code: public PatternTokenizer setIgnorableCharacters(UnicodeSet ignorableCharacters) {
          this.ignorableCharacters = (UnicodeSet) ignorableCharacters.clone();
          needingQuoteCharacters = null;
          return this;
      }
docs: Sets the characters to be ignored in parsing, eg new UnicodeSet("[:pattern_whitespace:]");
  @param ignorableCharacters Characters to be ignored.
  @return A PatternTokenizer object in which characters are specified as ignored characters.