# emerge -av xorg-x11

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     UD] x11-base/xorg-x11-7.1 [7.2] 0 kB

Total: 1 package (1 downgrade), Size of downloads: 0 kB

Would you like to merge these packages? [Yes/No]

and /etc/portage/package.keyword:
#Xorg 7.2
#=x11-base/xorg-x11-7.2 ~x86
#=x11-libs/libXScrnSaver-1.1.2 ~x86
#=app-doc/xorg-docs-1.4 ~x86
#=x11-apps/xauth-1.0.2 ~x86
#=x11-libs/libXcursor-1.1.8 ~x86
#=x11-libs/libXfixes-4.0.3 ~x86
#=x11-base/xorg-server-1.2.0-r1 ~x86
#=x11-libs/libdrm-2.3.0 ~x86
#=x11-libs/libXfont-1.2.7 ~x86
#=media-libs/mesa-6.5.2-r1 ~x86
#=x11-apps/mesa-progs-6.5.2
#=x11-apps/xinit-1.0.3-r1 ~x86
#=x11-libs/libXcomposite-0.3.1 ~x86
#=x11-apps/xmodmap-1.0.2 ~x86
#=x11-libs/libXdamage-1.1 ~x86
#=x11-proto/damageproto-1.1.0 ~x86
#=x11-libs/libSM-1.0.2 ~x86
#=x11-libs/libXv-1.0.3 ~x86