code: func NewWithOptions(opts Options) opentracing.Tracer {
  	rval := &tracerImpl{options: opts}
  	rval.textPropagator = &textMapPropagator{rval}
  	rval.binaryPropagator = &binaryPropagator{rval}
  	rval.accessorPropagator = &accessorPropagator{rval}
  	return rval
  }
docs: // NewWithOptions creates a customized Tracer.