Add utility to get widows attributes

xprop

Guides/i3.md

@@ -23,3 +23,7 @@ To get information :
 To adjust screen setup :
 
 `xrandr --output HDMI-0 --auto --above DP-0`
+
+## Filter windows
+
+To get informations used by filter, for example with `for_window`, use `xprop`.