C++ standard libraries extensions, version 3

From cppreference.com

Version 3 of the C++ Extensions for Library Fundamentals, defines the following new components for the C++ standard library, in addition to those defined in version 1 and version 2.

std::experimental::make_array and components merged into C++17/20 are excluded from LFTS v3.

Scope guard

Defined in header <experimental/scope>
wraps a function object and invokes it on exiting the scope
(class template)
wraps a function object and invokes it on exiting the scope through an exception
(class template)
wraps a function object and invokes it on exiting the scope normally
(class template)
universal RAII resource handle wrapper
(class template)

Feature test macros

Defined in header <experimental/scope>
__cpp_lib_experimental_scope
a value of at least 201902 indicates that the scope guard are supported
(macro constant)