diff --git a/src/Types/ArrayKey.php b/src/PseudoTypes/ArrayKey.php
similarity index 72%
rename from src/Types/ArrayKey.php
rename to src/PseudoTypes/ArrayKey.php
index fc3641ed..ce3dd805 100644
--- a/src/Types/ArrayKey.php
+++ b/src/PseudoTypes/ArrayKey.php
@@ -11,15 +11,17 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
 use phpDocumentor\Reflection\PseudoType;
 use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\AggregatedType;
+use phpDocumentor\Reflection\Types\Compound;
+use phpDocumentor\Reflection\Types\Integer;
+use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing a array-key Type.
- *
- * A array-key Type is the supertype (but not a union) of int and string.
+ * Value Object representing the type `array-key`.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/ArrayShape.php b/src/PseudoTypes/ArrayShape.php
index e0d0c736..45b7767c 100644
--- a/src/PseudoTypes/ArrayShape.php
+++ b/src/PseudoTypes/ArrayShape.php
@@ -16,7 +16,6 @@
 use phpDocumentor\Reflection\PseudoType;
 use phpDocumentor\Reflection\Type;
 use phpDocumentor\Reflection\Types\Array_;
-use phpDocumentor\Reflection\Types\ArrayKey;
 use phpDocumentor\Reflection\Types\Mixed_;
 
 use function implode;
diff --git a/src/PseudoTypes/CallableString.php b/src/PseudoTypes/CallableString.php
index b6934561..ff50497a 100644
--- a/src/PseudoTypes/CallableString.php
+++ b/src/PseudoTypes/CallableString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'callable-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/Types/ClassString.php b/src/PseudoTypes/ClassString.php
similarity index 89%
rename from src/Types/ClassString.php
rename to src/PseudoTypes/ClassString.php
index fbdd879b..02ee2b8e 100644
--- a/src/Types/ClassString.php
+++ b/src/PseudoTypes/ClassString.php
@@ -11,14 +11,15 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
 use phpDocumentor\Reflection\Fqsen;
 use phpDocumentor\Reflection\PseudoType;
 use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'class-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/HtmlEscapedString.php b/src/PseudoTypes/HtmlEscapedString.php
index aa4d8db5..295c2758 100644
--- a/src/PseudoTypes/HtmlEscapedString.php
+++ b/src/PseudoTypes/HtmlEscapedString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'html-escaped-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/Types/InterfaceString.php b/src/PseudoTypes/InterfaceString.php
similarity index 75%
rename from src/Types/InterfaceString.php
rename to src/PseudoTypes/InterfaceString.php
index 9836961f..89248144 100644
--- a/src/Types/InterfaceString.php
+++ b/src/PseudoTypes/InterfaceString.php
@@ -11,17 +11,19 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
 use phpDocumentor\Reflection\Fqsen;
+use phpDocumentor\Reflection\PseudoType;
 use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type `interface-string`.
  *
  * @psalm-immutable
  */
-final class InterfaceString implements Type
+final class InterfaceString extends String_ implements PseudoType
 {
     /** @var Fqsen|null */
     private $fqsen;
@@ -34,6 +36,11 @@ public function __construct(?Fqsen $fqsen = null)
         $this->fqsen = $fqsen;
     }
 
+    public function underlyingType(): Type
+    {
+        return new String_();
+    }
+
     /**
      * Returns the FQSEN associated with this object.
      */
diff --git a/src/PseudoTypes/KeyOf.php b/src/PseudoTypes/KeyOf.php
index 6cf5e0a7..0f26b098 100644
--- a/src/PseudoTypes/KeyOf.php
+++ b/src/PseudoTypes/KeyOf.php
@@ -15,7 +15,6 @@
 
 use phpDocumentor\Reflection\PseudoType;
 use phpDocumentor\Reflection\Type;
-use phpDocumentor\Reflection\Types\ArrayKey;
 
 /**
  * Value Object representing the `key-of` type.
diff --git a/src/PseudoTypes/LiteralString.php b/src/PseudoTypes/LiteralString.php
index 690f782b..a38518bf 100644
--- a/src/PseudoTypes/LiteralString.php
+++ b/src/PseudoTypes/LiteralString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'literal-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/LowercaseString.php b/src/PseudoTypes/LowercaseString.php
index 6325492a..f73d100f 100644
--- a/src/PseudoTypes/LowercaseString.php
+++ b/src/PseudoTypes/LowercaseString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'lowercase-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/NonEmptyLowercaseString.php b/src/PseudoTypes/NonEmptyLowercaseString.php
index 86400165..c2f2b496 100644
--- a/src/PseudoTypes/NonEmptyLowercaseString.php
+++ b/src/PseudoTypes/NonEmptyLowercaseString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'non-empty-lowercase-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/NonEmptyString.php b/src/PseudoTypes/NonEmptyString.php
index d72d127c..afa782a8 100644
--- a/src/PseudoTypes/NonEmptyString.php
+++ b/src/PseudoTypes/NonEmptyString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'non-empty-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/NumericString.php b/src/PseudoTypes/NumericString.php
index b62aa45a..f45ec1d0 100644
--- a/src/PseudoTypes/NumericString.php
+++ b/src/PseudoTypes/NumericString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type 'numeric-string'.
  *
  * @psalm-immutable
  */
diff --git a/src/PseudoTypes/TraitString.php b/src/PseudoTypes/TraitString.php
index ac217c25..409ad0b6 100644
--- a/src/PseudoTypes/TraitString.php
+++ b/src/PseudoTypes/TraitString.php
@@ -18,7 +18,7 @@
 use phpDocumentor\Reflection\Types\String_;
 
 /**
- * Value Object representing the type 'string'.
+ * Value Object representing the type `trait-string`.
  *
  * @psalm-immutable
  */
diff --git a/src/TypeResolver.php b/src/TypeResolver.php
index e2b8089b..66b47e83 100644
--- a/src/TypeResolver.php
+++ b/src/TypeResolver.php
@@ -15,9 +15,11 @@
 
 use Doctrine\Deprecations\Deprecation;
 use InvalidArgumentException;
+use phpDocumentor\Reflection\PseudoTypes\ArrayKey;
 use phpDocumentor\Reflection\PseudoTypes\ArrayShape;
 use phpDocumentor\Reflection\PseudoTypes\ArrayShapeItem;
 use phpDocumentor\Reflection\PseudoTypes\CallableString;
+use phpDocumentor\Reflection\PseudoTypes\ClassString;
 use phpDocumentor\Reflection\PseudoTypes\Conditional;
 use phpDocumentor\Reflection\PseudoTypes\ConditionalForParameter;
 use phpDocumentor\Reflection\PseudoTypes\ConstExpression;
@@ -28,6 +30,7 @@
 use phpDocumentor\Reflection\PseudoTypes\HtmlEscapedString;
 use phpDocumentor\Reflection\PseudoTypes\IntegerRange;
 use phpDocumentor\Reflection\PseudoTypes\IntegerValue;
+use phpDocumentor\Reflection\PseudoTypes\InterfaceString;
 use phpDocumentor\Reflection\PseudoTypes\IntMask;
 use phpDocumentor\Reflection\PseudoTypes\IntMaskOf;
 use phpDocumentor\Reflection\PseudoTypes\KeyOf;
@@ -53,17 +56,14 @@
 use phpDocumentor\Reflection\PseudoTypes\ValueOf;
 use phpDocumentor\Reflection\Types\AggregatedType;
 use phpDocumentor\Reflection\Types\Array_;
-use phpDocumentor\Reflection\Types\ArrayKey;
 use phpDocumentor\Reflection\Types\Boolean;
 use phpDocumentor\Reflection\Types\Callable_;
 use phpDocumentor\Reflection\Types\CallableParameter;
-use phpDocumentor\Reflection\Types\ClassString;
 use phpDocumentor\Reflection\Types\Compound;
 use phpDocumentor\Reflection\Types\Context;
 use phpDocumentor\Reflection\Types\Expression;
 use phpDocumentor\Reflection\Types\Float_;
 use phpDocumentor\Reflection\Types\Integer;
-use phpDocumentor\Reflection\Types\InterfaceString;
 use phpDocumentor\Reflection\Types\Intersection;
 use phpDocumentor\Reflection\Types\Iterable_;
 use phpDocumentor\Reflection\Types\Mixed_;
diff --git a/tests/unit/Types/ArrayKeyTest.php b/tests/unit/PseudoTypes/ArrayKeyTest.php
similarity index 75%
rename from tests/unit/Types/ArrayKeyTest.php
rename to tests/unit/PseudoTypes/ArrayKeyTest.php
index 88d511c1..8702f068 100644
--- a/tests/unit/Types/ArrayKeyTest.php
+++ b/tests/unit/PseudoTypes/ArrayKeyTest.php
@@ -11,12 +11,14 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
+use phpDocumentor\Reflection\Types\Integer;
+use phpDocumentor\Reflection\Types\String_;
 use PHPUnit\Framework\TestCase;
 
 /**
- * @coversDefaultClass \phpDocumentor\Reflection\Types\ArrayKey
+ * @coversDefaultClass \phpDocumentor\Reflection\PseudoTypes\ArrayKey
  */
 final class ArrayKeyTest extends TestCase
 {
@@ -30,7 +32,7 @@ public function testArrayKeyCanBeConstructedAndStringifiedCorrectly(): void
     }
 
     /**
-     * @uses \phpDocumentor\Reflection\Types\ArrayKey::__construct
+     * @uses \phpDocumentor\Reflection\PseudoTypes\ArrayKey::__construct
      *
      * @covers ::getIterator
      */
diff --git a/tests/unit/Types/ClassStringTest.php b/tests/unit/PseudoTypes/ClassStringTest.php
similarity index 88%
rename from tests/unit/Types/ClassStringTest.php
rename to tests/unit/PseudoTypes/ClassStringTest.php
index 8f77e762..b83ca5c4 100644
--- a/tests/unit/Types/ClassStringTest.php
+++ b/tests/unit/PseudoTypes/ClassStringTest.php
@@ -11,13 +11,13 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
 use phpDocumentor\Reflection\Fqsen;
 use PHPUnit\Framework\TestCase;
 
 /**
- * @coversDefaultClass \phpDocumentor\Reflection\Types\ClassString
+ * @coversDefaultClass \phpDocumentor\Reflection\PseudoTypes\ClassString
  */
 class ClassStringTest extends TestCase
 {
diff --git a/tests/unit/Types/InterfaceStringTest.php b/tests/unit/PseudoTypes/InterfaceStringTest.php
similarity index 88%
rename from tests/unit/Types/InterfaceStringTest.php
rename to tests/unit/PseudoTypes/InterfaceStringTest.php
index 19d20012..92e2ee21 100644
--- a/tests/unit/Types/InterfaceStringTest.php
+++ b/tests/unit/PseudoTypes/InterfaceStringTest.php
@@ -11,13 +11,13 @@
  * @link      http://phpdoc.org
  */
 
-namespace phpDocumentor\Reflection\Types;
+namespace phpDocumentor\Reflection\PseudoTypes;
 
 use phpDocumentor\Reflection\Fqsen;
 use PHPUnit\Framework\TestCase;
 
 /**
- * @coversDefaultClass \phpDocumentor\Reflection\Types\InterfaceString
+ * @coversDefaultClass \phpDocumentor\Reflection\PseudoTypes\InterfaceString
  */
 class InterfaceStringTest extends TestCase
 {
diff --git a/tests/unit/TypeResolverTest.php b/tests/unit/TypeResolverTest.php
index 4cff6369..b1bf9e26 100644
--- a/tests/unit/TypeResolverTest.php
+++ b/tests/unit/TypeResolverTest.php
@@ -15,9 +15,11 @@
 
 use Doctrine\Deprecations\PHPUnit\VerifyDeprecations;
 use InvalidArgumentException;
+use phpDocumentor\Reflection\PseudoTypes\ArrayKey;
 use phpDocumentor\Reflection\PseudoTypes\ArrayShape;
 use phpDocumentor\Reflection\PseudoTypes\ArrayShapeItem;
 use phpDocumentor\Reflection\PseudoTypes\CallableString;
+use phpDocumentor\Reflection\PseudoTypes\ClassString;
 use phpDocumentor\Reflection\PseudoTypes\Conditional;
 use phpDocumentor\Reflection\PseudoTypes\ConditionalForParameter;
 use phpDocumentor\Reflection\PseudoTypes\ConstExpression;
@@ -27,6 +29,7 @@
 use phpDocumentor\Reflection\PseudoTypes\HtmlEscapedString;
 use phpDocumentor\Reflection\PseudoTypes\IntegerRange;
 use phpDocumentor\Reflection\PseudoTypes\IntegerValue;
+use phpDocumentor\Reflection\PseudoTypes\InterfaceString;
 use phpDocumentor\Reflection\PseudoTypes\IntMask;
 use phpDocumentor\Reflection\PseudoTypes\IntMaskOf;
 use phpDocumentor\Reflection\PseudoTypes\KeyOf;
@@ -51,17 +54,14 @@
 use phpDocumentor\Reflection\PseudoTypes\True_;
 use phpDocumentor\Reflection\PseudoTypes\ValueOf;
 use phpDocumentor\Reflection\Types\Array_;
-use phpDocumentor\Reflection\Types\ArrayKey;
 use phpDocumentor\Reflection\Types\Boolean;
 use phpDocumentor\Reflection\Types\Callable_;
 use phpDocumentor\Reflection\Types\CallableParameter;
-use phpDocumentor\Reflection\Types\ClassString;
 use phpDocumentor\Reflection\Types\Compound;
 use phpDocumentor\Reflection\Types\Context;
 use phpDocumentor\Reflection\Types\Expression;
 use phpDocumentor\Reflection\Types\Float_;
 use phpDocumentor\Reflection\Types\Integer;
-use phpDocumentor\Reflection\Types\InterfaceString;
 use phpDocumentor\Reflection\Types\Intersection;
 use phpDocumentor\Reflection\Types\Iterable_;
 use phpDocumentor\Reflection\Types\Mixed_;