code: func New(recorder SpanRecorder) opentracing.Tracer {
  	opts := DefaultOptions()
  	opts.Recorder = recorder
  	return NewWithOptions(opts)
  }
docs: // New creates and returns a standard Tracer which defers completed Spans to
  // `recorder`.
  // Spans created by this Tracer support the ext.SamplingPriority tag: Setting
  // ext.SamplingPriority causes the Span to be Sampled from that point on.