dh_installdeb automatically installs the following files from debian/ into
the DEBIAN directory:
The postinst, preinst, postrm, and prerm are handled specially: If a corresponding file named debian/package.script.debhelper exists, the contents of that file are merged into the script as follows: If the script exists, then anywhere in it that ``#DEBHELPER#'' appears, the text of the .debhelper file is inserted. If the script does not exist, then a script is generated from the .debhelper file. The .debhelper files are created by other debhelper programs, such as dh_installmenu(1), and are shell script fragments.
In V3 compatibility mode and higher, all files in the etc/ directory in a package will automatically be flagged as conffiles by this program, so there is no need to list them manually in package.conffiles.