[string.view.deduct]
27 Strings library [strings]
27.3 String view classes [string.view]
27.3.3 Class template basic_string_view [string.view.template]
27.3.3.3 Deduction guides [string.view.deduct]
template<class It, class End>
basic_string_view(It, End) -> basic_string_view<iter_value_t<It>>;
Constraints:
It satisfies contiguous_iterator.
End satisfies sized_sentinel_for<It>.
template<class R>
basic_string_view(R&&) -> basic_string_view<ranges::range_value_t<R>>;
Constraints: R satisfies ranges​::​contiguous_range.