code: func Extract(ctx context.Context) Tags {
  	t, ok := ctx.Value(ctxMarkerKey).(Tags)
  	if !ok {
  		return NoopTags
  	}
  
  	return t
  }
docs: // Extracts returns a pre-existing Tags object in the Context.
  // If the context wasn't set in a tag interceptor, a no-op Tag storage is returned that will *not* be propagated in context.