With tag_invoke #2228, we can provide customizations for standard types.

I'm thinking of:

• vector
• map
• deque
• list
• forward_list
• set
• multiset
• multimap
• unordered_set
• unordered_map
• unordered_multiset
• unordered_multimap
• stack
• queue
• priority_queue
• flat_set
• flat_map
• flat_multiset
• flat_multimap
• span
• unique_ptr
• smart_ptr
• atomic
• optional
• expected<T, E>
• filesystem::path
• chrono::duration
• pair
• tuple
• ...

Honestly, it's the opposite of std::formatter<...> customizations.

Felt like half a day of work when I started typing, but now it sounds like a whole week of work :)