2.2.9 The meaning of "Pre-Depends"
dpkg always configures a package upon which another package
Depends before it configures the package that Depends on it. However,
dpkg normally unpacks archive files in arbitrary order,
independently of dependencies. (Unpacking consists of extracting files from
the archive file and putting them in the right place.) If, however, a package
Pre-Depends on another then the other package is unpacked and
configured before the one that Pre-Depends is even unpacked.  The use of this dependency is
kept to a minimum.