Selection should be implemented by UI components with children which are exposed by atk_object_ref_child
and get_n_children, if the use of the parent UI component
ordinarily involves selection of one or more of the objects corresponding to those Object
children - for example, selectable lists.
Note that other types of "selection" (for instance text selection) are accomplished a other ATK interfaces - Selection
is limited to the selection/deselection of children.
Determines if the current child of this object is selected Note: callers
should not rely on null or on a zero value for indication of whether AtkSelectionIface is implemented, they should use type
checking/interface checking macros or the atk_get_accessible_value convenience method.