Library /sys$common/syshlp/lse$clihelp.hlb RESERVE, Qualifiers, /GENERATION  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /GENERATION[=generation-exp]

    Specifies the generation of the element to reserve. If you do
    not specify a value, LSE assumes you have specified generation
    "1+" (the generation-exp parameter must be enclosed in quotation
    marks if nonalphanumeric characters are present). If you omit
    the qualifier altogether, LSE uses the specified or default value
    from the command SET CMS/GENERATION to determine the generation to
    reserve.