anchor.diff:      none;
   substr([C|S1], [C|S2], _MakeRel) ->
       substr(S1, S2, true);
  +substr([], [], true) ->
  +    {ok, "/"};
   substr([], S2, true) ->
       {ok, filename:join(S2)};
   substr(_S1, _S2, false) ->
  
positive.code: 
  rm_prefix_tesst_() ->
      Uri = occi_uri:parse("http://example.com:99/what/a/prefix/path/to/a/resource"),
      [
       ?_assert(rm_prefix(Uri, "/what/a/prefix") =:= #uri{path="path/to/a/resource"}),
       ?_assert(rm_prefix(Uri, "/what/a/prefix/") =:= #uri{path="path/to/a/resource"}),
  
negative.code: %%%
  -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;
  