Doesn't it send up everything in the context directory, regardless of whether anything is ADDed? Because otherwise, the client would have to parse the Dockerfile also, to figure out what needs to be included in said context.

Ok, I've read through the code, and I agree, unless the argument is - the whole directory is always uploaded. I don't know where this stuff about absolute paths came from. I reviewed the code back at 0.5.3 and the behavior is the same, so it is not a recent change. I'll update the text to remove this nonsense.

If the argument is -, the context is automatically empty, isn't it?

thsre -> there :)

Doh!