BS PD ISO/IEC TS 19571:2016

Since the extensions described in BS PD ISO/IEC TS 19571:2016 are experimental and not part of the C++ standard library, they should not be declared directly within namespace std. Unless otherwise specified, all components described in this technical specification either:

• modify an existing interface in the C++ Standard Library in-place,
• are declared in a namespace whose name appends ::experimental::concurrency_v1 to a namespace defined in the C++ Standard Library, such as std, or
• are declared in a subnamespace of a namespace described in the previous bullet, whose name is not the same as 2 an existing subnamespace of namespace std.