Template:cpp/numeric/special functions/older impl note

Implementations that do not support C++17, but support ISO 29124:2010, provide this function if is defined by the implementation to a value at least 201003L and if the user defines  before including any standard library headers.

Implementations that do not support ISO 29124:2010 but support TR 19768:2007 (TR1), provide this function in the header and namespace.