On non-AmigaOS systems this attribute is only supported for the dataview
backend. When creating a treeview and Treeviewcolumn.Hide is
True, RapaGUI will automatically switch to the dataview backend.
If you don't specify this attribute at creation time but want to set it
later using moai.Set(), you have to explicitly request
a dataview widget by setting the Treeview.ForceMode attribute.