disable-mask

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Bit mask indicating which control characters are not to be
    intercepted. The disable-mask argument is the address of an
    unsigned longword containing this bit mask.

    Each of the 32 bits corresponds to one of the 32 possible control
    characters. If a bit is set, the corresponding control character
    is no longer intercepted by the CLI. Currently, only bits 20 and
    25, corresponding to Ctrl/T and Ctrl/Y, are recognized.

    The following mask is defined in symbol libraries supplied by VSI
    to specify the value of disable-mask:

    Symbol          Hex Value     Function

    LIB$M_CLI_      %X'00100000'  Disables Ctrl/T
    CTRLT
    LIB$M_CLI_      %X'02000000'  Disables Ctrl/Y
    CTRLY

    If a set bit does not correspond to a character that the CLI can
    intercept, LIB$DISABLE_CTRL returns an error.

 old-mask

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       write only
    mechanism:    by reference

    Previous bit mask. The old-mask argument is the address of an
    unsigned longword into which LIB$DISABLE_CTRL writes the old bit
    mask. The old bit mask is of the same form as disable-mask and
    indicates those control characters that were previously enabled.
    It may therefore be given to LIB$ENABLE_CTRL to reinstate the
    previous condition.