For some of my programs it would be nice to give the user some visual feedback about the created geometric elements or about elements that caused trouble. That would help to check program results or manually fix problems.
I know I can highlight elements from whithin my code. But it is not easy/intuitive for the user to unhighlight them or work with them later.
As far as I know it is not possible to select elements in the program without user interaction and keep them selected after program termination.