The occurrence class is an attribute of an occurrence that
    identifies the type of occurrence. The occurrence class indicates
    if the occurrence is a declaration, a reference, or one of the
    other classes in the list that follows. If the occurrence class is
    a declaration or reference, the occurrence class indicates what
    type of declaration or reference it is.

    The format for the occurrence class attribute is as follows:

    OCCURRENCE=(keyword[,keyword...])

    The occurrence class can be one of the following keywords:

    Declarations

    o  PRIMARY - most significant declaration

    o  ASSOCIATED - associated declaration

    o  DECLARATION - primary or associated

    References

    o  READ, FETCH - fetch of a symbol value

    o  WRITE, STORE - assignment of a symbol value

    o  ADDRESS, POINTER - reference to the location of a symbol

    o  CALL - call to a routine or macro

    o  COMMAND_LINE - command line file reference

    o  INCLUDE - source file include referenece

    o  PRECOMPILED - precompiled file include referenece

    o  OTHER - any other kind of reference (such as a macro expansion
       or use of a constant)

    o  REFERENCE - any of the preceding values

    Other Occurrence Classes

    o  EXPLICIT - explicitly declared

    o  IMPLICIT - implicitly declared

    o  VISIBLE - occurrence appears in the source

    o  HIDDEN - occurrence does not appear in the source

    o  COMPILATION_UNIT - the declaration that contains all
       occurrences in a particular compilation unit

    The previous keywords are SCA terms. For information on
    corresponding language-specific terms, request help for the
    appropriate language table (for example, FORTRAN_ATTRIBUTES_TABLE)
    under the Getting_Started help topic.

    An example using the occurrence class attribute follows:

      FIND OCCURRENCE=PRIMARY

    This query finds all PRIMARY occurrences of declarations.