Return the starting position of the first occurrence of the specified substring, if such a substring can be found in this string (on or after the optionally specified position if such a position is specified) using CHAR_TRAITS::eq to compare characters, and return npos otherwise. The behavior is undefined unless the conversion from STRING_VIEW_LIKE_TYPE to bsl::basic_string_view<CHAR_TYPE, CHAR_TRAITS> does not throw any exception. Note that this behavior differs from the behavior implemented in the standard container, where the following noexcept specification is used: ` noexcept( std::is_nothrow_convertible_v<const T&, std::basic_string_view<CharT, Traits> >) `