What is the purpose of features.h header?

Question

What is the purpose of the features.h header? Why and when can it be used in my code?

Does it define source features supported by the system? Or does i

Answer 1

From features.h File Reference

Defines on whether to include algorithm variants. Less variants reduce executable size and compile time. This file is a GNU parallel extension to the Standard C++ Library.

So this file will include some algorithm listed in the reference page.