root@x260 ~# equery u kwin
[ Legend : U - final flag setting for installation]
[        : I - package is installed with flag     ]
[ Colors : set, unset                             ]
 * Found these USE flags for kde-plasma/kwin-5.10.4-r1:
 U I
 - - 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
 - - gles2      : Use OpenGL ES 2 instead of full GL
 - - handbook   : Enable handbooks generation for packages by KDE
 - - multimedia : Enable effect video button in desktop effects KCM
 - - test       : Workaround to pull in packages needed to run with FEATURES=test. Portage-2.1.2 handles this internally, so don't set it in make.conf/package.use anymore
root@x260 ~#