FEATURES

The  variable contains a list of Portage features that the user wants enabled on the system, effectively setting Portage behavior.

The  variable is set by default via the system profile, but can be easily updated through. Since this is an incremental variable,  values can be added without directly  overriding the ones implemented through the system profile.

For more information, please see Portage Features in the Gentoo Handbook. For a complete list of available features, see man 5 make.conf.