Huh. There simply aren't that many C++ compilers in the world that matter... who is working with a C++11 compiler, but doesn't have at least C++17? (The core problem with C++20 is that support is still spotty: like, I am waiting with baited breadth for clang to finally get around to P1091R3/P1381R1... they list it as "partial", but it feels like "not even started".)