Etc portage package unmask needs updating
If so changing the sequence and installing the boot loader and testing boot can be performed before the gentoo system gets installed.With efi lots of options exist as not use a boot loader at all, use grub or an other installer, have other efi apps installed, use the old fashion MBR boot process. This might be necessary just during installation since the RAM must share both the life filesystem and the the RAM required to run the applications.The program On of the fundamental concepts of Gentoo is that the packages are not directly installed into the system.They are first installed in a temporary location and then copied (merged) file by file to the real system.If not, then the system will get sooner or later errors and requires troubleshooting. Virtual packages allow the use of different implementations for the same purpose.
You as system administrator can just (soft) mask them.On the other side you as system administrator can unmask hard masked packages and unmask unstable packages (packages under test).In the worst case a package is masked and unstable.Therefore in the future the line gets obsolete when newer stable versions are in portage and therefore the line can be wiped out.Alternatively to the echo command the file Masked packages are different from unstable packages.
It happens that packages depending on the ones you like to install fail during updates and you like to re-emerge such packages manually. If you don't use these options, then the world file collects all trouble packages and you will not get rid of them in the future. Unfortunately the same verb mask is used for two different things and creates therefore confusion.