Each module has its own Module Reference Index. Clicking on the Reference Index (<MODULE>R.IDX) hyperlink in a Module chapter of the Table of Contents will display the Module Reference Index for that module in the index pane. Clicking on any reference in the list will cause the Reference Index for that particular reference to be displayed in the content pane.
The Reference Index documents all the input and output references on CAD drawings. You can use the input and output references to track block outputs between drawings, following the "bubbles" yourself to verify that any output is linked to all the inputs that use it. You can also use the Reference Index to examine if the CAD drawings mention all the links in the drawing set. DBDOC audits input references for you by demanding that each input be driven by an output that it can find.