The following situations involving setf of apply must be supported:
In all three cases, the element of array designated by the concatenation of subscripts and more-subscripts (i.e., the same element which would be read by the call to apply if it were not part of a setf form) is changed to have the value given by new-element. For these usages, the function name (aref, bit, or sbit) must refer to the global function definition, rather than a locally defined function.
No other standardized function is required to be supported, but an implementation may define such support. An implementation may also define support for implementation-defined operators.
If a user-defined function is used in this context, the following equivalence is true, except that care is taken to preserve proper left-to-right evaluation of argument subforms:
(setf (apply #'name arg*) val) == (apply #'(setf name) val arg*)