Byteranges with 206 partial content

Ari Luotonen writes:
	...
 > An additional feature is to say "give me a range if the document
 > hasn't changed, but if it has, send me the entire document".  Similar
 > to If-modified-since, but still quite different...  What would you
 > call such a header?
 > 

I'd use "last-modified", since what you're essentially saying is
"the document I received part of claimed to have been last-modified on <date>,
and now I want another piece of this document, unless it has changed since
that date."   Since we want some specific behavior in both cases -- 
in one case the whole document is returned, and in the other case only
a range -- it isn't quite right to use "if-not-modified-since.
(i.e. something happens if it *is* modified, too).  Last-modified would
reasonably encapsulate everything you need to say.

But I'd like to request that we break with tradition slightly, and as
an option allow something other than (or in addition to) last-modified
here: a checksum field, the rule being that you return in the request
the checksum received with the original fragment of the document.

 --Shel Kaphan