If a row is expanded, the model of calling the
[callback@Gtk.TreeListModelCreateModelFunc] for the row's
item will be inserted after this row. If a row is collapsed,
those items will be removed from the model.
If the row is not expandable, this function does nothing.
Expands or collapses a row.
If a row is expanded, the model of calling the [callback@Gtk.TreeListModelCreateModelFunc] for the row's item will be inserted after this row. If a row is collapsed, those items will be removed from the model.
If the row is not expandable, this function does nothing.