The focused element is not in the tree. It gets the number after the tree, a new
one on every read, and that number shows only in the focus line.
== read
a window
.b button
@z text field Search
== want
Window: "Main", App: App.
0 window
	1 button

The focused UI element is 2 text field Search
== read
a window
.b button
.c text new
@z text field Search
== want
<HEADER>
+	2 text new
The focused UI element is 3 text field Search
== end
