gedit as examples. Open a terminal and run:
apt-cache show evince | grep Conflicts
apt-cache show evince | grep Breaks
This pair of commands will tell you if
evince breaks or conflicts with something else. In my case I get
$ apt-cache show evince | grep Conflicts
$ apt-cache show evince | grep Breaks
evince conflicts with
evince-gtk that means they shouldn't be installed at the same time (APT will complain if this ever happens).
In my case
evince doesn't declare to break any package so let's skip to
gedit. Now, run
$ apt-cache show gedit | grep Conflicts
$ apt-cache show gedit | grep Breaks
Breaks: gedit-plugins (<< 2.91)
As you can see
gedit does not conflict with anyone. Nonetheless, it does break the package called
gedit-plugins for versions strictly less than
2.91. That means
gedit-plugins most be more recent than this version to work correctly with
gedit and in particular APT will refuse to install
gedit unless you remove
gedit-plugins (<< 2.91) first.
Notice that even though the
gedit-plugins in the official repositories are recent enough, you might want to download (from
github maybe) a particular GEdit plugin that is older, this line serves you as a remainder that this older version should not work with the current GEdit version.
For more details about package relationships (and the official definitions of Breaks and Conflicts) refer to Debian Policy Manual - Chapter 7.