debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
handbook - Enable handbooks generation for packages by KDE
kiosk - Enable kiosk mode by default (for use by small children or on a self-service host machine)
test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
