code: public final Flux<T> subscriberContext(Context mergeContext) {
  		return subscriberContext(c -> c.putAll(mergeContext));
  	}
docs: Enrich a potentially empty downstream {@link Context} by adding all values
  from the given {@link Context}, producing a new {@link Context} that is propagated
  upstream.
  <p>
  The {@link Context} propagation happens once per subscription (not on each onNext):
  it is done during the {@code subscribe(Subscriber)} phase, which runs from
  the last operator of a chain towards the first.
  <p>
  So this operator enriches a {@link Context} coming from under it in the chain
  (downstream, by default an empty one) and makes the new enriched {@link Context}
  visible to operators above it in the chain.
  
  @param mergeContext the {@link Context} to merge with a previous {@link Context}
  state, returning a new one.
  
  @return a contextualized {@link Flux}
  @see Context