My system environment configuration using nix and Home Manager.
After installing nix and home-manager link the home.nix to the location expected by Home Manager:
ln -s ~/location/nix-home/home.nix ~/.config/nixpkgs/home.nix
You'll want to at least update the home.username and home.homeDirectory attributes to be accurate for your user.
You can then run normal Home Manager workflow commands, home-manager edit, home-manager switch.
Some more comprehensive examples
Others can be found at the NixOS Wiki page for Home Manager.
https://github.com/SirVer/ultisnips/blob/master/doc/UltiSnips.txt
A line beginning with the keyword 'priority' sets the priority for all snippets defined in the current file after this line. The default priority for a file is always 0.