...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
The type of each element in the list.
using value_type = std::pair< string_view, string_view >;
The first string in the pair is the name of the parameter, and the second string in the pair is its value (which may be empty).