I've recently moved from using Cinnamon desktop environment to i3wm (quite a leap, I know). The first thing I've immediately noticed is that i3 doesn't handle external monitor connection automatically. I've spent some time googling around, and found out that all of the fixes suggest some form of manually connecting external output through xrandr (either writing xrandr --output … to the i3 config file; or running a script in the background, which checks if the external monitor is connected every 5 seconds, again, with xrandr— which is just bad programming).
At the same time, all the DEs that I've tried to that point handled external monitor connection automatically: you just plug in the monitor, and it switches on immidiately.
Then out of curiosity I've started to check other popular DEs, and noticed that xfce behaves the same way i3 does.
So there are my questions. How do KDE and Gnome handle external monitor connection automatically? And why i3 and xfce do not behave the same way? Perhaps, there is some sort of monitor-connection event, that is lacking in both i3 and xfce? And is it possible to implement for i3 the behaviour that is similar to KDE and Gnome?