docs: public static CharMatcher anyOf(final CharSequence sequence) {
      switch (sequence.length()) {
        case 0:
          return NONE;
        case 1:
          return is(sequence.charAt(0));
        case 2:
          return isEither(sequence.charAt(0), sequence.charAt(1));
        default:
          // continue below to handle the general case
      }
      // TODO(user): is it potentially worth just going ahead and building a precomputed matcher?
      final char[] chars = sequence.toString().toCharArray();
      Arrays.sort(chars);
      return new CharMatcher() {
        @Override public boolean matches(char c) {
          return Arrays.binarySearch(chars, c) >= 0;
        }
  
        @Override
        @GwtIncompatible("java.util.BitSet")
        void setBits(BitSet table) {
          for (char c : chars) {
            table.set(c);
          }
        }
  
        @Override public String toString() {
          StringBuilder description = new StringBuilder("CharMatcher.anyOf(\"");
          for (char c : chars) {
            description.append(showCharacter(c));
          }
          description.append("\")");
          return description.toString();
        }
      };
    }