The CALLED_BY function is a relationship function. It finds
    occurrences that have a CALLED_BY relationship between them.
    For example, if routine B is called by routine A, then these two
    occurrences are in a CALLED_BY relationship. In its most common
    form, the function format is as follows:

    CALLED_BY( <caller>, <callee>, DEPTH={<number> | ALL} )

    In this format, <caller> and <callee> can be any legal query
    expression, and <number> is a positive integer. A typical use
    of the function is to find those routines which are called by some
    specified routine. For example:

      FIND CALLED_BY( xyz, *, DEPTH=ALL )

    This query finds the full call tree below XYZ, where XYZ is some
    routine in the SCA database. In other words, this query finds all
    routines which are either directly or indirectly called by XYZ.

    The CALLED_BY function provides the power to return the exact call
    tree you want. The full format is as follows:

    CALLED_BY( [ END=<caller> ],
               [ BEGIN=<callee> ],
               [ DEPTH={<number> | ALL} ],
               [ RESULT=RESULT_KEYWORD ],
               [ TRACE=query_expression ] )

    In the previous format, <callee> and < caller> is any legal query
    expresion, <number> is a positive integer, RESULT_KEYWORD can
    be STRUCTURE, NOSTRUCTURE, ANY_PATH, BEGIN, or END, and QUERY_
    EXPRESSION is any legal query expression.

    For a full description of the CALLED_BY relationship, see the
    on-line help file SCACOMMANDS.