IMHO it's unfortunate that the grammar for parameter-declaration-clause is so mixed up at the moment. It has:

  parameter-declaration-clause:

    parameter-declaration-list_opt ..._opt

    parameter-declaration-list , ...

where the first production handles all of

  void f()

  void f(int)

  void f(int x)

  void f(...)

  void f(int...) // deprecated, equivalent to f(int,...)

  void f(auto...)

  void f(int x...) // deprecated, equivalent to f(int,...)

  void f(auto x...) // deprecated, equivalent to f(auto,...)

It would be so much cleaner to rewrite the grammar as

    parameter-declaration-list ...

where the fourth production is deprecated and the first three are not.

I admit I'm thinking about messy grammar mainly because of how much time I just put into studying the messy `friend` grammar and trying to disentangle it for "Variadic Friends." There's certainly a lot of precedent for the Committee's preferring "short and messy" over "long and clean," and concretely in this case, sadly, I think it would distract and slow down the paper if you asked to clean up the grammar at the same time.

Hmm, I wonder whether cleaning up this particular grammar could be done editorially! That obviously wasn't on the table for `friend`, but might be doable for something this small and self-contained.

 –Arthur