Defines a plotting area in absolute (device-independent) terms. The
xsize and ysize parameters are in cm; the locator index follows the
numeric keypad, i.e. 1=bottom left, 9=top right etc. The
locator index defaults to 5 (centre of plotting zone). To return to
(device-dependent) plotting zones use TZONE.
Subzones within the specified FRAME can be set using FRZONE.
