warning about XML::SAX::Machines::SiteConfig and upgrades SiteConfig.pm is a Perl module which is supposed to be used for system configuration of the XML-SAX-Machines module, rather than changing things in ConfigDefaults. The problem is that on Debian systems, this file is installed in /usr/share/perl5, rather than /etc/perl, which means that any changes will be silently overwritten upon an upgrade, which would clobber a user's changes. The proposed fix for this is to add a documentation patch explaining this behaviour.
