33 Concurrency support library [thread]

33.2 Requirements [thread.req]

33.2.3 Native handles [thread.req.native]

Several classes described in this Clause have members native_handle_type and native_handle.
The presence of these members and their semantics is implementation-defined.
[Note 1: 
These members allow implementations to provide access to implementation details.
Their names are specified to facilitate portable compile-time detection.
Actual use of these members is inherently non-portable.
— end note]