diff --git a/src/Assert/Assert.php b/src/Assert/Assert.php
index fcaf71f..da2e58d 100644
--- a/src/Assert/Assert.php
+++ b/src/Assert/Assert.php
@@ -9,33 +9,63 @@
 /**
  * @package simplesamlphp/xml-common
  *
+ * @method static void validDateTime(mixed $value, string $message = '', string $exception = '')
+ * @method static void validDuration(mixed $value, string $message = '', string $exception = '')
+ * @method static void validEntity(mixed $value, string $message = '', string $exception = '')
+ * @method static void validEntities(mixed $value, string $message = '', string $exception = '')
  * @method static void validHexBinary(mixed $value, string $message = '', string $exception = '')
+ * @method static void validID(mixed $value, string $message = '', string $exception = '')
+ * @method static void validIDRef(mixed $value, string $message = '', string $exception = '')
+ * @method static void validIDRefs(mixed $value, string $message = '', string $exception = '')
+ * @method static void validLang(mixed $value, string $message = '', string $exception = '')
+ * @method static void validName(mixed $value, string $message = '', string $exception = '')
+ * @method static void validNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void validNMToken(mixed $value, string $message = '', string $exception = '')
  * @method static void validNMTokens(mixed $value, string $message = '', string $exception = '')
- * @method static void validDuration(mixed $value, string $message = '', string $exception = '')
- * @method static void validDateTime(mixed $value, string $message = '', string $exception = '')
- * @method static void validNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void validQName(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidDateTime(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidDuration(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidEntity(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidEntities(mixed $value, string $message = '', string $exception = '')
  * @method static void nullOrValidHexBinary(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidID(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidIDRef(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidIDRefs(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidLang(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidName(mixed $value, string $message = '', string $exception = '')
+ * @method static void nullOrValidNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void nullOrValidNMToken(mixed $value, string $message = '', string $exception = '')
  * @method static void nullOrValidNMTokens(mixed $value, string $message = '', string $exception = '')
- * @method static void nullOrValidDuration(mixed $value, string $message = '', string $exception = '')
- * @method static void nullOrValidDateTime(mixed $value, string $message = '', string $exception = '')
- * @method static void nullOrValidNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void nullOrValidQName(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidDateTime(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidDuration(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidEntity(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidEntities(mixed $value, string $message = '', string $exception = '')
  * @method static void allValidHexBinary(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidID(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidIDRef(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidIDRefs(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidLang(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidName(mixed $value, string $message = '', string $exception = '')
+ * @method static void allValidNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void allValidNMToken(mixed $value, string $message = '', string $exception = '')
  * @method static void allValidNMTokens(mixed $value, string $message = '', string $exception = '')
- * @method static void allValidDuration(mixed $value, string $message = '', string $exception = '')
- * @method static void allValidDateTime(mixed $value, string $message = '', string $exception = '')
- * @method static void allValidNCName(mixed $value, string $message = '', string $exception = '')
  * @method static void allValidQName(mixed $value, string $message = '', string $exception = '')
  */
 class Assert extends BaseAssert
 {
     use DateTimeTrait;
     use DurationTrait;
-    use HexBinTrait;
-    use NamesTrait;
-    use TokensTrait;
+    use HexBinaryTrait;
+    use EntitiesTrait;
+    use EntityTrait;
+    use IDTrait;
+    use IDRefTrait;
+    use IDRefsTrait;
+    use LangTrait;
+    use NameTrait;
+    use NCNameTrait;
+    use NMTokenTrait;
+    use NMTokensTrait;
+    use QNameTrait;
 }
diff --git a/src/Assert/EntitiesTrait.php b/src/Assert/EntitiesTrait.php
new file mode 100644
index 0000000..76568bb
--- /dev/null
+++ b/src/Assert/EntitiesTrait.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+use function sprintf;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait EntitiesTrait
+{
+    /** @var string */
+    private static string $entities_regex = '/^([\p{L}a-zA-Z-][\w.-]*)([\s][\p{L}a-zA-Z-][\w.-]*)*$/Du';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validEntities(string $value, string $message = ''): void
+    {
+        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$entities_regex]]) === false) {
+            throw new InvalidArgumentException(sprintf(
+                $message ?: '\'%s\' is not a valid xs:ENTITIES',
+                $value,
+            ));
+        }
+    }
+}
diff --git a/src/Assert/EntityTrait.php b/src/Assert/EntityTrait.php
new file mode 100644
index 0000000..3c5b5eb
--- /dev/null
+++ b/src/Assert/EntityTrait.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait EntityTrait
+{
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validEntity(string $value, string $message = ''): void
+    {
+        Assert::validNCName(
+            $value,
+            $message ?: '\'%s\' is not a valid xs:Entity',
+            InvalidArgumentException::class,
+        );
+    }
+}
diff --git a/src/Assert/HexBinTrait.php b/src/Assert/HexBinaryTrait.php
similarity index 98%
rename from src/Assert/HexBinTrait.php
rename to src/Assert/HexBinaryTrait.php
index 68ca51a..2e36488 100644
--- a/src/Assert/HexBinTrait.php
+++ b/src/Assert/HexBinaryTrait.php
@@ -12,7 +12,7 @@
 /**
  * @package simplesamlphp/xml-common
  */
-trait HexBinTrait
+trait HexBinaryTrait
 {
     /** @var string */
     private static string $hexbin_regex = '/^([0-9a-fA-F]{2})+$/D';
diff --git a/src/Assert/IDRefTrait.php b/src/Assert/IDRefTrait.php
new file mode 100644
index 0000000..efbb963
--- /dev/null
+++ b/src/Assert/IDRefTrait.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait IDRefTrait
+{
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validIDRef(string $value, string $message = ''): void
+    {
+        Assert::validNCName(
+            $value,
+            $message ?: '\'%s\' is not a xs:IDREF',
+            InvalidArgumentException::class,
+        );
+    }
+}
diff --git a/src/Assert/IDRefsTrait.php b/src/Assert/IDRefsTrait.php
new file mode 100644
index 0000000..dcf6638
--- /dev/null
+++ b/src/Assert/IDRefsTrait.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+use function sprintf;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait IDRefsTrait
+{
+    /** @var string */
+    private static string $idrefs_regex = '/^([\p{L}a-zA-Z-][\w.-]*)([\s][\p{L}a-zA-Z-][\w.-]*)*$/Du';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validIDRefs(string $value, string $message = ''): void
+    {
+        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$idrefs_regex]]) === false) {
+            throw new InvalidArgumentException(sprintf(
+                $message ?: '\'%s\' is not a valid xs:IDREFS',
+                $value,
+            ));
+        }
+    }
+}
diff --git a/src/Assert/IDTrait.php b/src/Assert/IDTrait.php
new file mode 100644
index 0000000..2c98c6a
--- /dev/null
+++ b/src/Assert/IDTrait.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait IDTrait
+{
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validID(string $value, string $message = ''): void
+    {
+        Assert::validNCName(
+            $value,
+            $message ?: '\'%s\' is not a valid xs:ID',
+            InvalidArgumentException::class,
+        );
+    }
+}
diff --git a/src/Assert/LangTrait.php b/src/Assert/LangTrait.php
new file mode 100644
index 0000000..c98ffdd
--- /dev/null
+++ b/src/Assert/LangTrait.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+use function sprintf;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait LangTrait
+{
+    /** @var string */
+    private static string $lang_regex = '/^(i[-]|x[-])?([a-z]{1,8})([-][a-z]{1,8})?$/Di';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validLang(string $value, string $message = ''): void
+    {
+        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$lang_regex]]) === false) {
+            throw new InvalidArgumentException(sprintf(
+                $message ?: '\'%s\' is not a valid xs:language',
+                $value,
+            ));
+        }
+    }
+}
diff --git a/src/Assert/NamesTrait.php b/src/Assert/NCNameTrait.php
similarity index 62%
rename from src/Assert/NamesTrait.php
rename to src/Assert/NCNameTrait.php
index 3254913..474edee 100644
--- a/src/Assert/NamesTrait.php
+++ b/src/Assert/NCNameTrait.php
@@ -12,13 +12,10 @@
 /**
  * @package simplesamlphp/xml-common
  */
-trait NamesTrait
+trait NCNameTrait
 {
     /** @var string */
-    private static string $ncname_regex = '/^[a-zA-Z_][\w.-]*$/D';
-
-    /** @var string */
-    private static string $qname_regex = '/^[a-zA-Z_][\w.-]*:[a-zA-Z_][\w.-]*$/D';
+    private static string $ncname_regex = '/^[\p{L}a-zA-Z-][\w.-]+$/Du';
 
     /***********************************************************************************
      *  NOTE:  Custom assertions may be added below this line.                         *
@@ -42,22 +39,4 @@ protected static function validNCName(string $value, string $message = ''): void
             ));
         }
     }
-
-
-    /**
-     * @param string $value
-     * @param string $message
-     */
-    protected static function validQName(string $value, string $message = ''): void
-    {
-        if (
-            filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$qname_regex]]) === false &&
-            filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$ncname_regex]]) === false
-        ) {
-            throw new InvalidArgumentException(sprintf(
-                $message ?: '\'%s\' is not a valid qualified name (QName)',
-                $value,
-            ));
-        }
-    }
 }
diff --git a/src/Assert/NMTokenTrait.php b/src/Assert/NMTokenTrait.php
new file mode 100644
index 0000000..a0c2e9d
--- /dev/null
+++ b/src/Assert/NMTokenTrait.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+use function sprintf;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait NMTokenTrait
+{
+    /** @var string */
+    private static string $nmtoken_regex = '/^[\w.:-]+$/Du';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validNMToken(string $value, string $message = ''): void
+    {
+        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$nmtoken_regex]]) === false) {
+            throw new InvalidArgumentException(sprintf(
+                $message ?: '\'%s\' is not a valid xs:NMTOKEN',
+                $value,
+            ));
+        }
+    }
+}
diff --git a/src/Assert/TokensTrait.php b/src/Assert/NMTokensTrait.php
similarity index 71%
rename from src/Assert/TokensTrait.php
rename to src/Assert/NMTokensTrait.php
index 9ea6b1e..b1cc459 100644
--- a/src/Assert/TokensTrait.php
+++ b/src/Assert/NMTokensTrait.php
@@ -12,11 +12,8 @@
 /**
  * @package simplesamlphp/xml-common
  */
-trait TokensTrait
+trait NMTokensTrait
 {
-    /** @var string */
-    private static string $nmtoken_regex = '/^[\w.:-]+$/Du';
-
     /** @var string */
     private static string $nmtokens_regex = '/^([\w.:-]+)([\s][\w.:-]+)*$/Du';
 
@@ -29,21 +26,6 @@ trait TokensTrait
      ***********************************************************************************/
 
 
-    /**
-     * @param string $value
-     * @param string $message
-     */
-    protected static function validNMToken(string $value, string $message = ''): void
-    {
-        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$nmtoken_regex]]) === false) {
-            throw new InvalidArgumentException(sprintf(
-                $message ?: '\'%s\' is not a valid xs:NMTOKEN',
-                $value,
-            ));
-        }
-    }
-
-
     /**
      * @param string $value
      * @param string $message
diff --git a/src/Assert/NameTrait.php b/src/Assert/NameTrait.php
new file mode 100644
index 0000000..1a7d997
--- /dev/null
+++ b/src/Assert/NameTrait.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+use function sprintf;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait NameTrait
+{
+    /** @var string */
+    private static string $name_regex = '/^[a-zA-Z:-][\w.:-]+$/Du';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validName(string $value, string $message = ''): void
+    {
+        if (filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$name_regex]]) === false) {
+            throw new InvalidArgumentException(sprintf(
+                $message ?: '\'%s\' is not a valid xs:Name',
+                $value,
+            ));
+        }
+    }
+}
diff --git a/src/Assert/QNameTrait.php b/src/Assert/QNameTrait.php
new file mode 100644
index 0000000..bb4be8f
--- /dev/null
+++ b/src/Assert/QNameTrait.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Assert;
+
+use InvalidArgumentException;
+
+use function filter_var;
+
+/**
+ * @package simplesamlphp/xml-common
+ */
+trait QNameTrait
+{
+    /** @var string */
+    private static string $qname_regex = '/^[a-zA-Z_][\w.-]*:[a-zA-Z_][\w.-]*$/D';
+
+    /***********************************************************************************
+     *  NOTE:  Custom assertions may be added below this line.                         *
+     *         They SHOULD be marked as `protected` to ensure the call is forced       *
+     *          through __callStatic().                                                *
+     *         Assertions marked `public` are called directly and will                 *
+     *          not handle any custom exception passed to it.                          *
+     ***********************************************************************************/
+
+
+    /**
+     * @param string $value
+     * @param string $message
+     */
+    protected static function validQName(string $value, string $message = ''): void
+    {
+        if (
+            filter_var($value, FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => self::$qname_regex]]) === false
+        ) {
+            Assert::validNCName(
+                $value,
+                $message ?: '\'%s\' is not a valid qualified name (QName)',
+                InvalidArgumentException::class,
+            );
+        }
+    }
+}
diff --git a/src/Type/AbstractValueType.php b/src/Type/AbstractValueType.php
new file mode 100644
index 0000000..3ced6c3
--- /dev/null
+++ b/src/Type/AbstractValueType.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * Abstract class to be implemented by all types
+ *
+ * @package simplesamlphp/xml-common
+ */
+abstract class AbstractValueType implements ValueTypeInterface
+{
+    /**
+     * Set the value for this type.
+     *
+     * @param string $value
+     */
+    final protected function __construct(
+        protected string $value,
+    ) {
+        $this->validateValue($value);
+    }
+
+
+    /**
+     * Get the value.
+     *
+     * @return string
+     */
+    public function getValue(): string
+    {
+        return $this->sanitizeValue($this->getRawValue());
+    }
+
+
+    /**
+     * Get the raw unsanitized value.
+     *
+     * @return string
+     */
+    public function getRawValue(): string
+    {
+        return $this->value;
+    }
+
+
+    /**
+     * Sanitize the value.
+     *
+     * @param string $value  The value
+     * @throws \Exception on failure
+     * @return string
+     */
+    protected function sanitizeValue(string $value): string
+    {
+        /**
+         * Perform no sanitation by default.
+         * Override this method on the implementing class to perform content sanitation.
+         */
+        return $value;
+    }
+
+
+    /**
+     * Validate the value.
+     *
+     * @param string $value  The value
+     * @throws \Exception on failure
+     * @return void
+     */
+    protected function validateValue(/** @scrutinizer ignore-unused */ string $value): void
+    {
+        /**
+         * Perform no validation by default.
+         * Override this method on the implementing class to perform validation.
+         */
+    }
+
+
+    /**
+     * @param string $value
+     * @return \SimpleSAML\XML\Type\ValueTypeInterface
+     */
+    public static function fromString(string $value): ValueTypeInterface
+    {
+        return new static($value);
+    }
+
+
+    /**
+     * Output the value as a string
+     *
+     * @return string
+     */
+    public function __toString(): string
+    {
+        return $this->getValue();
+    }
+}
diff --git a/src/Type/Base64Value.php b/src/Type/Base64Value.php
new file mode 100644
index 0000000..d9e7f1a
--- /dev/null
+++ b/src/Type/Base64Value.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+use function str_replace;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class Base64Value extends AbstractValueType
+{
+    /**
+     * Sanitize the value.
+     *
+     * Note:  There are no processing rules for xs:base64 regarding whitespace. General consensus is to strip them
+     *
+     * @param string $value  The unsanitized value
+     * @return string
+     */
+    protected function sanitizeValue(string $value): string
+    {
+        return str_replace(["\f", "\r", "\n", "\t", "\v", ' '], '', $value);
+    }
+
+
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validBase64($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/DateTimeValue.php b/src/Type/DateTimeValue.php
new file mode 100644
index 0000000..783d442
--- /dev/null
+++ b/src/Type/DateTimeValue.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class DateTimeValue extends AbstractValueType
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        Assert::validDateTime($value, SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/DurationValue.php b/src/Type/DurationValue.php
new file mode 100644
index 0000000..8b4d388
--- /dev/null
+++ b/src/Type/DurationValue.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class DurationValue extends AbstractValueType
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        Assert::validDuration($value, SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/EntitiesValue.php b/src/Type/EntitiesValue.php
new file mode 100644
index 0000000..05c0014
--- /dev/null
+++ b/src/Type/EntitiesValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class EntitiesValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validEntities($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/EntityValue.php b/src/Type/EntityValue.php
new file mode 100644
index 0000000..6970a3e
--- /dev/null
+++ b/src/Type/EntityValue.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class EntityValue extends NCNameValue
+{
+}
diff --git a/src/Type/HexBinaryValue.php b/src/Type/HexBinaryValue.php
new file mode 100644
index 0000000..744d7f6
--- /dev/null
+++ b/src/Type/HexBinaryValue.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+use function str_replace;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class HexBinaryValue extends AbstractValueType
+{
+    /**
+     * Sanitize the value.
+     *
+     * Note:  There are no processing rules for xs:hexBinary regarding whitespace. General consensus is to strip them
+     *
+     * @param string $value  The unsanitized value
+     * @return string
+     */
+    protected function sanitizeValue(string $value): string
+    {
+        return str_replace(["\f", "\r", "\n", "\t", "\v", ' '], '', $value);
+    }
+
+
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::regex(
+            $this->sanitizeValue($value),
+            '/([0-9A-F]{2})*/i',
+            SchemaViolationException::class,
+        );
+    }
+}
diff --git a/src/Type/IDRefValue.php b/src/Type/IDRefValue.php
new file mode 100644
index 0000000..bc4ebe8
--- /dev/null
+++ b/src/Type/IDRefValue.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class IDRefValue extends NCNameValue
+{
+}
diff --git a/src/Type/IDRefsValue.php b/src/Type/IDRefsValue.php
new file mode 100644
index 0000000..b489181
--- /dev/null
+++ b/src/Type/IDRefsValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class IDRefsValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validIDRefs($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/IDValue.php b/src/Type/IDValue.php
new file mode 100644
index 0000000..1863014
--- /dev/null
+++ b/src/Type/IDValue.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class IDValue extends NCNameValue
+{
+}
diff --git a/src/Type/IntegerValue.php b/src/Type/IntegerValue.php
new file mode 100644
index 0000000..e24ff85
--- /dev/null
+++ b/src/Type/IntegerValue.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class IntegerValue extends AbstractValueType
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        Assert::numeric($value, SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/LangValue.php b/src/Type/LangValue.php
new file mode 100644
index 0000000..d4046c3
--- /dev/null
+++ b/src/Type/LangValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class LangValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: content must already be sanitized before validating
+        Assert::validLang($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/NCNameValue.php b/src/Type/NCNameValue.php
new file mode 100644
index 0000000..8571249
--- /dev/null
+++ b/src/Type/NCNameValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class NCNameValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validNCName($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/NMTokenValue.php b/src/Type/NMTokenValue.php
new file mode 100644
index 0000000..704f66d
--- /dev/null
+++ b/src/Type/NMTokenValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class NMTokenValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validNMToken($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/NMTokensValue.php b/src/Type/NMTokensValue.php
new file mode 100644
index 0000000..71c8394
--- /dev/null
+++ b/src/Type/NMTokensValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class NMTokensValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validNMTokens($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/NameValue.php b/src/Type/NameValue.php
new file mode 100644
index 0000000..6e8a8ae
--- /dev/null
+++ b/src/Type/NameValue.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class NameValue extends TokenValue
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        // Note: value must already be sanitized before validating
+        Assert::validName($this->sanitizeValue($value), SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/NormalizedStringValue.php b/src/Type/NormalizedStringValue.php
new file mode 100644
index 0000000..1aa1ee8
--- /dev/null
+++ b/src/Type/NormalizedStringValue.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use function str_replace;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class NormalizedStringValue extends StringValue
+{
+    /**
+     * Sanitize the value.
+     *
+     * @param string $value  The unsanitized value
+     * @return string
+     */
+    protected function sanitizeValue(string $value): string
+    {
+        return str_replace(["\f", "\r", "\n", "\t", "\v"], ' ', $value);
+    }
+}
diff --git a/src/Type/StringValue.php b/src/Type/StringValue.php
new file mode 100644
index 0000000..b4bf799
--- /dev/null
+++ b/src/Type/StringValue.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class StringValue extends AbstractValueType
+{
+}
diff --git a/src/Type/TokenValue.php b/src/Type/TokenValue.php
new file mode 100644
index 0000000..2c2595d
--- /dev/null
+++ b/src/Type/TokenValue.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use function preg_replace;
+use function trim;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class TokenValue extends NormalizedStringValue
+{
+    /**
+     * Sanitize the value.
+     *
+     * @param string $value  The unsanitized value
+     * @return string
+     */
+    protected function sanitizeValue(string $value): string
+    {
+        $content = parent::sanitizeValue($value);
+        return trim(preg_replace('/\s+/', ' ', $value));
+    }
+}
diff --git a/src/Type/URIValue.php b/src/Type/URIValue.php
new file mode 100644
index 0000000..73ca0fc
--- /dev/null
+++ b/src/Type/URIValue.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+use SimpleSAML\XML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+
+/**
+ * @package simplesaml/xml-common
+ */
+class URIValue extends AbstractValueType
+{
+    /**
+     * Validate the value.
+     *
+     * @param string $value
+     * @throws \SimpleSAML\XML\Exception\SchemaViolationException on failure
+     * @return void
+     */
+    protected function validateValue(string $value): void
+    {
+        Assert::validURI($value, SchemaViolationException::class);
+    }
+}
diff --git a/src/Type/ValueTypeInterface.php b/src/Type/ValueTypeInterface.php
new file mode 100644
index 0000000..baf981f
--- /dev/null
+++ b/src/Type/ValueTypeInterface.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XML\Type;
+
+/**
+ * interface class to be implemented by all the classes that represent a value type
+ *
+ * @package simplesamlphp/xml-common
+ */
+interface ValueTypeInterface
+{
+    /**
+     * @return string
+     */
+    public function getValue(): string;
+
+
+    /**
+     * @param string $value
+     * @return \SimpleSAML\XML\Type\ValueTypeInterface
+     */
+    public static function fromString(string $value): ValueTypeInterface;
+}
diff --git a/src/Utils.php b/src/Utils.php
index 2c00961..40e592c 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -7,7 +7,7 @@
 use DateTimeImmutable;
 use DateTimeInterface;
 use DOMElement;
-use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Assert\Assert;
 
 use function trim;
 
diff --git a/tests/Assert/EntitiesTest.php b/tests/Assert/EntitiesTest.php
new file mode 100644
index 0000000..0005bf8
--- /dev/null
+++ b/tests/Assert/EntitiesTest.php
@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\EntitiesTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class EntitiesTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $entities
+     */
+    #[DataProvider('provideEntities')]
+    public function testValidEntities(bool $shouldPass, string $entities): void
+    {
+        try {
+            Assert::validEntities($entities);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideEntities(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, 'CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            [false, '0836217462 0836217463'],
+            [true, 'foo bar'],
+            // Quotes are forbidden
+            [false, 'foo "bar" baz'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Assert/EntityTest.php b/tests/Assert/EntityTest.php
new file mode 100644
index 0000000..b7488f8
--- /dev/null
+++ b/tests/Assert/EntityTest.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\EntityTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class EntityTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $entity
+     */
+    #[DataProvider('provideEntity')]
+    public function testValidEntity(bool $shouldPass, string $entity): void
+    {
+        try {
+            Assert::validEntity($entity);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideEntity(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, 'CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            [false, '0836217462'],
+            // Spaces are forbidden
+            [false, 'foo bar'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Assert/HexBinTest.php b/tests/Assert/HexBinaryTest.php
similarity index 97%
rename from tests/Assert/HexBinTest.php
rename to tests/Assert/HexBinaryTest.php
index 042e7ce..76deff6 100644
--- a/tests/Assert/HexBinTest.php
+++ b/tests/Assert/HexBinaryTest.php
@@ -7,8 +7,8 @@
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
-use SimpleSAML\Assert\Assert;
 use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
 
 /**
  * Class \SimpleSAML\Test\Assert\HexBinaryTest
diff --git a/tests/Assert/IDRefTest.php b/tests/Assert/IDRefTest.php
new file mode 100644
index 0000000..c5c25cf
--- /dev/null
+++ b/tests/Assert/IDRefTest.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\IDRefTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class IDRefTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $idref
+     */
+    #[DataProvider('provideIDRef')]
+    public function testValidIDRef(bool $shouldPass, string $idref): void
+    {
+        try {
+            Assert::validIDRef($idref);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideIDRef(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, 'CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            [false, '0836217462'],
+            // Spaces are forbidden
+            [false, 'foo bar'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Assert/IDRefsTest.php b/tests/Assert/IDRefsTest.php
new file mode 100644
index 0000000..d12cc73
--- /dev/null
+++ b/tests/Assert/IDRefsTest.php
@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\IDRefsTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class IDRefsTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $idrefs
+     */
+    #[DataProvider('provideIDRefs')]
+    public function testValidIDRefs(bool $shouldPass, string $idrefs): void
+    {
+        try {
+            Assert::validIDRefs($idrefs);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideIDRefs(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, 'CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            [false, '0836217462 0836217463'],
+            [true, 'foo bar'],
+            // Quotes are forbidden
+            [false, 'foo "bar" baz'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Assert/IDTest.php b/tests/Assert/IDTest.php
new file mode 100644
index 0000000..d333c2e
--- /dev/null
+++ b/tests/Assert/IDTest.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\IDTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class IDTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $id
+     */
+    #[DataProvider('provideID')]
+    public function testValidID(bool $shouldPass, string $id): void
+    {
+        try {
+            Assert::validID($id);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideID(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, 'CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            [false, '0836217462'],
+            // Spaces are forbidden
+            [false, 'foo bar'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Assert/LangTest.php b/tests/Assert/LangTest.php
new file mode 100644
index 0000000..25468a6
--- /dev/null
+++ b/tests/Assert/LangTest.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\LangTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class LangTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $lang
+     */
+    #[DataProvider('provideLang')]
+    public function testValidLang(bool $shouldPass, string $lang): void
+    {
+        try {
+            Assert::validLang($lang);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<string, array{0: bool, 1: string}>
+     */
+    public static function provideLang(): array
+    {
+        return [
+            'one part' => [true, 'lang'],
+            'two parts' => [true, 'en-US'],
+            'too many parts' => [false, 'not-a-lang'],
+            'too long' => [false, 'toolonglanguage'],
+            'x-case' => [true, 'x-klingon'],
+            'i-case' => [true, 'i-sami-no'],
+        ];
+    }
+}
diff --git a/tests/Assert/NCNameTest.php b/tests/Assert/NCNameTest.php
index f3df64e..3d81db4 100644
--- a/tests/Assert/NCNameTest.php
+++ b/tests/Assert/NCNameTest.php
@@ -41,9 +41,12 @@ public static function provideNCName(): array
     {
         return [
             [true, 'Test'],
-            [true, '_Test'],
+            [true, 'Te.st'],
+            [false, '_Test'],
+            [true, '-1950-10-04-10-00'],
+            [true, 'fööbár'],
             // Prefixed v4 UUID
-            [true, '_5425e58e-e799-4884-92cc-ca64ecede32f'],
+            [false, '_5425e58e-e799-4884-92cc-ca64ecede32f'],
             // An empty value is not valid, unless xsi:nil is used
             [false, ''],
             [false, 'Te*st'],
diff --git a/tests/Assert/NameTest.php b/tests/Assert/NameTest.php
new file mode 100644
index 0000000..6f3adbc
--- /dev/null
+++ b/tests/Assert/NameTest.php
@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Assert;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\Assert\Assert;
+
+/**
+ * Class \SimpleSAML\Test\XML\Assert\NameTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(Assert::class)]
+final class NameTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $name
+     */
+    #[DataProvider('provideName')]
+    public function testValidToken(bool $shouldPass, string $name): void
+    {
+        try {
+            Assert::validName($name);
+            $this->assertTrue($shouldPass);
+        } catch (AssertionFailedException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<int, array{0: bool, 1: string}>
+     */
+    public static function provideName(): array
+    {
+        return [
+            [true, 'Snoopy'],
+            [true, ':CMS'],
+            [true, 'fööbár'],
+            [true, '-1950-10-04'],
+            // Must start with a letter, a dash or a colon
+            [false, '0836217462'],
+            // Spaces are forbidden
+            [false, 'foo bar'],
+            // Commas are forbidden
+            [false, 'foo,bar'],
+            // Trailing newlines are forbidden
+            [false, "foobar\n"],
+        ];
+    }
+}
diff --git a/tests/Type/LangValueTest.php b/tests/Type/LangValueTest.php
new file mode 100644
index 0000000..ec2c401
--- /dev/null
+++ b/tests/Type/LangValueTest.php
@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\XML\Type;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\Type\{AbstractValueType, LangValue, TokenValue};
+
+/**
+ * Class \SimpleSAML\Test\Type\LangValueTest
+ *
+ * @package simplesamlphp/xml-common
+ */
+#[CoversClass(AbstractValueType::class)]
+#[CoversClass(TokenValue::class)]
+#[CoversClass(LangValue::class)]
+final class LangValueTest extends TestCase
+{
+    /**
+     * @param boolean $shouldPass
+     * @param string $lang
+     */
+    #[DataProvider('provideLang')]
+    public function testLang(bool $shouldPass, string $lang): void
+    {
+        try {
+            LangValue::fromString($lang);
+            $this->assertTrue($shouldPass);
+        } catch (SchemaViolationException $e) {
+            $this->assertFalse($shouldPass);
+        }
+    }
+
+
+    /**
+     * @return array<string, array{0: bool, 1: string}>
+     */
+    public static function provideLang(): array
+    {
+        return [
+            'one part' => [true, 'lang'],
+            'two parts' => [true, 'en-US'],
+            'too many parts' => [false, 'not-a-lang'],
+            'too long' => [false, 'toolonglanguage'],
+            'x-case' => [true, 'x-klingon'],
+            'i-case' => [true, 'i-sami-no'],
+            'normalization' => [true, ' en-US '],
+        ];
+    }
+}