The App Trees Structure, that contain all the logical data of the
apptree.
popts
The packing options of the root widget.
visible_f
This boolean flag reflect the visible state of the apptree.
It is initially set to 1.
ctree
The current tree.
destroy_page_text
next_page_text
previous_page_text
cbs
Associative array containing the code associated with each callback
supported by the apptree. See the 'Callbacks' subsection for more
information about the available callbacks.