hon objects.

The create_tree_iter, set_user_data, invalidate_iters, iter_is_valid methods are
available to help manage Gtk.TreeIter objects and their Python object references.

GenericTreeModel manages a pool of user data nodes that have been used with iters.
This pool stores a references to user data nodes as a dictionary value with the
key being the integer id of the data. This id is what the Gtk.TreeIter objects
use to reference data in the pool.
References will be removed from the pool when the model is deleted or explicitly
by using the optional "node" argument to the "row_deleted" method when notifying
the model of row deletion.
Tz¿If True, strong references to user data attached to iters are stored in a dictionary pool (default). Otherwise the user data is stored as a raw pointer to a python object without a reference.)