-.Ar keys
-is in the form of zero or more modifier keys
-(MOD, Mod1, Shift, etc.) and one or more normal keys
-(b, Space, etc.), separated by
+.Ar combo
+is in the form of zero or more modifier keys and/or special arguments
+(Mod1, Shift, MOD, etc.) and a normal key (b, Space, etc.)
+or a button (Button1 .. Button255), separated by