code: function Big5Encoder(options) {
      var fatal = options.fatal;
      /**
       * @param {Stream} stream Input stream.
       * @param {number} code_point Next code point read from the stream.
       * @return {(number|!Array.<number>)} Byte(s) to emit.
       */
      this.handler = function(stream, code_point) {
        // 1. If code point is end-of-stream, return finished.
        if (code_point === end_of_stream)
          return finished;
  
        // 2. If code point is an ASCII code point, return a byte whose
        // value is code point.
        if (isASCIICodePoint(code_point))
          return code_point;
  
        // 3. Let pointer be the index big5 pointer for code point.
        var pointer = indexBig5PointerFor(code_point);
  
        // 4. If pointer is null, return error with code point.
        if (pointer === null)
          return encoderError(code_point);
  
        // 5. Let lead be floor(pointer / 157) + 0x81.
        var lead = floor(pointer / 157) + 0x81;
  
        // 6. If lead is less than 0xA1, return error with code point.
        if (lead < 0xA1)
          return encoderError(code_point);
  
        // 7. Let trail be pointer % 157.
        var trail = pointer % 157;
  
        // 8. Let offset be 0x40 if trail is less than 0x3F and 0x62
        // otherwise.
        var offset = trail < 0x3F ? 0x40 : 0x62;
  
        // Return two bytes whose values are lead and trail + offset.
        return [lead, trail + offset];
      };
    }
docs: 12.1.2 big5 encoder 
  @constructor
  @implements {Encoder}
  @param {{fatal: boolean}} options