From Xojo Documentation
| This item has been deprecated since version 2019r2 and should no longer be used.
Please use ListBox.RowSelectionType as a replacement.
Indicates the type of selection allowed via mouse gestures.
Use the following class constants to set the selection type:
|0||SelectionSingle||Single row selection|
|1||SelectionMultiple||Multiple row selection|
The default is single-row selection. If multiple row selection is on, a ListBox will handle Edit ↠ Select All menu item commands by default as long as the Select All menu item is named EditSelectAll.