anchor.diff:  %%%
   -spec add_prefix(uri(), string()) -> uri().
   add_prefix(#uri{path=Path}=Uri, Prefix) ->
  +    lager:debug("### add_prefix(~p, ~p)~n", [Path, Prefix]),
       case filename:split(Path) of
   	["/"|_P] ->
   	    Uri;
  
positive.code: %%% Remove prefix and make path relative
  %%%
  -spec rm_prefix(uri(), string()) -> uri().
  rm_prefix(#uri{path=Path}=Uri, Prefix) ->
      case substr(Prefix, Path) of
  	{ok, Path2} -> #uri{path=Path2};
  	none -> Uri
  
negative.code: 		  #uri{scheme=http, host="example.com", port=99, path="/what/a/prefix/path/to/a/resource"}),
       ?_assert(rm_prefix(Uri, "/what/a/prefix") =:= 
  		  #uri{scheme=http, host="example.com", port=99, path="/what/a/prefix/path/to/a/resource"}),
       ?_assert(rm_prefix(Uri, "/") =:= #uri{path="what/a/prefix/path/to/a/resource"}),
       ?_assert(rm_prefix(Uri2, "/a/long/prefix") =:= #uri{path="/resource"}),
       ?_assert(rm_prefix(Uri2, "/resource/") =:= #uri{path="/resource"})
      ].
      
  -endif.
  