anchor.diff:          403 -> <<"Forbidden">>;
           404 -> <<"Not Found">>;
           405 -> <<"Method Not Allowed">>;
  +        406 -> <<"Not Acceptable">>;
           407 -> <<"Proxy Authentication Required">>;
           408 -> <<"Request Timeout">>;
           410 -> <<"Gone">>;
  +        412 -> <<"Conditional Request Failed">>;
           413 -> <<"Request Entity Too Large">>;
           414 -> <<"Request-URI Too Long">>;
           415 -> <<"Unsupported Media Type">>;
           416 -> <<"Unsupported URI Scheme">>;
  +        417 -> <<"Unknown Resource Priority">>;
           420 -> <<"Bad Extension">>;
           421 -> <<"Extension Required">>;
  +        422 -> <<"Session Interval Too Small">>;
           423 -> <<"Interval Too Brief">>;
  +        428 -> <<"Use Identity Header">>;
  +        429 -> <<"Provide Referrer Identity">>;
  +        436 -> <<"Bad Indentity-Info">>;
  +        437 -> <<"Unsupported Certificate">>;
  +        438 -> <<"Invalid Identity Header">>;
           480 -> <<"Temporarily Unavailable">>;
           481 -> <<"Call/Transaction Does Not Exist">>;
           482 -> <<"Loop Detected">>;
  
positive.code:         488 -> <<"Not Acceptable Here">>;
          491 -> <<"Request Pending">>;
          493 -> <<"Undecipherable">>;
          500 -> <<"Server Internal Error">>;
          501 -> <<"Not Implemented">>;
          502 -> <<"Bad Gateway">>;
  
negative.code:         504 -> <<"Server Time-out">>;
          505 -> <<"Version Not Supported">>;
          513 -> <<"Message Too Large">>;
          580 -> <<"Precondition Faillure">>;
          600 -> <<"Busy Everywhere">>;
          603 -> <<"Decline">>;
          604 -> <<"Does Not Exist Anywhere">>;
          606 -> <<"Not Acceptable">>;
          _ -> <<"Unknown Code">>
      end.
  
  
  %% @private
  gen_opts(Opts) ->
  