.DEFINE_IREG  X1    R5      ; X1 is integer register 5
           .UNDEFINE_REG X1            ; X1 is an identifier again
           .DEFINE_IREG  X1    7       ; X1 is integer register 7 -
 no
                                        ;  redefinition and no warning

            $ROUTINE F0                 ; Error: F0 is a register and
                                        ;  cannot be used as an
                                        ;  identifier
            .UNDEFINE_REG F0            ; F0 is no longer a register
            $ROUTINE F0                 ; Ok now