Determines when a scroll bar will be visible.
Value | Symbolic name | Description |
| 0 | Gtk::POLICY_ALWAYS | The scrollbar is always visible. |
| 1 | Gtk::POLICY_AUTOMATIC | The scrollbar will appear and disappear as necessary. For example, when all of a GtkCList can not be seen. |
| 2 | Gtk::POLICY_NEVER | The scrollbar will never appear. |