VMS Help SCA, SCA Topics, Glossary, occurrence_class  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    One of the attributes of an occurrence that tells you what kind of
    occurrence it is. The occurrence class indicates if an occurrence
    is a declaration, a reference, or another class. It also indicates
    what kind of declaration or reference it is. You can instruct SCA
    to show you only occurrences with a particular occurrence class
    using the OCCURRENCE= attribute selection. For example, you can
    ask for write references using OCCURRENCE=WRITE.