The docs suggest that the causation ID and the correlation ID exist:
Every stream in the event store has metadata associated with it. The Event Store itself supports some values being set in the metadata and you can write your own additional data into stream metadata if you wish (such as how often to snapshot for your own code). All names starting with $ are however a reserved space for internal settings.
I haven’t seen a reference to how and where they are written.
How do I find out how to format an HTTP Post so that causation ID and/or correlation ID are written. Also, how are these data read?
As an aside, it seems like the docs are written for an audience that is starting with some pre-knowledge of the product.