code: public void put(final String keys, final P value) {
          if (keys.matches(".*" + SIMPLE_CHARACTER_CLASS + ".*")) {
              int charClassStart = keys.indexOf('[', 0);
              final int charClassEnd = keys.indexOf(']', 1);
              String begin = keys.substring(0, charClassStart);
              for (; charClassStart < charClassEnd - 1; charClassStart++) {
                  char middle = keys.charAt(charClassStart + 1);
                  String end = keys.substring(charClassEnd + 1, keys.length());
                  put(begin + middle + end, value);
              }
          } else
              trie.put(keys, value);
      }
docs: Enables the use of simple character classes like 'a[agt][ac]'. Calls the
  method of {@link WildcardTrie} for further treatment.
  
  @param keys pattern of keys
  @param value value to associate with the key pattern