code: function transform (chunk, output, fn) {
    if (!this._parserInit) init(this);
    debug('transform(%o bytes)', chunk.length);
  
    // XXX: old Transform stream API compat... remove at some point...
    if ('function' != typeof output) {
      output = this._parserOutput;
    }
  
    data(this, chunk, output, fn);
  }
docs: The `_transform()` callback function implementation.
  
  @api private