diff --git a/lib/types.nix b/lib/types.nix
index a7f9bf1946e6..7276f9af9fee 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -6,7 +6,7 @@ with import ./attrsets.nix;
 with import ./options.nix;
 with import ./trivial.nix;
 with import ./strings.nix;
-with {inherit (import ./modules.nix) mergeDefinitions; };
+with {inherit (import ./modules.nix) mergeDefinitions filterOverrides; };
 
 rec {
 
@@ -166,6 +166,23 @@ rec {
         substSubModules = m: loaOf (elemType.substSubModules m);
       };
 
+    # List or element of ...
+    loeOf = elemType: mkOptionType {
+      name = "element or list of ${elemType.name}s";
+      check = x: isList x || elemType.check x;
+      merge = loc: defs:
+        let
+          defs' = filterOverrides defs;
+          res = (head defs').value;
+        in
+        if isList res then concatLists (getValues defs')
+        else if lessThan 1 (length defs') then
+          throw "The option `${showOption loc}' is defined multiple times, in ${showFiles (getFiles defs)}."
+        else if !isString res then
+          throw "The option `${showOption loc}' does not have a string value, in ${showFiles (getFiles defs)}."
+        else res;
+    };
+
     uniq = elemType: mkOptionType {
       inherit (elemType) name check;
       merge = mergeOneOption;
diff --git a/nixos/modules/config/fonts/fontconfig.nix b/nixos/modules/config/fonts/fontconfig.nix
index 922a9cf961df..be6662decea6 100644
--- a/nixos/modules/config/fonts/fontconfig.nix
+++ b/nixos/modules/config/fonts/fontconfig.nix
@@ -108,10 +108,8 @@ with lib;
         subpixel = {
 
           rgba = mkOption {
-            type = types.string // {
-              check = flip elem ["rgb" "bgr" "vrgb" "vbgr" "none"];
-            };
             default = "rgb";
+            type = types.enum ["rgb" "bgr" "vrgb" "vbgr" "none"];
             description = ''
               Subpixel order, one of <literal>none</literal>,
               <literal>rgb</literal>, <literal>bgr</literal>,
@@ -120,10 +118,8 @@ with lib;
           };
 
           lcdfilter = mkOption {
-            type = types.str // {
-              check = flip elem ["none" "default" "light" "legacy"];
-            };
             default = "default";
+            type = types.enum ["none" "default" "light" "legacy"];
             description = ''
               FreeType LCD filter, one of <literal>none</literal>,
               <literal>default</literal>, <literal>light</literal>, or
diff --git a/nixos/modules/config/ldap.nix b/nixos/modules/config/ldap.nix
index 1a01533c585b..c87996df8855 100644
--- a/nixos/modules/config/ldap.nix
+++ b/nixos/modules/config/ldap.nix
@@ -108,7 +108,7 @@ in
 
         extraConfig = mkOption {
           default =  "";
-          type = types.string;
+          type = types.lines;
           description = ''
             Extra configuration options that will be added verbatim at
             the end of the nslcd configuration file (nslcd.conf).
@@ -120,7 +120,7 @@ in
         distinguishedName = mkOption {
           default = "";
           example = "cn=admin,dc=example,dc=com";
-          type = types.string;
+          type = types.str;
           description = ''
             The distinguished name to bind to the LDAP server with. If this
             is not specified, an anonymous bind will be done.
@@ -129,7 +129,7 @@ in
 
         password = mkOption {
           default = "/etc/ldap/bind.password";
-          type = types.string;
+          type = types.str;
           description = ''
             The path to a file containing the credentials to use when binding
             to the LDAP server (if not binding anonymously).
@@ -149,7 +149,7 @@ in
 
         policy = mkOption {
           default = "hard_open";
-          type = types.string;
+          type = types.enum [ "hard_open" "hard_init" "soft" ];
           description = ''
             Specifies the policy to use for reconnecting to an unavailable
             LDAP server. The default is <literal>hard_open</literal>, which
@@ -168,7 +168,7 @@ in
 
       extraConfig = mkOption {
         default = "";
-        type = types.string;
+        type = types.lines;
         description = ''
           Extra configuration options that will be added verbatim at
           the end of the ldap configuration file (ldap.conf).
diff --git a/nixos/modules/config/shells-environment.nix b/nixos/modules/config/shells-environment.nix
index bff0b2991323..533280890a70 100644
--- a/nixos/modules/config/shells-environment.nix
+++ b/nixos/modules/config/shells-environment.nix
@@ -41,20 +41,7 @@ in
         strings.  The latter is concatenated, interspersed with colon
         characters.
       '';
-      type = types.attrsOf (mkOptionType {
-        name = "a string or a list of strings";
-        merge = loc: defs:
-          let
-            defs' = filterOverrides defs;
-            res = (head defs').value;
-          in
-          if isList res then concatLists (getValues defs')
-          else if lessThan 1 (length defs') then
-            throw "The option `${showOption loc}' is defined multiple times, in ${showFiles (getFiles defs)}."
-          else if !isString res then
-            throw "The option `${showOption loc}' does not have a string value, in ${showFiles (getFiles defs)}."
-          else res;
-      });
+      type = types.attrsOf (types.loeOf types.str);
       apply = mapAttrs (n: v: if isList v then concatStringsSep ":" v else v);
     };
 
diff --git a/nixos/modules/config/system-environment.nix b/nixos/modules/config/system-environment.nix
index 3ab32f00fd1d..3362400326d2 100644
--- a/nixos/modules/config/system-environment.nix
+++ b/nixos/modules/config/system-environment.nix
@@ -23,20 +23,7 @@ in
         strings.  The latter is concatenated, interspersed with colon
         characters.
       '';
-      type = types.attrsOf (mkOptionType {
-        name = "a string or a list of strings";
-        merge = loc: defs:
-          let
-            defs' = filterOverrides defs;
-            res = (head defs').value;
-          in
-          if isList res then concatLists (getValues defs')
-          else if lessThan 1 (length defs') then
-            throw "The option `${showOption loc}' is defined multiple times, in ${showFiles (getFiles defs)}."
-          else if !isString res then
-            throw "The option `${showOption loc}' does not have a string value, in ${showFiles (getFiles defs)}."
-          else res;
-      });
+      type = types.attrsOf (types.loeOf types.str);
       apply = mapAttrs (n: v: if isList v then concatStringsSep ":" v else v);
     };
 
diff --git a/nixos/modules/programs/venus.nix b/nixos/modules/programs/venus.nix
index 3b5ae07e82f7..ca3188b18199 100644
--- a/nixos/modules/programs/venus.nix
+++ b/nixos/modules/programs/venus.nix
@@ -41,7 +41,7 @@ in
 
       dates = mkOption {
         default = "*:0/15";
-        type = types.string;
+        type = types.str;
         description = ''
           Specification (in the format described by
           <citerefentry><refentrytitle>systemd.time</refentrytitle>
@@ -52,7 +52,7 @@ in
 
       user = mkOption {
         default = "root";
-        type = types.string;
+        type = types.str;
         description = ''
           User for running venus script.
         '';
@@ -60,7 +60,7 @@ in
 
       group = mkOption {
         default = "root";
-        type = types.string;
+        type = types.str;
         description = ''
           Group for running venus script.
         '';
@@ -68,7 +68,7 @@ in
 
       name = mkOption {
         default = "NixOS Planet";
-        type = types.string;
+        type = types.str;
         description = ''
           Your planet's name.
         '';
@@ -76,7 +76,7 @@ in
 
       link = mkOption {
         default = "http://planet.nixos.org";
-        type = types.string;
+        type = types.str;
         description = ''
           Link to the main page.
         '';
@@ -84,7 +84,7 @@ in
 
       ownerName = mkOption {
         default = "Rok Garbas";
-        type = types.string;
+        type = types.str;
         description = ''
           Your name.
         '';
@@ -92,7 +92,7 @@ in
 
       ownerEmail = mkOption {
         default = "some@example.com";
-        type = types.string;
+        type = types.str;
         description = ''
           Your e-mail address.
         '';
diff --git a/nixos/modules/programs/wvdial.nix b/nixos/modules/programs/wvdial.nix
index 8e7d0e51a4e0..1ed929ed4afa 100644
--- a/nixos/modules/programs/wvdial.nix
+++ b/nixos/modules/programs/wvdial.nix
@@ -24,7 +24,7 @@ in
 
       dialerDefaults = mkOption {
         default = "";
-        type = types.string;
+        type = types.str;
         example = ''Init1 = AT+CGDCONT=1,"IP","internet.t-mobile"'';
         description = ''
           Contents of the "Dialer Defaults" section of
@@ -40,7 +40,7 @@ in
           persist
           noauth
         '';
-        type = types.string;
+        type = types.str;
         description = "Default ppp settings for wvdial.";
       };
 
diff --git a/nixos/modules/programs/xfs_quota.nix b/nixos/modules/programs/xfs_quota.nix
index d30a85922cff..90b6304fa999 100644
--- a/nixos/modules/programs/xfs_quota.nix
+++ b/nixos/modules/programs/xfs_quota.nix
@@ -32,25 +32,25 @@ in
             };
 
             fileSystem = mkOption {
-              type = types.string;
+              type = types.str;
               description = "XFS filesystem hosting the xfs_quota project.";
               default = "/";
             };
 
             path = mkOption {
-              type = types.string;
+              type = types.str;
               description = "Project directory.";
             };
 
             sizeSoftLimit = mkOption {
-              type = types.nullOr types.string;
+              type = types.nullOr types.str;
               default = null;
               example = "30g";
               description = "Soft limit of the project size";
             };
 
             sizeHardLimit = mkOption {
-              type = types.nullOr types.string;
+              type = types.nullOr types.str;
               default = null;
               example = "50g";
               description = "Hard limit of the project size.";
diff --git a/nixos/modules/security/pam.nix b/nixos/modules/security/pam.nix
index 474b93b4984d..88760574cbc6 100644
--- a/nixos/modules/security/pam.nix
+++ b/nixos/modules/security/pam.nix
@@ -419,7 +419,7 @@ in
     users.motd = mkOption {
       default = null;
       example = "Today is Sweetmorn, the 4th day of The Aftermath in the YOLD 3178.";
-      type = types.nullOr types.string;
+      type = types.nullOr types.lines;
       description = "Message of the day shown to users when they log in.";
     };
 
diff --git a/nixos/modules/security/prey.nix b/nixos/modules/security/prey.nix
index d7d438103a2c..1c643f2e1a57 100644
--- a/nixos/modules/security/prey.nix
+++ b/nixos/modules/security/prey.nix
@@ -24,7 +24,7 @@ in {
       };
 
       deviceKey = mkOption {
-        type = types.string;
+        type = types.str;
         description = ''
           <literal>Device key</literal> obtained by visiting
           <link xlink:href="https://panel.preyproject.com/devices" />
@@ -33,7 +33,7 @@ in {
       };
 
       apiKey = mkOption {
-        type = types.string;
+        type = types.str;
         description = ''
           <literal>API key</literal> obtained from
           <link xlink:href="https://panel.preyproject.com/profile" />.
diff --git a/nixos/modules/services/monitoring/smartd.nix b/nixos/modules/services/monitoring/smartd.nix
index 61ba16123252..1017005226b2 100644
--- a/nixos/modules/services/monitoring/smartd.nix
+++ b/nixos/modules/services/monitoring/smartd.nix
@@ -119,7 +119,7 @@ in
 
           recipient = mkOption {
             default = "root";
-            type = types.string;
+            type = types.str;
             description = "Recipient of the notification messages.";
           };
 
@@ -153,7 +153,7 @@ in
 
           display = mkOption {
             default = ":${toString config.services.xserver.display}";
-            type = types.string;
+            type = types.str;
             description = "DISPLAY to send X11 notifications to.";
           };
         };
diff --git a/nixos/modules/system/boot/loader/efi.nix b/nixos/modules/system/boot/loader/efi.nix
index 241cfc7e836d..726634e664d7 100644
--- a/nixos/modules/system/boot/loader/efi.nix
+++ b/nixos/modules/system/boot/loader/efi.nix
@@ -15,7 +15,7 @@ with lib;
     efiSysMountPoint = mkOption {
       default = "/boot";
 
-      type = types.string;
+      type = types.str;
 
       description = "Where the EFI System Partition is mounted.";
     };
diff --git a/nixos/modules/system/boot/luksroot.nix b/nixos/modules/system/boot/luksroot.nix
index 1b4f0d401e6d..4a14ff1879c9 100644
--- a/nixos/modules/system/boot/luksroot.nix
+++ b/nixos/modules/system/boot/luksroot.nix
@@ -242,20 +242,20 @@ in
 
         name = mkOption {
           example = "luksroot";
-          type = types.string;
+          type = types.str;
           description = "Named to be used for the generated device in /dev/mapper.";
         };
 
         device = mkOption {
           example = "/dev/sda2";
-          type = types.string;
+          type = types.str;
           description = "Path of the underlying block device.";
         };
 
         header = mkOption {
           default = null;
           example = "/root/header.img";
-          type = types.nullOr types.string;
+          type = types.nullOr types.str;
           description = ''
             The name of the file or block device that
             should be used as header for the encrypted device.
@@ -265,7 +265,7 @@ in
         keyFile = mkOption {
           default = null;
           example = "/dev/sdb1";
-          type = types.nullOr types.string;
+          type = types.nullOr types.str;
           description = ''
             The name of the file (can be a raw device or a partition) that
             should be used as the decryption key for the encrypted device. If
@@ -349,7 +349,7 @@ in
 
             ramfsMountPoint = mkOption {
               default = "/crypt-ramfs";
-              type = types.string;
+              type = types.str;
               description = "Path where the ramfs used to update the LUKS key will be mounted during early boot.";
             };
 
@@ -369,19 +369,19 @@ in
 
               fsType = mkOption {
                 default = "vfat";
-                type = types.string;
+                type = types.str;
                 description = "The filesystem of the unencrypted device.";
               };
 
               mountPoint = mkOption {
                 default = "/crypt-storage";
-                type = types.string;
+                type = types.str;
                 description = "Path where the unencrypted device will be mounted during early boot.";
               };
 
               path = mkOption {
                 default = "/crypt-storage/default";
-                type = types.string;
+                type = types.str;
                 description = ''
                   Absolute path of the salt on the unencrypted device with
                   that device's root directory as "/".
diff --git a/nixos/modules/tasks/encrypted-devices.nix b/nixos/modules/tasks/encrypted-devices.nix
index 0370e36fbec2..8b5dd22fd380 100644
--- a/nixos/modules/tasks/encrypted-devices.nix
+++ b/nixos/modules/tasks/encrypted-devices.nix
@@ -22,21 +22,21 @@ let
       blkDev = mkOption {
         default = null;
         example = "/dev/sda1";
-        type = types.uniq (types.nullOr types.string);
+        type = types.nullOr types.str;
         description = "Location of the backing encrypted device.";
       };
 
       label = mkOption {
         default = null;
         example = "rootfs";
-        type = types.uniq (types.nullOr types.string);
+        type = types.nullOr types.str;
         description = "Label of the backing encrypted device.";
       };
 
       keyFile = mkOption {
         default = null;
         example = "/root/.swapkey";
-        type = types.uniq (types.nullOr types.string);
+        type = types.nullOr types.str;
         description = "File system location of keyfile.";
       };
     };
diff --git a/nixos/modules/tasks/filesystems.nix b/nixos/modules/tasks/filesystems.nix
index ce21d9fe7621..ce9e3555b6cd 100644
--- a/nixos/modules/tasks/filesystems.nix
+++ b/nixos/modules/tasks/filesystems.nix
@@ -22,14 +22,14 @@ let
       device = mkOption {
         default = null;
         example = "/dev/sda";
-        type = types.uniq (types.nullOr types.string);
+        type = types.nullOr types.str;
         description = "Location of the device.";
       };
 
       label = mkOption {
         default = null;
         example = "root-partition";
-        type = types.uniq (types.nullOr types.string);
+        type = types.nullOr types.str;
         description = "Label of the device (if any).";
       };
 
diff --git a/nixos/modules/tasks/network-interfaces.nix b/nixos/modules/tasks/network-interfaces.nix
index a967fc77e686..9931c977e8f0 100644
--- a/nixos/modules/tasks/network-interfaces.nix
+++ b/nixos/modules/tasks/network-interfaces.nix
@@ -499,7 +499,7 @@ in
 
         interface = mkOption {
           example = "enp4s0";
-          type = types.string;
+          type = types.str;
           description = "The interface the macvlan will transmit packets through.";
         };
 
@@ -605,7 +605,7 @@ in
 
         interface = mkOption {
           example = "enp4s0";
-          type = types.string;
+          type = types.str;
           description = "The interface the vlan will transmit packets through.";
         };
 
diff --git a/nixos/modules/virtualisation/containers.nix b/nixos/modules/virtualisation/containers.nix
index 8d12c5a57fd9..02cf1fe46a55 100644
--- a/nixos/modules/virtualisation/containers.nix
+++ b/nixos/modules/virtualisation/containers.nix
@@ -108,7 +108,7 @@ in
             };
 
             hostAddress = mkOption {
-              type = types.nullOr types.string;
+              type = types.nullOr types.str;
               default = null;
               example = "10.231.136.1";
               description = ''
@@ -117,7 +117,7 @@ in
             };
 
             localAddress = mkOption {
-              type = types.nullOr types.string;
+              type = types.nullOr types.str;
               default = null;
               example = "10.231.136.2";
               description = ''
diff --git a/nixos/modules/virtualisation/docker.nix b/nixos/modules/virtualisation/docker.nix
index ba078cc0a11f..0115b972e80d 100644
--- a/nixos/modules/virtualisation/docker.nix
+++ b/nixos/modules/virtualisation/docker.nix
@@ -67,7 +67,7 @@ in
 
     postStart =
       mkOption {
-        type = types.string;
+        type = types.lines;
         default = ''
           while ! [ -e /var/run/docker.sock ]; do
             sleep 0.1