/sys$common/syshlp/helplib.hlb DUMP, Qualifiers, /DESCRIPTOR  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DESCRIPTOR[=(option[,...])]

    Dumps the specified ISO 9660 volume descriptors in a formatted
    manner. If /NOFORMATTED is specified, block mode format is used.

    The descriptor options that you can specify are as follows:

    BOOT:n     Searches for the nth occurrence of a Boot Record.

    PVD:n      Searches for the nth occurrence of a Primary Volume
               Descriptor.

    SVD:n      Searches for the nth occurrence of a Supplementary
               Volume Descriptor.

    VPD:n      Searches for the nth occurrence of a Volume Partition
               Descriptor.

    VDST:n     Searches for the nth occurrence of a Volume Descriptor
               Set Terminator.

    If you specify only one option, you can omit the parentheses.

    ISO 9660 descriptors are specified by their ordinal position
    from the start of the volume, defaulting to 1 if they are not
    specified. The ISO 9660 volume is sequentially searched from
    the beginning of the volume descriptor set sequence to the end
    to find the specified descriptor and output it in a formatted
    manner.