where expression is a variable that represents a Terminal Object
Remarks
When top and bottom screen margins are set (for example, by a text editor such as EDT or TPU, or with the DECSTBM function), the area within the margins is called the scrolling region. You cannot scroll outside of the scrolling region. By default, text that scrolls out of the scrolling region is not saved in display memory. If a scrolling region is set by a text editor, setting this property to true can cause display memory to fill quickly; every time you scroll your document down, text that scrolls off the top of the display is moved into display memory. For most situations, it's best to leave this property set to false. The default value is false.