S T R U C T O R I Z E R - User Guide
Settings > Arranger index

The visibility of the scrollable Arranger index introduced by version 3.25-10 may be switched off or on via the menu item "Diagram => Show Arranger index?" (from version 3.25-11 on):

Menu Diagram with Show Arranger index selected

If enabled then the index tree of all currently arranged diagrams by groups will appear aside the work area unless the Arranger doesn't contain any diagrams or the Structorizer instance isn't associated (i.e. doesn't listen) to the Arranger:

Structorizer with Arranger index enabled

See the Arranger index section on the Arranger manual page for details how to work with the Arranger index.