anchor.diff:  * If `spring-cloud-sleuth-zipkin` is on the classpath, the app generates and collects Zipkin-compatible traces.
   By default, it sends them over HTTP to a Zipkin server on localhost (port 9411).
   You can configure the location of the service by setting `spring.zipkin.baseUrl`.
  -** If you depend on `spring-rabbit` or `spring-kafka`, your app sends traces to a broker instead of HTTP.
  -**
  +** If you depend on `spring-rabbit`, your app sends traces to a RabbitMQ broker instead of HTTP.
  +** If you depend on `spring-kafka`, and set `spring.zipkin.sender.type: kafka`, your app sends traces to a Kafka broker instead of HTTP.
   
   CAUTION: `spring-cloud-sleuth-stream` is deprecated and should no longer be used.
   
  
positive.code: [source,java]
  ----
  Span initialSpan = this.tracer.nextSpan().name("span").start();
  try (Tracer.SpanInScope ws = this.tracer.withSpanInScope(initialSpan)) {
      ExtraFieldPropagation.set("foo", "bar");
      ExtraFieldPropagation.set("UPPER_CASE", "someValue");
  }
  ----
  
  
negative.code: If you want to use RabbitMQ or Kafka instead of HTTP, add the `spring-rabbit` or `spring-kafka` dependency.
  The default destination name is `zipkin`.
  
  If using Kafka, you must set the property `spring.zipkin.sender.type` property accordingly:
  
  [source,yaml]
  ----
  spring.zipkin.sender.type: kafka
  ----
  
  CAUTION: `spring-cloud-sleuth-stream` is deprecated and incompatible with these destinations.
  
  If you want Sleuth over RabbitMQ, add the `spring-cloud-starter-zipkin` and `spring-rabbit`
  