$ libreoffice --version
 5.4.5.1 40m0(Build:1)

$ equery u app-office/libreoffice
[ Legend : U - final flag setting for installation]
[        : I - package is installed with flag     ]
[ Colors : set, unset                             ]
 * Found these USE flags for app-office/libreoffice-5.4.5.1:
 U I
 + + bluetooth                                   : Enable Bluetooth Support
 - - branding                                    : Enable Gentoo specific branding
 - - collada                                     : Enable Collada for rendering 3D models stored in
                                                   *.dae and *.kmz format
 + + cups                                        : Add support for CUPS (Common Unix Printing
                                                   System)
 + + dbus                                        : Enable dbus support for anything that needs it
                                                   (gpsd, gnomemeeting, etc)
 - - debug                                       : Enable extra debug codepaths, like asserts and
                                                   extra output. If you want to get meaningful
                                                   backtraces see https://wiki.gentoo.org/wiki/Proj
                                                   ect:Quality_Assurance/Backtraces
 - - eds                                         : Enable support for Evolution-Data-Server (EDS)
 - - gltf                                        : Use media-libs/libgltf for inserting 3D models
                                                   in the glTF format into presentations
 - - googledrive                                 : Enable support for remote files on Google Drive
 + + gstreamer                                   : Add support for media-libs/gstreamer (Streaming
                                                   media)
 + + gtk                                         : Add support for x11-libs/gtk+ (The GIMP Toolkit)
 - - gtk3                                        : Enable experimental gtk3 frontend
 - - java                                        : Add support for Java
 - - jemalloc                                    : Use dev-libs/jemalloc for allocations
 - - kde                                         : Add support for KDE (K Desktop Environment)
 - - libreoffice_extensions_nlpsolver            : LIBREOFFICE_EXTENSIONS option to build
                                                   non-linear solver for calc
 - - libreoffice_extensions_scripting-beanshell  : LIBREOFFICE_EXTENSIONS option to build beanshell
                                                   scripts parser
 - - libreoffice_extensions_scripting-javascript : LIBREOFFICE_EXTENSIONS option to build
                                                   javascript scripts parser
 - - libreoffice_extensions_wiki-publisher       : LIBREOFFICE_EXTENSIONS option to build mediawiki
                                                   integration
 - - libressl                                    : Use dev-libs/libressl instead of
                                                   dev-libs/openssl when applicable (see also the
                                                   ssl useflag)
 - - mysql                                       : Add mySQL Database support
 - - odk                                         : Build the Office Development Kit
 - - pdfimport                                   : Enable PDF import via the Poppler library
 - - postgres                                    : Add support for the postgresql database
 - - python_single_target_python2_7              : Build for Python 2.7 only
 - - python_single_target_python3_4              : Build for Python 3.4 only
 + + python_single_target_python3_5              : Build for Python 3.5 only
 - - python_single_target_python3_6              : Build for Python 3.6 only
 + + python_targets_python2_7                    : Build with Python 2.7
 - - python_targets_python3_4                    : Build with Python 3.4
 + + python_targets_python3_5                    : Build with Python 3.5
 - - python_targets_python3_6                    : Build with Python 3.6
 - - quickstarter                                : Build the system tray quickstarter
 - - 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
 - - vlc                                         : Use media-video/vlc for video embedding