Format: SET CURSOR top:bottom

 The SET CURSOR (abbreviated SE CU) command, used with screen editing,
 sets the limits within which the cursor is allowed to move without
 scrolling the screen.

 Top and bottom are the line numbers at the top of the screen and the
 bottom of the screen.  The line numbers must be in the range of 0 to 21,
 with 0 specifying the top of the screen and 21 the bottom.  The default
 setting is 7:14, allowing the cursor to move within the middle third of
 the screen.  If SET LINES is used to decrease the number of lines shown
 on the screen, the top and bottom of the cursor limits must be within
 the number of lines on the screen.