/usr/include/xfce4/ is in libxfce4util-dev 4.8.2-1.
This file is owned by root:root, with mode 0o755.
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/usr/include/xfce4/libxfce4util/
/usr/include/xfce4/libxfce4util/debug.h
/usr/include/xfce4/libxfce4util/i18n.h
/usr/include/xfce4/libxfce4util/libxfce4util-config.h
/usr/include/xfce4/libxfce4util/libxfce4util-enum-types.h
/usr/include/xfce4/libxfce4util/libxfce4util.h
/usr/include/xfce4/libxfce4util/utf8.h
/usr/include/xfce4/libxfce4util/util.h
/usr/include/xfce4/libxfce4util/xfce-desktopentry.h
/usr/include/xfce4/libxfce4util/xfce-fileutils.h
/usr/include/xfce4/libxfce4util/xfce-generics.h
/usr/include/xfce4/libxfce4util/xfce-i18n.h
/usr/include/xfce4/libxfce4util/xfce-kiosk.h
/usr/include/xfce4/libxfce4util/xfce-license.h
/usr/include/xfce4/libxfce4util/xfce-miscutils.h
/usr/include/xfce4/libxfce4util/xfce-posix-signal-handler.h
/usr/include/xfce4/libxfce4util/xfce-rc.h
/usr/include/xfce4/libxfce4util/xfce-resource.h
/usr/include/xfce4/libxfce4util/xfce-utf8.h