code: func (b *reportBuffer) mergeFrom(from *reportBuffer) {
  	b.droppedSpanCount += from.droppedSpanCount
  	b.logEncoderErrorCount += from.logEncoderErrorCount
  	if from.reportStart.Before(b.reportStart) {
  		b.reportStart = from.reportStart
  	}
  	if from.reportEnd.After(b.reportEnd) {
  		b.reportEnd = from.reportEnd
  	}
  
  	// Note: Somewhat arbitrarily dropping the spans that won't
  	// fit; could be more principled here to avoid bias.
  	have := len(b.rawSpans)
  	space := cap(b.rawSpans) - have
  	unreported := len(from.rawSpans)
  
  	if space > unreported {
  		space = unreported
  	}
  
  	b.rawSpans = append(b.rawSpans, from.rawSpans[0:space]...)
  
  	b.droppedSpanCount += int64(unreported - space)
  
  	from.clear()
  }
docs: // mergeFrom combines the spans and metadata in `from` with `into`,
  // returning with `from` empty and `into` having a subset of the
  // combined data.