This attribute can be used to set or get the active list entry. This will
always be between 0 and Listview.Entries-1 or the special value
-1 in case there currently is no active entry.
If you set this attribute the listview will automatically scroll the position
of the specified entry into view.
Besides an absolute index, you can also pass the following special values
here:
Off-
Clear selection.
Top-
Select first entry.
Bottom-
Select last entry.
Up-
Select previous entry.
Down-
Select next entry.
PageUp-
Move list cursor one page up.
PageDown-
Move list cursor one page down.
You can also set up a notification on this attribute to get notified
whenever the active entry is changed.