In [format.syn], there is no declaration for tuple formatter ([format.tuple]).
Given that it is an independent section like [format.range], should we add the something like the following to the <format>'s synopsis?

// [format.tuple], tuple formatter
template<class charT, formattable<charT>... Ts>
  struct formatter<pair-or-tuple<Ts...>, charT>;

Although the pair-or-tuple here is not very clear to me, even though it is described in [format.tuple] as follows:

For each of pair and tuple, the library provides the following formatter specialization where pair-or-tuple is the name of the template: