{
  lib,
  ...
}:
let
  inherit (lib) types mkOption;
  inherit (types)
    attrTag
    attrsOf
    submodule
    submoduleWith
    deferredModule
    ;
in
{
  options = {
    runtime-environments = mkOption {
      type = attrsOf (attrTag {
        nixos = mkOption {
          type = submodule {
            options = {
              module = mkOption {
                description = "The NixOS module of the run-time environment";
                type = deferredModule;
              };
            };
          };
        };
      });
    };
    applications = mkOption {
      description = "Collection of NixOS modules, each implementing a Fediversity application";
      example.hello = {
        enable = true;
        module =
          { pkgs, ... }:
          {
            environment.systemPackages = [ pkgs.hello ];
          };
      };
      type = attrsOf (submoduleWith {
        description = "A Fediversity application";
        modules = [
          {
            options = {
              module = mkOption {
                description = "The NixOS module to compose into an operator's configuration";
                type = deferredModule;
              };
              components = mkOption {
                type = attrsOf (attrTag {
                  file-system-state = mkOption {
                    desciption = "files stored by the application";
                    type = attrsOf (submodule {
                      options.minSize = types.bytes;
                    });
                    database-state = mkOption {
                      desciption = "state stored in databases by the application";
                      type = attrsOf (submodule {
                        postgresql = mkOption {
                          desciption = "state stored in PostgreSQL by the application";
                          type = attrsOf (submodule {
                            options = {
                            };
                          });
                        };
                        key-val = mkOption {
                          desciption = "state stored in a key-value store by the application";
                          type = attrsOf (submodule {
                            options = {
                            };
                          });
                        };
                      });
                    };
                  };
                });
              };
            };
          }
        ];
      });
    };
  };
}