multiple-value-setq assigns values to vars.
The form is evaluated,
and each var is assigned
to the corresponding value returned by that form.
If there are more vars than values returned,
nil is assigned to the extra vars.
If there are more values than vars,
the extra values are discarded.
If any var is the name of a symbol macro,
then it is assigned as if by setf. Specifically,
(multiple-value-setq (symbol1 ... symbolN) value-producing-form)
is defined to always behave in the same way as
(values (setf (values symbol1 ... symbolN) value-producing-form))
in order that the rules for order of evaluation and side-effects be consistent
with those used by setf.
See Section 188.8.131.52 VALUES Forms as Places.