code: public Token scanHexDecimal() {
          int length = HEX_BEGIN_SYMBOL_LENGTH;
          if ('-' == charAt(offset + length)) {
              length++;
          }
          while (isHex(charAt(offset + length))) {
              length++;
          }
          return new Token(Literals.HEX, input.substring(offset, offset + length), offset + length);
      }
docs: scan hex decimal.
  
  @return hex decimal token