“constant expression - one that can be evaluated at compile time. Deleted Functions (59), static_assert (115), Braced Init (224), constexpr Functions (257), constexpr Variables (302), Generalized PODs ’11 (431), initializer_list (554), User-Defined Literals (836), constexpr Functions ’14 (960), noexcept Specifier (1091)” (EMCppSfe 2021)