semantics of dpkg-* configuration file backups

[Malte Forkel <malte.forkel@berlin.de>]

Hi,

When upgrading a package, the user can specify how a configuration file
should be handled that has been modified on the local systems.

Depending on the user's choice, a file with the extension dpkg-old,
dpkg-new or dpkg-dist might be created besides the configuration file.
Could someone please explain the semantics of these files? I.e., what
are the conditions for each of them to get created, what does each of
them contain?

Thanks in advance,
Malte