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

Calculating dependencies ... done!
Dependency resolution took 1.01 s (backtrack: 0/20).

[ebuild  N     ] x11-libs/libXdamage-1.1.7::gentoo  260 KiB
[ebuild  N     ] x11-libs/libXcomposite-0.4.7::gentoo  USE="-doc" 267 KiB
[ebuild  N     ] x11-misc/xcompmgr-1.1.10::gentoo  131 KiB

Total: 3 packages (3 new), Size of downloads: 656 KiB