docs: private static String formURI(String base, String append) {
          base = stripTrailingSlash(base);
          append = stripStartingSlash(append);
          if (append.startsWith("..")) {
              final String[] parts = append.split("/");
              for (final String part : parts) {
                  if ("..".equals(part)) {
                      final int last = base.lastIndexOf("/");
                      if (last != -1) {
                          base = base.substring(0, last);
                          append = append.substring(3, append.length());
                      } else {
                          break;
                      }
                  }
              }
          }
          return base + "/" + append;
      }