code: public Set<String> getArgumentNames() {
          Set<String> result = new HashSet<String>();
          for (int partIndex = 0; (partIndex = nextTopLevelArgStart(partIndex)) >= 0;) {
              result.add(getArgName(partIndex + 1));
          }
          return result;
      }
docs: <strong>[icu]</strong> Returns the top-level argument names. For more details, see
  {@link #setFormatByArgumentName(String, Format)}.
  @return a Set of argument names