nix-locate --help includes this line for the option --type:
-t, --type <TYPE> Only print matches for files that have this type. If the option is given multiple times, a file will be printed if it has any of the given types [possible values: r, x, d, s]
however, it's not explain what each of these values mean
nix-locate --help
includes this line for the option--type
:however, it's not explain what each of these values mean