I am on the current master branch. The standard-vtable-fields is "pwuhuhpwphuhuhuh" on my system and something similar in the Reference Manual. In particular, it contains the permission letter "h", but I find no explanation in the manual what that means.
Section 6.6.18.1 (Vtables) just mentions: "It used to be that the second letter for each field was a permission code, such as ‘w’ for writable or ‘r’ for read-only." And that read-only has become depriciated. At the end of section 6.6.18.4 (Meta-Vtables) is an example: (define* (make-vtable fields #:optional printer) (make-struct/no-tail <standard-vtable> (make-struct-layout fields) printer)) Without information on "h", I was not able to make sense of the fact, that fields with permission "h" somehow seem to be skipped by make-struct/no-tail when processing the two init values. In particular, for some reason, the value of printer is put into field 3 of the new structure and not in field 1, almost certainly somehow because fields 1 and 2 have "h". "h" should be documented.