The -selectmode option controls how many items the user can select at one time. In the single and browse mode, the user can select only one item at a time. In the multiple and extended mode, the user can select multiple items; the extended mode allows disjoint selections while the multiple mode does not.
Normally, the user selects the items using the mouse or the keyboard. You can find out which items the user has selected with the info selection method, which returns a list of the currently selected items. You can also set the selection using the selection set method. For example, the command .tlist selection set 3 selects the item whose index is 3. The command .tlist selection set 2 10 selects all the items at index 2 through 10. The method selection clear empties the selection.