/sys$common/syshlp/helplib.hlb CMS, SHOW, CLASS, Qualifiers, /OCCLUDE[=option,...]  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Controls whether CMS selects the first instance of the specified
    object, or all instances of the specified object in the library
    search list. The options field contains one or more keywords
    associated with the name of the object. The options field can
    contain the following keywords:

       ALL--equivalent to CLASS
       CLASS (D)
       NOCLASS
       NONE--equivalent to NOCLASS

    You can specify either ALL, NONE, or the [NO]CLASS keyword.

    By default, CMS performs occlusion for all objects; that is, CMS
    selects only the first occurrence of a specified object.