<< Actually, I think it's out-of-scope for the Content-Disposition document
<< to define what happens when the header is not present.
Another way to look at it however, is that the Content-Disposition spec is
completing part of the MIME spec (and hence could potentially be labled
"MIME Part 3", but that's another article). Since the MIME spec essentially
implies that the parts are currently equivalent to what this spec calls
"inline", then I don't see any problem with this being a >>clarification<< of
the MIME spec. Hence, it is perfectly reasonable for it to specify what it
means for the lack of this header to mean.