Riddled by debian-policy 8.1.1 about ldconfig

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i am planning to offer my sponsor new versions of libburn, libisofs,
libisoburn. When looking for the needs to change Standards-Version from 3.9.8
to 4.1.0 i stumble over this statement in
  https://www.debian.org/doc/packaging-manuals/upgrading-checklist.txt

  8.1.1
     Shared libraries must now invoke "ldconfig" by means of triggers,
     instead of maintscripts.

The packages install libburn.so.4, libisofs.so.6, libisoburn.so.1.
But their current ./debian directories do not contain files preinst,
postinst, prerm or postrm. Further there is no text "ldconfig" in any
file underneath the current ./debian directories.

Is this an old omission of the packages ?

If so: What shall i read and/or do ?
(And why did the old packages work good enough to cause no complaints ?)

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Research difficulties:

The term "trigger" riddles me. Is it mentioned in the maintainer's guide ?
  https://www.debian.org/doc/manuals/maint-guide/

I find
  https://wiki.debian.org/DpkgTriggers
but cannot make a sufficient connection to the prescription in
upgrading-checklist.txt or to
  https://www.debian.org/doc/debian-policy/index.html#ldconfig

What is meant by "DEBIAN/triggers" in policy manual and man 5 deb-triggers ?
Is there supposed to be a "DEBIAN" directory under ./debian ?

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Have a nice day :)

Thomas