Telling emerge *NOT* to downgrade

The Linux distro I use is Gentoo and its software packages maintanance application is called Portage and is used through the command:

emerge [packageyouwannainstall]

By default, emerge installs the "stable" version of that package. But if you want a newer and less reliable versions of a package you can put

ACCEPT_KEYWORDS="~x86"

before that command. The problem is that when, after that, you tell Portage to update all your software to newer versions it may find, using the command

emerge --update world

, it still uses the default "stable" criteria, automatically downgrading any software you had previously installed or updated using ACCEPT_KEYWORDS="~x86". And if you use that before emerge --update world, it updates ALL your system to unstable versions.

So, until today, I had no idea of how to update my system with stable versions of my packages, only keeping the newer unstable versions I had previously installed. And I found out all you need to do is type:

emerge -uU world

hit Enter, sit back and enjoy the fun of fresh (and *only* fresh) stuff being installed. :-)