Scrivener 3 has a new feature called a copyholder which allows you to display the content of another document within the editor. Unlike the split screen Editor, the copyholder can only view a single file (document, image, etc) and doesn’t support group view modes (i.e. Scrivenings, Corkboard, or Outliner).
Viewing Documents in Multiple Copyholders with Split Screen
Speaking of split screen, you can have one copyholder for each editor pane, which means you can view up to four files at a time. Now you can put that swear jar full of pennies toward something more fun than an extra monitor.
Opening a Copyholder
To open a file in the copyholder, drag and drop it from the Binder to the Editor header while holding down the Option key, or select a file in the Binder and choose Navigate>Open>in Copyholder.
Changing the Copyholder Location
Control+click or right-click on the copyholder header bar to get a contextual menu where you can change the copyholder’s location, or go to View>Editor Layout>Copyholder Position>Left/Right/Top/Bottom.
Closing the Copyholder
To close a copyholder, click the X in the upper right corner of its header bar.
If you’d prefer to close the copyholder and open its document in a Quick Reference panel (a floating panel that allows you to view and edit a file), click the button to the left of the X on the copyholder header.