cpp/chrono/weekday/operator arith 2

@1-2@ Adds days to. The weekday value held in the result is computed by first evaluating and reducing it modulo 7 to an integer in the range [0, 6]. @3@ Subtracts days from. Equivalent to @4@ If and  are both, returns a std value  such that  is in the range [0, 6] and. Otherwise the returned value is unspecified.

Return value
@1-3@ A std holding a weekday value calculated as described above. @4@ A std representing the distance between and.