code: func AnnotateSpanWithChordInfo(span opentracing.Span, chord *tasks.Chord, sendConcurrency int) {
  	// tag the span with chord specific info
  	span.SetTag("chord.callback.uuid", chord.Callback.UUID)
  
  	// inject the tracing span into the callback signature
  	chord.Callback.Headers = HeadersWithSpan(chord.Callback.Headers, span)
  
  	// tag the span for the group part of the chord
  	AnnotateSpanWithGroupInfo(span, chord.Group, sendConcurrency)
  }
docs: // AnnotateSpanWithChordInfo ...