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
jit - Enable just-in-time compilation for improved performance. May prevent use of some PaX memory protection features in Gentoo Hardened.
scripttools - Build the QtScriptTools module (requires QtWidgets)
test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)