code: private int processSet(String regex, int i, StringBuilder result, UnicodeSet temp, ParsePosition pos) {
          try {
              pos.setIndex(i);
              UnicodeSet x = temp.clear().applyPattern(regex, pos, symbolTable, 0);
              x.complement().complement(); // hack to fix toPattern
              result.append(x.toPattern(false));
              i = pos.getIndex() - 1; // allow for the loop increment
              return i;
          } catch (Exception e) {
              throw (IllegalArgumentException) new IllegalArgumentException("Error in " + regex).initCause(e);
          }
      }
docs: ===== PRIVATES =====