xa, xb, ya, yb
Append a new entry to the list of clean windows.
EXAMPLE
-------

0> addwin -1.5,1.0,-3.0,2
0>

PARAMETERS
----------

xa  -   The relative Right-Ascension of either edge of the new window.
xb  -   The relative Right-Ascension of the opposite edge to 'xa', of
        the new window.
ya  -   The relative Declination of either edge of the new window.
yb  -   The relative Declination of the opposite edge to 'ya', of the
        new window.

Coordinates should be specified with the same sign convention and
units as displayed in mapplot. (See help on the mapunits command).

CONTEXT
-------
Normally clean windows should be set with the cursor in the mapplot
command. Each new window added is appended to a list of clean windows
for use in clean. The addwin command provides a way to add windows
to the same list, but directly at the command line.

RELATED COMMANDS
----------------
mapplot - Allows adding and deleting windows with the cursor.
delwin  - Deletes all clean windows.
clean   - Cleans within the specified clean windows.