diff --git a/src/PseudoTypes/CallableString.php b/src/PseudoTypes/CallableString.php
new file mode 100644
index 0000000..e9c7c14
--- /dev/null
+++ b/src/PseudoTypes/CallableString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class CallableString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'callable-string';
+    }
+}
diff --git a/src/PseudoTypes/HtmlEscapedString.php b/src/PseudoTypes/HtmlEscapedString.php
new file mode 100644
index 0000000..7343517
--- /dev/null
+++ b/src/PseudoTypes/HtmlEscapedString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class HtmlEscapedString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'html-escaped-string';
+    }
+}
diff --git a/src/PseudoTypes/LowercaseString.php b/src/PseudoTypes/LowercaseString.php
new file mode 100644
index 0000000..8fddbaa
--- /dev/null
+++ b/src/PseudoTypes/LowercaseString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class LowercaseString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'lowercase-string';
+    }
+}
diff --git a/src/PseudoTypes/NonEmptyLowercaseString.php b/src/PseudoTypes/NonEmptyLowercaseString.php
new file mode 100644
index 0000000..bf24aaa
--- /dev/null
+++ b/src/PseudoTypes/NonEmptyLowercaseString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class NonEmptyLowercaseString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'non-empty-lowercase-string';
+    }
+}
diff --git a/src/PseudoTypes/NonEmptyString.php b/src/PseudoTypes/NonEmptyString.php
new file mode 100644
index 0000000..f67c239
--- /dev/null
+++ b/src/PseudoTypes/NonEmptyString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class NonEmptyString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'non-empty-string';
+    }
+}
diff --git a/src/PseudoTypes/NumericString.php b/src/PseudoTypes/NumericString.php
new file mode 100644
index 0000000..64300f6
--- /dev/null
+++ b/src/PseudoTypes/NumericString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class NumericString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'numeric-string';
+    }
+}
diff --git a/src/PseudoTypes/PositiveInteger.php b/src/PseudoTypes/PositiveInteger.php
new file mode 100644
index 0000000..88ac7ed
--- /dev/null
+++ b/src/PseudoTypes/PositiveInteger.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\Integer;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class PositiveInteger extends Integer implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new Integer();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'positive-int';
+    }
+}
diff --git a/src/PseudoTypes/TraitString.php b/src/PseudoTypes/TraitString.php
new file mode 100644
index 0000000..4e2f5df
--- /dev/null
+++ b/src/PseudoTypes/TraitString.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\PseudoTypes;
+
+use phpDocumentor\Reflection\PseudoType;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\String_;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class TraitString extends String_ implements PseudoType
+{
+    public function underlyingType() : Type
+    {
+        return new String_();
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        return 'trait-string';
+    }
+}
diff --git a/src/TypeResolver.php b/src/TypeResolver.php
index 07e1b83..eed56e6 100644
--- a/src/TypeResolver.php
+++ b/src/TypeResolver.php
@@ -22,6 +22,7 @@
 use phpDocumentor\Reflection\Types\Context;
 use phpDocumentor\Reflection\Types\Expression;
 use phpDocumentor\Reflection\Types\Integer;
+use phpDocumentor\Reflection\Types\InterfaceString;
 use phpDocumentor\Reflection\Types\Intersection;
 use phpDocumentor\Reflection\Types\Iterable_;
 use phpDocumentor\Reflection\Types\Nullable;
@@ -71,29 +72,39 @@ final class TypeResolver
     private $keywords = [
         'string' => Types\String_::class,
         'class-string' => Types\ClassString::class,
+        'interface-string' => Types\InterfaceString::class,
+        'html-escaped-string' => PseudoTypes\HtmlEscapedString::class,
+        'lowercase-string' => PseudoTypes\LowercaseString::class,
+        'non-empty-lowercase-string' => PseudoTypes\NonEmptyLowercaseString::class,
+        'non-empty-string' => PseudoTypes\NonEmptyString::class,
+        'numeric-string' => PseudoTypes\NumericString::class,
+        'trait-string' => PseudoTypes\TraitString::class,
         'int' => Types\Integer::class,
         'integer' => Types\Integer::class,
+        'positive-int' => PseudoTypes\PositiveInteger::class,
         'bool' => Types\Boolean::class,
         'boolean' => Types\Boolean::class,
         'real' => Types\Float_::class,
         'float' => Types\Float_::class,
         'double' => Types\Float_::class,
-        'object' => Object_::class,
+        'object' => Types\Object_::class,
         'mixed' => Types\Mixed_::class,
-        'array' => Array_::class,
+        'array' => Types\Array_::class,
+        'array-key' => Types\ArrayKey::class,
         'resource' => Types\Resource_::class,
         'void' => Types\Void_::class,
         'null' => Types\Null_::class,
         'scalar' => Types\Scalar::class,
         'callback' => Types\Callable_::class,
         'callable' => Types\Callable_::class,
+        'callable-string' => PseudoTypes\CallableString::class,
         'false' => PseudoTypes\False_::class,
         'true' => PseudoTypes\True_::class,
         'self' => Types\Self_::class,
         '$this' => Types\This::class,
         'static' => Types\Static_::class,
         'parent' => Types\Parent_::class,
-        'iterable' => Iterable_::class,
+        'iterable' => Types\Iterable_::class,
     ];
 
     /**
@@ -237,6 +248,8 @@ private function parseTypes(ArrayIterator $tokens, Context $context, int $parser
                 if ($classType !== null) {
                     if ((string) $classType === 'class-string') {
                         $types[] = $this->resolveClassString($tokens, $context);
+                    } elseif ((string) $classType === 'interface-string') {
+                        $types[] = $this->resolveInterfaceString($tokens, $context);
                     } else {
                         $types[] = $this->resolveCollection($tokens, $classType, $context);
                     }
@@ -446,6 +459,39 @@ private function resolveClassString(ArrayIterator $tokens, Context $context) : T
         return new ClassString($classType->getFqsen());
     }
 
+    /**
+     * Resolves class string
+     *
+     * @param ArrayIterator<int, (string|null)> $tokens
+     */
+    private function resolveInterfaceString(ArrayIterator $tokens, Context $context) : Type
+    {
+        $tokens->next();
+
+        $classType = $this->parseTypes($tokens, $context, self::PARSER_IN_COLLECTION_EXPRESSION);
+
+        if (!$classType instanceof Object_ || $classType->getFqsen() === null) {
+            throw new RuntimeException(
+                $classType . ' is not a interface string'
+            );
+        }
+
+        $token = $tokens->current();
+        if ($token !== '>') {
+            if (empty($token)) {
+                throw new RuntimeException(
+                    'interface-string: ">" is missing'
+                );
+            }
+
+            throw new RuntimeException(
+                'Unexpected character "' . $token . '", ">" is missing'
+            );
+        }
+
+        return new InterfaceString($classType->getFqsen());
+    }
+
     /**
      * Resolves the collection values and keys
      *
diff --git a/src/Types/ArrayKey.php b/src/Types/ArrayKey.php
new file mode 100644
index 0000000..df21a45
--- /dev/null
+++ b/src/Types/ArrayKey.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\Types;
+
+/**
+ * Value Object representing a array-key Type.
+ *
+ * A array-key Type is the supertype (but not a union) of int and string.
+ *
+ * @psalm-immutable
+ */
+final class ArrayKey extends AggregatedType
+{
+    public function __construct()
+    {
+        parent::__construct([new String_(), new Integer()], '|');
+    }
+
+    public function __toString() : string
+    {
+        return 'array-key';
+    }
+}
diff --git a/src/Types/Integer.php b/src/Types/Integer.php
index 2cfd7e9..858d4ab 100644
--- a/src/Types/Integer.php
+++ b/src/Types/Integer.php
@@ -20,7 +20,7 @@
  *
  * @psalm-immutable
  */
-final class Integer implements Type
+class Integer implements Type
 {
     /**
      * Returns a rendered output of the Type as it would be used in a DocBlock.
diff --git a/src/Types/InterfaceString.php b/src/Types/InterfaceString.php
new file mode 100644
index 0000000..8400bef
--- /dev/null
+++ b/src/Types/InterfaceString.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\Types;
+
+use phpDocumentor\Reflection\Fqsen;
+use phpDocumentor\Reflection\Type;
+
+/**
+ * Value Object representing the type 'string'.
+ *
+ * @psalm-immutable
+ */
+final class InterfaceString implements Type
+{
+    /** @var Fqsen|null */
+    private $fqsen;
+
+    /**
+     * Initializes this representation of a class string with the given Fqsen.
+     */
+    public function __construct(?Fqsen $fqsen = null)
+    {
+        $this->fqsen = $fqsen;
+    }
+
+    /**
+     * Returns the FQSEN associated with this object.
+     */
+    public function getFqsen() : ?Fqsen
+    {
+        return $this->fqsen;
+    }
+
+    /**
+     * Returns a rendered output of the Type as it would be used in a DocBlock.
+     */
+    public function __toString() : string
+    {
+        if ($this->fqsen === null) {
+            return 'interface-string';
+        }
+
+        return 'interface-string<' . (string) $this->fqsen . '>';
+    }
+}
diff --git a/src/Types/String_.php b/src/Types/String_.php
index 6b92e41..010682a 100644
--- a/src/Types/String_.php
+++ b/src/Types/String_.php
@@ -20,7 +20,7 @@
  *
  * @psalm-immutable
  */
-final class String_ implements Type
+class String_ implements Type
 {
     /**
      * Returns a rendered output of the Type as it would be used in a DocBlock.
diff --git a/tests/unit/TypeResolverTest.php b/tests/unit/TypeResolverTest.php
index 92c1bc5..aa191b7 100644
--- a/tests/unit/TypeResolverTest.php
+++ b/tests/unit/TypeResolverTest.php
@@ -20,6 +20,7 @@
 use phpDocumentor\Reflection\Types\Context;
 use phpDocumentor\Reflection\Types\Expression;
 use phpDocumentor\Reflection\Types\Integer;
+use phpDocumentor\Reflection\Types\InterfaceString;
 use phpDocumentor\Reflection\Types\Intersection;
 use phpDocumentor\Reflection\Types\Iterable_;
 use phpDocumentor\Reflection\Types\Null_;
@@ -79,6 +80,30 @@ public function testResolvingClassStrings(string $classString, bool $throwsExcep
         $this->assertInstanceOf(ClassString::class, $resolvedType);
     }
 
+    /**
+     * @uses         \phpDocumentor\Reflection\Types\Context
+     * @uses         \phpDocumentor\Reflection\Types\Object_
+     * @uses         \phpDocumentor\Reflection\Types\String_
+     *
+     * @covers ::__construct
+     * @covers ::resolve
+     * @covers ::<private>
+     *
+     * @dataProvider provideInterfaceStrings
+     */
+    public function testResolvingInterfaceStrings(string $interfaceString, bool $throwsException) : void
+    {
+        $fixture = new TypeResolver();
+
+        if ($throwsException) {
+            $this->expectException('RuntimeException');
+        }
+
+        $resolvedType = $fixture->resolve($interfaceString, new Context(''));
+
+        $this->assertInstanceOf(InterfaceString::class, $resolvedType);
+    }
+
     /**
      * @uses         \phpDocumentor\Reflection\Types\Context
      * @uses         \phpDocumentor\Reflection\Types\Object_
@@ -698,8 +723,15 @@ public function provideKeywords() : array
         return [
             ['string', Types\String_::class],
             ['class-string', Types\ClassString::class],
+            ['html-escaped-string', PseudoTypes\HtmlEscapedString::class],
+            ['lowercase-string', PseudoTypes\LowercaseString::class],
+            ['non-empty-lowercase-string', PseudoTypes\NonEmptyLowercaseString::class],
+            ['non-empty-string', PseudoTypes\NonEmptyString::class],
+            ['numeric-string', PseudoTypes\NumericString::class],
+            ['trait-string', PseudoTypes\TraitString::class],
             ['int', Types\Integer::class],
             ['integer', Types\Integer::class],
+            ['positive-int', PseudoTypes\PositiveInteger::class],
             ['float', Types\Float_::class],
             ['double', Types\Float_::class],
             ['bool', Types\Boolean::class],
@@ -711,17 +743,19 @@ public function provideKeywords() : array
             ['resource', Types\Resource_::class],
             ['null', Types\Null_::class],
             ['callable', Types\Callable_::class],
+            ['callable-string', PseudoTypes\CallableString::class],
             ['callback', Types\Callable_::class],
-            ['array', Array_::class],
+            ['array', Types\Array_::class],
+            ['array-key', Types\ArrayKey::class],
             ['scalar', Types\Scalar::class],
-            ['object', Object_::class],
+            ['object', Types\Object_::class],
             ['mixed', Types\Mixed_::class],
             ['void', Types\Void_::class],
             ['$this', Types\This::class],
             ['static', Types\Static_::class],
             ['self', Types\Self_::class],
             ['parent', Types\Parent_::class],
-            ['iterable', Iterable_::class],
+            ['iterable', Types\Iterable_::class],
         ];
     }
 
@@ -739,6 +773,20 @@ public function provideClassStrings() : array
         ];
     }
 
+    /**
+     * Returns a list of interface string types and whether they throw an exception.
+     *
+     * @return (string|bool)[][]
+     */
+    public function provideInterfaceStrings() : array
+    {
+        return [
+            ['interface-string<\phpDocumentor\Reflection>', false],
+            ['interface-string<\phpDocumentor\Reflection\DocBlock>', false],
+            ['interface-string<string>', true],
+        ];
+    }
+
     /**
      * Provides a list of FQSENs to test the resolution patterns with.
      *
diff --git a/tests/unit/Types/ArrayKeyTest.php b/tests/unit/Types/ArrayKeyTest.php
new file mode 100644
index 0000000..86bbe70
--- /dev/null
+++ b/tests/unit/Types/ArrayKeyTest.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\Types;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @coversDefaultClass \phpDocumentor\Reflection\Types\ArrayKey
+ */
+final class ArrayKeyTest extends TestCase
+{
+    /**
+     * @covers ::__construct
+     * @covers ::__toString
+     */
+    public function testArrayKeyCanBeConstructedAndStringifiedCorrectly() : void
+    {
+        $this->assertSame('array-key', (string) (new ArrayKey()));
+    }
+
+    /**
+     * @uses ::__construct
+     *
+     * @covers ::getIterator
+     */
+    public function testArrayKeyCanBeIterated() : void
+    {
+        $types = [String_::class, Integer::class];
+
+        foreach (new ArrayKey() as $index => $type) {
+            $this->assertInstanceOf($types[$index], $type);
+        }
+    }
+}
diff --git a/tests/unit/Types/ClassStringTest.php b/tests/unit/Types/ClassStringTest.php
index 4f779d4..37c9173 100644
--- a/tests/unit/Types/ClassStringTest.php
+++ b/tests/unit/Types/ClassStringTest.php
@@ -36,7 +36,7 @@ public function testClassStringStringifyCorrectly(ClassString $array, string $ex
     public function provideClassStrings() : array
     {
         return [
-            'generic clss string' => [new ClassString(), 'class-string'],
+            'generic class string' => [new ClassString(), 'class-string'],
             'typed class string' => [new ClassString(new Fqsen('\Foo\Bar')), 'class-string<\Foo\Bar>'],
         ];
     }
diff --git a/tests/unit/Types/InterfaceStringTest.php b/tests/unit/Types/InterfaceStringTest.php
new file mode 100644
index 0000000..f4afc8a
--- /dev/null
+++ b/tests/unit/Types/InterfaceStringTest.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link      http://phpdoc.org
+ */
+
+namespace phpDocumentor\Reflection\Types;
+
+use phpDocumentor\Reflection\Fqsen;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @coversDefaultClass \phpDocumentor\Reflection\Types\InterfaceString
+ */
+class InterfaceStringTest extends TestCase
+{
+    /**
+     * @dataProvider provideInterfaceStrings
+     * @covers ::__toString
+     */
+    public function testInterfaceStringStringifyCorrectly(InterfaceString $array, string $expectedString) : void
+    {
+        $this->assertSame($expectedString, (string) $array);
+    }
+
+    /**
+     * @return mixed[]
+     */
+    public function provideInterfaceStrings() : array
+    {
+        return [
+            'generic interface string' => [new InterfaceString(), 'interface-string'],
+            'typed interface string' => [new InterfaceString(new Fqsen('\Foo\Bar')), 'interface-string<\Foo\Bar>'],
+        ];
+    }
+}