The Preferences dialog provides the following options.
The Use AutoComplete check box in the Display Options group on the Editor Options sheet controls whether the feature is enabled. The feature is on, by default.
The Ctrl+Space key binding on the Editor Key Bindings sheet is the key sequence to manually invoke the AutoComplete list box based on the current cursor location.
The Ctrl+R key binding on the Editor Key Bindings sheet is the key sequence to toggle the display of RootSchema entities in the AutoComplete list box. For details, see "Toggling the Display of RootSchema Entities", later in this document.