When an async request is acknowledged?

Hi,

I had a general question about web services. Sorry, it is not related to
CXF, but this is a so good community, maybe someone can help me:).

In case of an async web service call the receiver acknowledges the request
with an HTTP 202 usually. What is the semantics of this acknowledge:

1) We received the message, will process it later, and if no critical
failure happens, will send back an async response. The message might get
lost.

2) We received the message, validated it, so we can process it later. Will
send back an async response later if no critical failures. The message
might get lost.

3) We received, validated and persisted the request. So it wont be lost. We
will process it, and send back an async response later for sure.

4) ...

Does HTTP 202 has such a semantics, or does it leave the meaning open? Or
if a system uses async calls, should it decide on its own, what does
"acknowledge" mean?

Regards,
Ivan