>},
                                     {'supported', <<"100rel">>}, {'timestamp', <<"54">>},
                                     {'to', <<"sip:bob@localhost">>}, {'unsupported', <<"bar, baz">>},
                                     {'user-agent', <<"Softphone Beta1.5">>},
  
  
                                     {'via', <<"SIP/2.0/UDP localhost">>},
                                     {'x-custom-atom', 25},
                                     {<<"X-Custom">>, <<"value">>}])),
  
       % Already parsed
  