two version numbers on a kernel package?

[hendrik@topoi.pooq.com]

What does it mean when there are two version numbers on a package.  For 
example, one kernel package in the etch installer RC1 is

linux-image-2.6.17-2-486_2.6.17-9_i386.deb

Now clearly the 2.6.17-2-486

is part of the package name, making it possible to install more than one 
kernel package, should one decide to.

But then there's another version number, presumably to identify 
different patch levels as Debian makes its own adaptations to the 
kernel.

I would have expected this to result in versions like 
  linux-image-2.6.17-2-486_3_i386.deb
for the third patch to the upstream kernel.

But instead we get 
  linux-image-2.6.17-2-486_2.6.17-9_i386.deb
suggesting that there is more to the story.  What is the relationship 
between the 2.6.17-9 and the 2.6.17-2?  2.6.17-9 would offhand seem to 
be much later than 2.6.17-2.

For example, if someone were to speak of a 
bug or feature introduced in the 2.6.17-3, would I expect it to be 
present or absent in 2.6.17-2-486_2.6.17-9_i386?

Presumably, all there versions would precede 2.6.18, though.

-- hendrik