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

Calculating dependencies ... done!
Dependency resolution took 1.04 s (backtrack: 0/20).

[ebuild  N     ] x11-apps/sessreg-1.1.4::gentoo  134 KiB
[ebuild  N     ] x11-misc/slim-1.4.0::gentoo  USE="pam -branding" 518 KiB
[ebuild  N     ] x11-themes/slim-themes-1.2.3a-r7::gentoo  9822 KiB

Total: 3 packages (3 new), Size of downloads: 10473 KiB