code: func NewParsedV4EventReader(
  	reader EventReader,
  	parsers V4EventParserMap) EventReader {
  
  	return &parsedV4EventReader{
  		reader:       reader,
  		eventParsers: parsers,
  	}
  }
docs: // This returns an EventReader which applies the appropriate parser on each
  // raw v4 event in the stream.  If no parser is available for the event,
  // or if an error occurs during parsing, then the reader will return the
  // original event along with the error.