Defstruct descriptor question

[kerry@ADS.COM (Kerry Koitzsch)]

Hello MCL experts:

I know you can get a defstruct's descriptor from its name,
i.e.
(defstruct mystruct a b c)
(setf desc (get 'mystruct 'ccl::\%defstruct)) --> descriptor

and that (elt desc 6) returns the PRINT-FUNCTION of the defstruct,
my question: whats in elt 0 through 5, and whats in 7 .....??

Second question: did this change between the MCL1.x(s) and  MCL2.0?
Sorry if this is an MCL FAQ. Thanks, kerry