The listbox provides a scrollable list of text lines. The listbox supports selections of one or more lines.
Listbox widgets display a set of text lines in a scrollable display. The basic text unit is a line. There are operations to insert, select, and delete lines, but there are no operations to modify the characters in a line. As such, the listbox is suitable for displaying a set of choices, such as in a file selection dialog. By default a user can select one item from a listbox, but you can select multiple items by setting the selection mode attribute.
The lines in a listbox are indexed from zero. The keyword index
end addresses the last line. Other indices are described ...