As part of the Listbox widget, several choices exist for the way you can select items in the Listbox. You can have it so only one item at a time can be selected (emulating Radiobuttons) or you can have many different contiguous or noncontiguous items selected (emulating Checkbuttons). You control this behavior with the -selectmode option.
The possible select modes are "browse", "single", "multiple", or "extended". The default mode is "browse".
The -selectmode feature on Windows 95 does not allow the "multiple" selection mode, it behaves the same as "single" mode. On Unix and Windows NT, "multiple" mode works correctly.
When you select an item in a Listbox, by default it is made available as an X selection (meaning you can cut and paste it like any X selection in any window). Though this doesn't do anything with the clipboard on Win32 systems, it still affects the selection in multiple Listboxes. Items can be selected in only one Listbox at a time, even if you have more than one Listbox. The option -exportselection controls this. Use -exportselection => 0 to allow items to be selected in more than one Listbox at the same time.