[This is preliminary documentation and subject to change.]
Server applications send this notification when an object or objects have been added to the selection within a container. This is appropriate when the number of newly selected items is very small.
The hwnd and idObject parameters of the WinEventProc callback function describe the container, and the idChild parameter is the child that was added to the selection.
Do not confuse object selection with object focus. For more information, see Accessible Object Selection and Focus.