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

Calculating dependencies ... done!
Dependency resolution took 1.00 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/set_opacity-1.0-r1::gentoo  5 KiB

Total: 3 packages (3 new), Size of downloads: 531 KiB