std::chrono::year::operator+=, std::chrono::year::operator-=
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                    |   constexpr std::chrono::year& operator+=(const std::chrono::years& y) noexcept;  | 
(1) | (since C++20) | 
|   constexpr std::chrono::year& operator-=(const std::chrono::years& y) noexcept;  | 
(2) | (since C++20) | 
Adds or subtracts y.count() years from the year value.
1) Equivalent to *this = *this + y;
2) Equivalent to *this = *this - y;
Return value
A reference to this year after modification.
Notes
If the result would be outside the range [-32767, 32767], the actual stored value is unspecified.
Example
| This section is incomplete Reason: no example  | 
See also
|    increments or decrements the year  (public member function)  | |
   performs arithmetic on years  (public member function)  |