code: func MaxSamplingRate(r int) TracerOption {
  	if r <= 0 {
  		panic("max sampling rate must be greater than 0")
  	}
  	return func(o *tracerOptions) *tracerOptions {
  		o.maxSamplingRate = r
  		return o
  	}
  }
docs: // MaxSamplingRate sets a target sampling rate in requests per second. Setting a
  // max sampling rate causes the middleware to adjust the sampling percent
  // dynamically.
  // SamplingPercent and MaxSamplingRate are mutually exclusive.