+To get the class and instance, you can use +xprop+. After clicking on the
+window, you will see the following output:
+
+*xwininfo*:
+-----------------------------------
+WM_CLASS(STRING) = "irssi", "URxvt"
+-----------------------------------
+
+The first part of the WM_CLASS is the instance ("irssi" in this example), the
+second part is the class ("URxvt" in this example).
+
+Should you have any problems with assignments, make sure to check the i3
+logfile first (see http://i3wm.org/docs/debugging.html). It includes more
+details about the matching process and the window’s actual class, instance and
+title when starting up.
+