Member set functions generate a list of members that is based on a member you specify. For example, the @IDESCENDANTS function generates a list of all the descendants of a specified member. When you use a member set function in a formula, Essbase generates a list of members before calculating the formula.
In the following example, using the @IDESCENDANTS command on the member Total Expenses generates a list of these members—Total Expenses, itself, and its descendants, which are Marketing, Payroll, and Misc:
@IDESCENDANTS("Total Expenses");