I enable the following line in the file
/etc/apt/apt.conf.d/50unattended-upgrades according to the standard Debian wiki
to get security updates automatically.
Now I noticed that the line
is enabled by default. What is this for? I'm worried because this comes right after the lines with "stable" code-name, which might get my Jessie to upgrade to Stretch in the background. So what does this line do?