A thin wrapper around the Tk selection widget subcommand, used to adjust the selection within the spinbox. It has several forms depending on the first argument, such as selection('adjust', index), selection('clear'), selection('element', ?elem?), selection('from', index), selection('present'), selection('range', start, end) and selection('to', index). The selection_adjust(), selection_clear(), selection_element(), selection_from(), selection_present(), selection_range() and selection_to() methods wrap these forms.