pool to dists assocation?

[Peter Michaux <petermichaux@gmail.com>]

Hi,

When I look at http://ftp.us.debian.org/debian/pool/main/a/apache2/ ,
I see the versions of apache2 for wheezy and jessie together in the
same directory. When the repository Packages index files are created,
how does apt-ftparchive know to put
apache2.2-bin_2.2.22-13+deb7u1_amd64.deb into
http://ftp.us.debian.org/debian/dists/wheezy/main/binary-amd64/Packages.gz
but put apache2.2-bin_2.4.9-1_amd64.deb into
http://ftp.us.debian.org/debian/dists/jessie/main/binary-amd64/Packages.gz
? Using dpkg --info for these two packages, I don't see what
information is used about the package so that dpkg-ftparchive knows
with which distribution to associate each package.

Thanks,
Peter