alsa - Add support for media-libs/alsa-lib (Advanced Linux Sound Architecture)
bindist - Flag to enable or disable options for prebuilt (GRP) packages (eg. due to licensing issues)
custom-cflags - Build with user-specified CFLAGS (unsupported)
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
designer - Install the QWebEngineView plugin used to add widgets in dev-qt/designer forms that display web pages.
geolocation - Enable physical position determination
jumbo-build - Combine source files to speed up build process.