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Right.  The question that Martin had was if you have some
mmap that has been mapped some offset into the large file,
and you do mmap.find(...), do you return an offset relative
to the file on disk, or relative to the mmap?

So if I have m = mmap.mmap(..., startoffset=1024,
length=1024), and I do m.find('X'), do I get some value
-1...1023 inclusive (-1 for not found), or do I get some
value 1024...2047 or -1?  I think it only makes sense to
return -1...1023, so that the return for .find() and other
operations are relative to the mmap, not the file.