code: func (e *RawV4Event) ExtraHeaders() []byte {
  	begin := sizeOfBasicV4EventHeader
  	end := sizeOfBasicV4EventHeader + e.extraHeadersSize
  	return e.data[begin:end]
  }
docs: // RawV4Event's ExtraHeaders returns the extra header bytes associated to the
  // event.  NOTE: by default, the extra header length is not set and this returns
  // an empty byte slice.  Use SetExtraHeaderSize to specify the length.