code: @SuppressWarnings({"MethodMayBeStatic"})
    protected void addAllInterningAndSuffixing(Collection<String> accumulator, Collection<String> addend, String suffix) {
      boolean nonNullSuffix = suffix != null && ! "".equals(suffix);
      if (nonNullSuffix) {
        suffix = '|' + suffix;
      }
      // boolean intern2 = flags.intern2;
      for (String feat : addend) {
        if (nonNullSuffix) {
          feat = feat.concat(suffix);
        }
        // if (intern2) {
        //   feat = feat.intern();
        // }
        accumulator.add(feat);
      }
    }
docs: Makes more complete feature names out of partial feature names, by
  adding a suffix to the String feature name, adding results to an
  accumulator
  
  @param accumulator The output features are added here
  @param addend The base set of features
  @param suffix The suffix added to each feature in the addend set