Normative ordering for modifier key combinations

When indicating valid key modifier combinations to users, is there a "correct" or normative order in which to describe them? For instance, if you wanted the user to press shift and control and alt and then press the F3 key, how would you write that:

SHIFT+ALT+CTRL+F3
ALT+CTRL+SHIFT+F3
CTRL+SHIFT+ALT+F3

?