There are three Output Preview commands:
•Output Preview, which switches Output Preview on/off
•Output Preview Horizontal, which is enabled when Output Preview has been switched on. The command switches from a vertical split view to a horizontal split view. When the output preview becomes available in a horizontal split, the command automatically changes to Output Preview Vertical, which switches the split view back to a vertical split view.
•Refresh Output Preview, which immediately refresh the output preview with any changes in the design.