In 5d Document References states the following:
By clicking on the “+” button, you can choose to add a reference to a file on disk or you can select a document inside the project. You can also drag documents from within the project you are working in,Windows Explorer, or the URL from a browser address field, into the references table. Double-clicking on the icon of a reference will open it: external references open in their default application; internal references open inside Scrivener. Note that, as with notes, you can store references at the document or project level—click on the bar where it says “Document References” to flip between Document References (which are specific to the current document) and Project References (which can be viewed from any document).
I Doubled Clicked on the icon for Step 7: End of part one. The bottom of the main editor area splits and Step 6: End of part one is displayed. Looks like the Reference needs the Step number needs to be changed. I added Step 2 to the documents references and selected it and it displayed properly.
There was no instruction as to how to get the split screen to go back to whole in this section.