SYNTAX            : ARG :W REG

RESULTING ARGUMENT: None

FUNCTION          : Make the register immediately following the command a
                    read-only register (or, depending on the argument,
                    revoke the read-only status).

                    A read-only register is protected against the following
                    occurrences:
                    - Switching into the register
                    - Redefining function key (if function key register)
                    - Redefining register as macro
                    - changing register type (numeric <-> string)
                    - changing register content
                    - inadvertent exit of TV (except by CTRL_C or -;h)

ARGUMENT          :  1 (protect)
                    -1 (revoke protection)

DEFAULT           :  1

NOTE 1            : Exiting TV when protected registers exist is only
                    possible via the CTRL_C-command or the -;h-command. All
                    other actions that usually terminate TV will now result
                    in a read-only register error message. Since this in
                    itself is not very helpful, be sure that
                    - The Display Messages setting is ON ( 2 CTRL_X)
                    - The Extended errors  setting is ON (27 CTRL_X)
                    The register which is the cause is then shown along with
                    the error.

NOTE 2            : A protected register can be pushed onto the associated
                    stack. An unprotected, cleared register is put in its
                    place. However, when the register is popped back, the
                    protection will still be in place.

7.0:
NOTE 3            : To access the register as an array, a subscript can be
                    used.

MATRIX