diff --git a/src/Constants.php b/src/Constants.php
index 99c99b2..9979c8b 100644
--- a/src/Constants.php
+++ b/src/Constants.php
@@ -27,32 +27,7 @@ class Constants
     public const NS_XSI = 'http://www.w3.org/2001/XMLSchema-instance';
 
     /**
-     * The namespace-attribute values for xs:any elements
+     * The maximum amount of child nodes this library is willing to handle.
      */
-    public const XS_ANY_NS_ANY = '##any';
-    public const XS_ANY_NS_LOCAL = '##local';
-    public const XS_ANY_NS_OTHER = '##other';
-    public const XS_ANY_NS_TARGET = '##targetNamespace';
-
-    public const XS_ANY_NS = [
-        self::XS_ANY_NS_ANY,
-        self::XS_ANY_NS_LOCAL,
-        self::XS_ANY_NS_OTHER,
-        self::XS_ANY_NS_TARGET,
-    ];
-
-    /**
-     * The processContents-attribute values for xs:any elements
-     */
-    public const XS_ANY_PROCESS_LAX = 'lax';
-    public const XS_ANY_PROCESS_SKIP = 'skip';
-    public const XS_ANY_PROCESS_STRICT = 'strict';
-
-    public const XS_ANY_PROCESS = [
-        self::XS_ANY_PROCESS_LAX,
-        self::XS_ANY_PROCESS_SKIP,
-        self::XS_ANY_PROCESS_STRICT,
-    ];
-
     public const UNBOUNDED_LIMIT = 10000;
 }
diff --git a/src/ExtendableAttributesTrait.php b/src/ExtendableAttributesTrait.php
index 98e8695..af5090a 100644
--- a/src/ExtendableAttributesTrait.php
+++ b/src/ExtendableAttributesTrait.php
@@ -9,6 +9,7 @@
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\Attribute;
 use SimpleSAML\XML\Constants as C;
+use SimpleSAML\XML\XsNamespace as NS;
 
 use function array_diff;
 use function array_map;
@@ -100,25 +101,25 @@ protected static function getAttributesNSFromXML(DOMElement $xml, string|array $
         // Validate namespace value
         if (!is_array($namespace)) {
             // Must be one of the predefined values
-            Assert::oneOf($namespace, C::XS_ANY_NS);
+            Assert::oneOf($namespace, NS::cases());
 
-            if ($namespace === C::XS_ANY_NS_ANY) {
+            if ($namespace === NS::ANY) {
                 foreach ($xml->attributes as $a) {
                     $attributes[] = new Attribute($a->namespaceURI, $a->prefix, $a->localName, $a->nodeValue);
                 }
-            } elseif ($namespace === C::XS_ANY_NS_LOCAL) {
+            } elseif ($namespace === NS::LOCAL) {
                 foreach ($xml->attributes as $a) {
                     if ($a->namespaceURI === null) {
                         $attributes[] = new Attribute($a->namespaceURI, $a->prefix, $a->localName, $a->nodeValue);
                     }
                 }
-            } elseif ($namespace === C::XS_ANY_NS_OTHER) {
+            } elseif ($namespace === NS::OTHER) {
                 foreach ($xml->attributes as $a) {
                     if (!in_array($a->namespaceURI, [static::NS, null], true)) {
                         $attributes[] = new Attribute($a->namespaceURI, $a->prefix, $a->localName, $a->nodeValue);
                     }
                 }
-            } elseif ($namespace === C::XS_ANY_NS_TARGET) {
+            } elseif ($namespace === NS::TARGET) {
                 foreach ($xml->attributes as $a) {
                     if ($a->namespaceURI === static::NS) {
                         $attributes[] = new Attribute($a->namespaceURI, $a->prefix, $a->localName, $a->nodeValue);
@@ -129,16 +130,16 @@ protected static function getAttributesNSFromXML(DOMElement $xml, string|array $
             // Array must be non-empty and cannot contain ##any or ##other
             Assert::notEmpty($namespace);
             Assert::allStringNotEmpty($namespace);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_ANY);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_OTHER);
+            Assert::allNotSame($namespace, NS::ANY);
+            Assert::allNotSame($namespace, NS::OTHER);
 
             // Replace the ##targetedNamespace with the actual namespace
-            if (($key = array_search(C::XS_ANY_NS_TARGET, $namespace)) !== false) {
+            if (($key = array_search(NS::TARGET, $namespace)) !== false) {
                 $namespace[$key] = static::NS;
             }
 
             // Replace the ##local with null
-            if (($key = array_search(C::XS_ANY_NS_LOCAL, $namespace)) !== false) {
+            if (($key = array_search(NS::LOCAL, $namespace)) !== false) {
                 $namespace[$key] = null;
             }
 
@@ -170,13 +171,12 @@ protected function setAttributesNS(array $attributes): void
         // Validate namespace value
         if (!is_array($namespace)) {
             // Must be one of the predefined values
-            Assert::oneOf($namespace, C::XS_ANY_NS);
+            Assert::oneOf($namespace, NS::cases());
         } else {
             // Array must be non-empty and cannot contain ##any or ##other
             Assert::notEmpty($namespace);
-            Assert::allStringNotEmpty($namespace);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_ANY);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_OTHER);
+            Assert::allNotSame($namespace, NS::ANY);
+            Assert::allNotSame($namespace, NS::OTHER);
         }
 
         // Get namespaces for all attributes
@@ -191,7 +191,7 @@ function (Attribute $attr) {
             $attributes,
         );
 
-        if ($namespace === C::XS_ANY_NS_LOCAL) {
+        if ($namespace === NS::LOCAL) {
             // If ##local then all namespaces must be null
             Assert::allNull($actual_namespaces);
         } elseif (is_array($namespace)) {
@@ -199,12 +199,12 @@ function (Attribute $attr) {
             $allowed_namespaces = $namespace;
 
             // Replace the ##targetedNamespace with the actual namespace
-            if (($key = array_search(C::XS_ANY_NS_TARGET, $allowed_namespaces)) !== false) {
+            if (($key = array_search(NS::TARGET, $allowed_namespaces)) !== false) {
                 $allowed_namespaces[$key] = static::NS;
             }
 
             // Replace the ##local with null
-            if (($key = array_search(C::XS_ANY_NS_LOCAL, $allowed_namespaces)) !== false) {
+            if (($key = array_search(NS::LOCAL, $allowed_namespaces)) !== false) {
                 $allowed_namespaces[$key] = null;
             }
 
@@ -221,10 +221,10 @@ function (Attribute $attr) {
             // All attributes must be namespaced, ergo non-null
             Assert::allNotNull($actual_namespaces);
 
-            if ($namespace === C::XS_ANY_NS_OTHER) {
+            if ($namespace === NS::OTHER) {
                 // Must be any namespace other than the parent element
                 Assert::allNotSame($actual_namespaces, static::NS);
-            } elseif ($namespace === C::XS_ANY_NS_TARGET) {
+            } elseif ($namespace === NS::TARGET) {
                 // Must be the same namespace as the one of the parent element
                 Assert::allSame($actual_namespaces, static::NS);
             }
@@ -236,9 +236,9 @@ function (Attribute $attr) {
 
 
     /**
-     * @return array|string
+     * @return array|\SimpleSAML\XML\XsNamespace
      */
-    public function getAttributeNamespace(): array|string
+    public function getAttributeNamespace(): array|NS
     {
         Assert::true(
             defined('static::XS_ANY_ATTR_NAMESPACE'),
diff --git a/src/ExtendableElementTrait.php b/src/ExtendableElementTrait.php
index 9f2dfa4..ead62b8 100644
--- a/src/ExtendableElementTrait.php
+++ b/src/ExtendableElementTrait.php
@@ -9,6 +9,7 @@
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\Chunk;
 use SimpleSAML\XML\Constants as C;
+use SimpleSAML\XML\XsNamespace as NS;
 
 use function array_diff;
 use function array_map;
@@ -45,12 +46,12 @@ protected function setElements(array $elements): void
         // Validate namespace value
         if (!is_array($namespace)) {
             // Must be one of the predefined values
-            Assert::oneOf($namespace, C::XS_ANY_NS);
+            Assert::oneOf($namespace, NS::cases());
         } else {
             // Array must be non-empty and cannot contain ##any or ##other
             Assert::notEmpty($namespace);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_ANY);
-            Assert::allNotSame($namespace, C::XS_ANY_NS_OTHER);
+            Assert::allNotSame($namespace, NS::ANY);
+            Assert::allNotSame($namespace, NS::OTHER);
         }
 
         // Get namespaces for all elements
@@ -66,7 +67,7 @@ function (ElementInterface $elt) {
             $elements
         );
 
-        if ($namespace === C::XS_ANY_NS_LOCAL) {
+        if ($namespace === NS::LOCAL) {
             // If ##local then all namespaces must be null
             Assert::allNull($actual_namespaces);
         } elseif (is_array($namespace)) {
@@ -74,12 +75,12 @@ function (ElementInterface $elt) {
             $allowed_namespaces = $namespace;
 
             // Replace the ##targetedNamespace with the actual namespace
-            if (($key = array_search(C::XS_ANY_NS_TARGET, $allowed_namespaces)) !== false) {
+            if (($key = array_search(NS::TARGET, $allowed_namespaces)) !== false) {
                 $allowed_namespaces[$key] = static::NS;
             }
 
             // Replace the ##local with null
-            if (($key = array_search(C::XS_ANY_NS_LOCAL, $allowed_namespaces)) !== false) {
+            if (($key = array_search(NS::LOCAL, $allowed_namespaces)) !== false) {
                 $allowed_namespaces[$key] = null;
             }
 
@@ -92,11 +93,11 @@ function (ElementInterface $elt) {
                     static::NS,
                 ),
             );
-        } elseif ($namespace === C::XS_ANY_NS_OTHER) {
+        } elseif ($namespace === NS::OTHER) {
             // Must be any namespace other than the parent element, excluding elements with no namespace
             Assert::notInArray(null, $actual_namespaces);
             Assert::allNotSame($actual_namespaces, static::NS);
-        } elseif ($namespace === C::XS_ANY_NS_TARGET) {
+        } elseif ($namespace === NS::TARGET) {
             // Must be the same namespace as the one of the parent element
             Assert::allSame($actual_namespaces, static::NS);
         } else {
@@ -119,9 +120,9 @@ public function getElements(): array
 
 
     /**
-     * @return array|string
+     * @return array|\SimpleSAML\XML\XsNamespace
      */
-    public function getElementNamespace(): array|string
+    public function getElementNamespace(): array|NS
     {
         Assert::true(
             defined('static::XS_ANY_ELT_NAMESPACE'),
diff --git a/src/XsNamespace.php b/src/XsNamespace.php
new file mode 100644
index 0000000..3d4170b
--- /dev/null
+++ b/src/XsNamespace.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML;
+
+/**
+ * The namespace-attribute values for xs:any elements
+ *
+ * @package simplesamlphp/xml-common
+ */
+enum XsNamespace: string
+{
+    case ANY = '##any';
+    case LOCAL = '##local';
+    case OTHER = '##other';
+    case TARGET = '##targetNamespace';
+}
diff --git a/src/XsProcess.php b/src/XsProcess.php
new file mode 100644
index 0000000..762c4d7
--- /dev/null
+++ b/src/XsProcess.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML;
+
+/**
+ * The processContents-attribute values for xs:any elements
+ *
+ * @package simplesamlphp/xml-common
+ */
+enum XsProcess: string
+{
+    case LAX = 'lax';
+    case SKIP = 'skip';
+    case STRICT = 'strict';
+}
diff --git a/tests/Utils/ExtendableAttributesElement.php b/tests/Utils/ExtendableAttributesElement.php
index 0ec6db5..368d657 100644
--- a/tests/Utils/ExtendableAttributesElement.php
+++ b/tests/Utils/ExtendableAttributesElement.php
@@ -8,7 +8,7 @@
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\Assert\AssertionFailedException;
 use SimpleSAML\XML\AbstractElement;
-use SimpleSAML\XML\Constants as C;
+use SimpleSAML\XML\XsNamespace as NS;
 use SimpleSAML\XML\ExtendableAttributesTrait;
 use SimpleSAML\XML\Exception\InvalidDOMElementException;
 
@@ -32,7 +32,7 @@ class ExtendableAttributesElement extends AbstractElement
     public const LOCALNAME = 'ExtendableAttributesElement';
 
     /** @var string|array */
-    public const XS_ANY_ATTR_NAMESPACE = C::XS_ANY_NS_ANY;
+    public const XS_ANY_ATTR_NAMESPACE = NS::ANY;
 
 
     /**
diff --git a/tests/Utils/ExtendableElement.php b/tests/Utils/ExtendableElement.php
index 6fb32f2..9ba5166 100644
--- a/tests/Utils/ExtendableElement.php
+++ b/tests/Utils/ExtendableElement.php
@@ -8,7 +8,7 @@
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\AbstractElement;
 use SimpleSAML\XML\Chunk;
-use SimpleSAML\XML\Constants as C;
+use SimpleSAML\XML\XsNamespace as NS;
 use SimpleSAML\XML\ExtendableElementTrait;
 use SimpleSAML\XML\Exception\InvalidDOMElementException;
 use SimpleSAML\XML\SerializableElementTrait;
@@ -33,8 +33,8 @@ class ExtendableElement extends AbstractElement
     /** @var string */
     public const LOCALNAME = 'ExtendableElement';
 
-    /** @var string|array */
-    public const XS_ANY_ELT_NAMESPACE = C::XS_ANY_NS_ANY;
+    /** @var \SimpleSAML\XML\XsNamespace|array */
+    public const XS_ANY_ELT_NAMESPACE = NS::ANY;
 
 
     /**
diff --git a/tests/XML/ExtendableAttributesTest.php b/tests/XML/ExtendableAttributesTest.php
index c01c717..833d174 100644
--- a/tests/XML/ExtendableAttributesTest.php
+++ b/tests/XML/ExtendableAttributesTest.php
@@ -6,10 +6,10 @@
 
 use PHPUnit\Framework\TestCase;
 use SimpleSAML\Test\XML\ExtendableAttributesElement;
+use SimpleSAML\XML\Attribute;
 use SimpleSAML\XML\DOMDocumentFactory;
 use SimpleSAML\XML\TestUtils\SchemaValidationTestTrait;
 use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
-use SimpleSAML\XML\Attribute;
 
 use function dirname;
 
diff --git a/tests/XML/ExtendableAttributesTraitTest.php b/tests/XML/ExtendableAttributesTraitTest.php
index 5f16d4f..a5cb94f 100644
--- a/tests/XML/ExtendableAttributesTraitTest.php
+++ b/tests/XML/ExtendableAttributesTraitTest.php
@@ -9,9 +9,9 @@
 use SimpleSAML\Assert\AssertionFailedException;
 use SimpleSAML\Test\XML\ExtendableAttributesElement;
 use SimpleSAML\Test\XML\ExtendableAttributesTestTrait;
-use SimpleSAML\XML\Constants as C;
-use SimpleSAML\XML\DOMDocumentFactory;
 use SimpleSAML\XML\Attribute;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\XsNamespace as NS;
 
 use function dirname;
 
@@ -70,29 +70,15 @@ public function testGetAttributeNS(): void
     }
 
 
-    /**
-     */
-    public function testInvalidNamespaceThrowsAnException(): void
-    {
-        $this->expectException(AssertionFailedException::class);
-        new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
-            {
-                return 'wrong';
-            }
-        };
-    }
-
-
     /**
      */
     public function testIllegalNamespaceComboThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_OTHER, C::XS_ANY_NS_ANY];
+                return [NS::OTHER, NS::ANY];
             }
         };
     }
@@ -102,7 +88,7 @@ public function testEmptyNamespaceArrayThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
                 return [];
             }
@@ -115,13 +101,13 @@ public function getAttributeNamespace(): array|string
     public function testOtherNamespacePassingOtherSucceeds(): void
     {
         $c = new class ([self::$other]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_OTHER;
+                return NS::OTHER;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_OTHER, $c->getAttributeNamespace());
+        $this->assertEquals(NS::OTHER, $c->getAttributeNamespace());
     }
 
 
@@ -131,9 +117,9 @@ public function testOtherNamespacePassingLocalThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$local]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_OTHER;
+                return NS::OTHER;
             }
         };
     }
@@ -144,13 +130,13 @@ public function getAttributeNamespace(): array|string
     public function testTargetNamespacePassingTargetSucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_TARGET;
+                return NS::TARGET;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_TARGET, $c->getAttributeNamespace());
+        $this->assertEquals(NS::TARGET, $c->getAttributeNamespace());
     }
 
 
@@ -159,13 +145,13 @@ public function getAttributeNamespace(): array|string
     public function testTargetNamespacePassingTargetArraySucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_TARGET];
+                return [NS::TARGET];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_TARGET], $c->getAttributeNamespace());
+        $this->assertEquals([NS::TARGET], $c->getAttributeNamespace());
     }
 
 
@@ -174,13 +160,13 @@ public function getAttributeNamespace(): array|string
     public function testTargetNamespacePassingTargetArraySucceedsWithLocal(): void
     {
         $c = new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_TARGET, C::XS_ANY_NS_LOCAL];
+                return [NS::TARGET, NS::LOCAL];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_TARGET, C::XS_ANY_NS_LOCAL], $c->getAttributeNamespace());
+        $this->assertEquals([NS::TARGET, NS::LOCAL], $c->getAttributeNamespace());
     }
 
 
@@ -190,9 +176,9 @@ public function testTargetNamespacePassingOtherThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$other]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_TARGET;
+                return NS::TARGET;
             }
         };
     }
@@ -203,13 +189,13 @@ public function getAttributeNamespace(): array|string
     public function testLocalNamespacePassingLocalSucceeds(): void
     {
         $c = new class ([self::$local]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_LOCAL, $c->getAttributeNamespace());
+        $this->assertEquals(NS::LOCAL, $c->getAttributeNamespace());
     }
 
 
@@ -218,13 +204,13 @@ public function getAttributeNamespace(): array|string
     public function testLocalNamespacePassingLocalArraySucceeds(): void
     {
         $c = new class ([self::$local]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_LOCAL];
+                return [NS::LOCAL];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_LOCAL], $c->getAttributeNamespace());
+        $this->assertEquals([NS::LOCAL], $c->getAttributeNamespace());
     }
 
 
@@ -234,9 +220,9 @@ public function testLocalNamespacePassingTargetThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAtributeNamespace(): array|string
+            public function getAtributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
     }
@@ -249,9 +235,9 @@ public function testLocalNamespacePassingOtherThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$other]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
     }
@@ -262,13 +248,13 @@ public function getAttributeNamespace(): array|string
     public function testAnyNamespacePassingTargetSucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_ANY;
+                return NS::ANY;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_ANY, $c->getAttributeNamespace());
+        $this->assertEquals(NS::ANY, $c->getAttributeNamespace());
     }
 
 
@@ -277,12 +263,12 @@ public function getAttributeNamespace(): array|string
     public function testAnyNamespacePassingOtherSucceeds(): void
     {
         $c = new class ([self::$other]) extends ExtendableAttributesElement {
-            public function getAttributeNamespace(): array|string
+            public function getAttributeNamespace(): array|NS
             {
-                return C::XS_ANY_NS_ANY;
+                return NS::ANY;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_ANY, $c->getAttributeNamespace());
+        $this->assertEquals(NS::ANY, $c->getAttributeNamespace());
     }
 }
diff --git a/tests/XML/ExtendableElementTraitTest.php b/tests/XML/ExtendableElementTraitTest.php
index fe6cccd..c2efe83 100644
--- a/tests/XML/ExtendableElementTraitTest.php
+++ b/tests/XML/ExtendableElementTraitTest.php
@@ -8,9 +8,9 @@
 use SimpleSAML\Assert\AssertionFailedException;
 use SimpleSAML\Test\XML\ExtendableElement;
 use SimpleSAML\XML\Chunk;
-use SimpleSAML\XML\Constants as C;
 use SimpleSAML\XML\DOMDocumentFactory;
 use SimpleSAML\XML\ElementInterface;
+use SimpleSAML\XML\XsNamespace as NS;
 
 use function dirname;
 
@@ -64,29 +64,15 @@ public static function setUpBeforeClass(): void
     }
 
 
-    /**
-     */
-    public function testInvalidNamespaceThrowsAnException(): void
-    {
-        $this->expectException(AssertionFailedException::class);
-        new class ([]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
-            {
-                return 'wrong';
-            }
-        };
-    }
-
-
     /**
      */
     public function testIllegalNamespaceComboThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_OTHER, C::XS_ANY_NS_ANY];
+                return [NS::OTHER, NS::ANY];
             }
         };
     }
@@ -98,7 +84,7 @@ public function testEmptyNamespaceArrayThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
                 return [];
             }
@@ -111,13 +97,13 @@ public function getElementNamespace(): array|string
     public function testOtherNamespacePassingOtherSucceeds(): void
     {
         $c = new class ([self::$other]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_OTHER;
+                return NS::OTHER;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_OTHER, $c->getElementNamespace());
+        $this->assertEquals(NS::OTHER, $c->getElementNamespace());
     }
 
 
@@ -127,9 +113,9 @@ public function testOtherNamespacePassingLocalThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$local]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_OTHER;
+                return NS::OTHER;
             }
         };
     }
@@ -140,13 +126,13 @@ public function getElementNamespace(): array|string
     public function testTargetNamespacePassingTargetSucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_TARGET;
+                return NS::TARGET;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_TARGET, $c->getElementNamespace());
+        $this->assertEquals(NS::TARGET, $c->getElementNamespace());
     }
 
 
@@ -155,13 +141,13 @@ public function getElementNamespace(): array|string
     public function testTargetNamespacePassingTargetArraySucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_TARGET];
+                return [NS::TARGET];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_TARGET], $c->getElementNamespace());
+        $this->assertEquals([NS::TARGET], $c->getElementNamespace());
     }
 
 
@@ -170,13 +156,13 @@ public function getElementNamespace(): array|string
     public function testTargetNamespacePassingTargetArraySucceedsWithLocal(): void
     {
         $c = new class ([self::$target]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_TARGET, C::XS_ANY_NS_LOCAL];
+                return [NS::TARGET, NS::LOCAL];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_TARGET, C::XS_ANY_NS_LOCAL], $c->getElementNamespace());
+        $this->assertEquals([NS::TARGET, NS::LOCAL], $c->getElementNamespace());
     }
 
 
@@ -186,9 +172,9 @@ public function testTargetNamespacePassingOtherThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$other]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_TARGET;
+                return NS::TARGET;
             }
         };
     }
@@ -199,13 +185,13 @@ public function getElementNamespace(): array|string
     public function testLocalNamespacePassingLocalSucceeds(): void
     {
         $c = new class ([self::$local]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_LOCAL, $c->getElementNamespace());
+        $this->assertEquals(NS::LOCAL, $c->getElementNamespace());
     }
 
 
@@ -214,13 +200,13 @@ public function getElementNamespace(): array|string
     public function testLocalNamespacePassingLocalArraySucceeds(): void
     {
         $c = new class ([self::$local]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return [C::XS_ANY_NS_LOCAL];
+                return [NS::LOCAL];
             }
         };
 
-        $this->assertEquals([C::XS_ANY_NS_LOCAL], $c->getElementNamespace());
+        $this->assertEquals([NS::LOCAL], $c->getElementNamespace());
     }
 
 
@@ -230,9 +216,9 @@ public function testLocalNamespacePassingTargetThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$target]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
     }
@@ -244,9 +230,9 @@ public function testLocalNamespacePassingOtherThrowsAnException(): void
     {
         $this->expectException(AssertionFailedException::class);
         new class ([self::$other]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_LOCAL;
+                return NS::LOCAL;
             }
         };
     }
@@ -257,13 +243,13 @@ public function getElementNamespace(): array|string
     public function testAnyNamespacePassingLocalSucceeds(): void
     {
         $c = new class ([self::$local]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_ANY;
+                return NS::ANY;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_ANY, $c->getElementNamespace());
+        $this->assertEquals(NS::ANY, $c->getElementNamespace());
     }
 
 
@@ -272,13 +258,13 @@ public function getElementNamespace(): array|string
     public function testAnyNamespacePassingTargetSucceeds(): void
     {
         $c = new class ([self::$target]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_ANY;
+                return NS::ANY;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_ANY, $c->getElementNamespace());
+        $this->assertEquals(NS::ANY, $c->getElementNamespace());
     }
 
 
@@ -287,12 +273,12 @@ public function getElementNamespace(): array|string
     public function testAnyNamespacePassingOtherSucceeds(): void
     {
         $c = new class ([self::$other]) extends ExtendableElement {
-            public function getElementNamespace(): array|string
+            public function getElementNamespace(): array|NS
             {
-                return C::XS_ANY_NS_ANY;
+                return NS::ANY;
             }
         };
 
-        $this->assertEquals(C::XS_ANY_NS_ANY, $c->getElementNamespace());
+        $this->assertEquals(NS::ANY, $c->getElementNamespace());
     }
 }