anchor.diff:                                     {'authorization', <<"Digest username=\"Alice\"">>}, {'call-id', <<"callid">>},
                                      {'call-info', <<"<http://www.example.com/alice/photo.jpg>">>}, {'contact', <<"*">>},
                                      {'content-disposition', <<"session">>}, {'content-encoding', gzip},
  -                                   {'content-language', 'en'},
  +                                   {'content-language', 'en'}, {'content-length', 5},
   
                                      {'content-length', <<"5">>}, {'via', <<"SIP/2.0/UDP localhost">>},
                                      {'from', <<"sip:alice@localhost">>}, {'to', <<"sip:bob@localhost">>},
  
positive.code:     format_address(Addr);
  
  %% 20.11 Content-Disposition
  process(fn, 'content-disposition', _Ignore) -> <<"Content-Disposition">>;
  process(p, 'content-disposition', Bin) ->
      {TypeBin, Rest} = sip_binary:parse_token(Bin),
  
negative.code:     sip_binary:any_to_binary(Allow);
  
  %% 20.13 Content-Language
  %% http://tools.ietf.org/html/rfc3261#section-20.13
  process(fn, 'content-language', _Ignore) -> <<"Content-Language">>;
  process(p, 'content-language', Bin) ->
      {LangBin, Rest} = sip_binary:parse_token(Bin),
  