The SelectionType represents the most specific type of one or more objects that are
selected. As an example if one or more TableCell instances are selected in a Table, the selection type is SelectionType.TABLE_CELL. The TableCellRange can be
retrieved by using the Selection.getTableCellRange. The Table can be retrieved by
using the Selection.getPageElementRange and the Page can be retrieved from the
Selection.getCurrentPage.
To call an enum, you call its parent class, name, and property. For example,
SlidesApp.SelectionType.TEXT.