diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index 4ece99a5..b58d8ebd 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -42,19 +42,19 @@ jobs:
           version: '${{ matrix.fhir-version }}'
 
 
-  load-fhir-validator:
-    runs-on: ubuntu-22.04
-    name: 'Download FHIR Validator'
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: ./.github/actions/load-fhir-validator
+#  load-fhir-validator:
+#    runs-on: ubuntu-22.04
+#    name: 'Download FHIR Validator'
+#    steps:
+#      - uses: actions/checkout@v4
+#
+#      - uses: ./.github/actions/load-fhir-validator
 
   run:
     runs-on: ubuntu-22.04
     needs:
       - load-fhir-source
-      - load-fhir-validator
+#      - load-fhir-validator
     strategy:
       fail-fast: false
       matrix:
@@ -77,8 +77,8 @@ jobs:
         with:
           version: '${{ matrix.fhir-version }}'
 
-      - name: 'Install FHIR validator'
-        uses: ./.github/actions/load-fhir-validator
+#      - name: 'Install FHIR validator'
+#        uses: ./.github/actions/load-fhir-validator
 
       - name: 'Install PHP'
         uses: shivammathur/setup-php@v2
@@ -123,11 +123,11 @@ jobs:
         run: |
           ./bin/generate.sh --useExisting --versions '${{ matrix.fhir-version }}'
 
-      - name: 'Install Java'
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'zulu'
-          java-version: 18
+#      - name: 'Install Java'
+#        uses: actions/setup-java@v4
+#        with:
+#          distribution: 'zulu'
+#          java-version: 18
 
       - name: 'Run tests'
         # language=sh
diff --git a/README.md b/README.md
index fa6c52eb..285a5b60 100644
--- a/README.md
+++ b/README.md
@@ -168,7 +168,9 @@ require 'path to PHPFHIRResponseParser.php';
 // build config
 $config = new \YourConfiguredNamespace\PHPFHIRResponseParserConfig([
     'registerAutoloader' => true, // use if you are not using Composer
-    'libxmlOpts' => LIBXML_COMPACT | LIBXML_NSCLEAN // choose different libxml arguments if you want, ymmv.
+    'libxmlOpts' => LIBXML_NONET | LIBXML_BIGLINES | LIBXML_PARSEHUGE | LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD | LIBXML_NOXMLDECL // choose different libxml arguments if you want, ymmv.
+    'rootXmlns' => 'https://hl7.org/fhir', // a specific root xmlns to use, if the source does not return one
+    'overrideSourceXmlns' => true, // set this to true if you want the 'rootXmlns' value you defined to override any value seen from source 
 ]);
 
 // build parser
@@ -190,14 +192,19 @@ $json = json_encode($object);
 ## XML Serialization
 
 ```php
-// To get an instance of \DOMElement...
-$element = $object->xmlSerialize();
+// To get an instance of \XMLWriter...
+$xw = $object->xmlSerialize(null, $yourConfigInstance);
 
 // to get as XML string...
-$xml = $element->ownerDocument->saveXML($element);
+$xml = $xw->outputMemory(true);
+
+// you can alternatively have the output written directly to a file:
+$xw = new \YourConfiguredNamespace\PHPFHIRXmlWriter();
+$xw->openUri('file:///some/directory/fhir-resource.xml');
+$object->xmlSerialize($xw, $yourConfigInstance);
 ```
 
-XML Serialization utilizes [DOM](https://www.php.net/manual/en/book.dom.php).
+XML Serialization utilizes [XMLWriter](https://www.php.net/manual/en/book.xmlwriter.php).
 
 # Testing
 
diff --git a/bin/generate.php b/bin/generate.php
index 5b417c92..127697f6 100644
--- a/bin/generate.php
+++ b/bin/generate.php
@@ -384,7 +384,8 @@ function is_dir_empty(string $dir): bool
 
     $url = $build_config->getUrl();
 
-    $namespace = $build_config->getNamespace(true);
+    // build vars
+    $namespace = $build_config->getFullyQualifiedName(true);
     $version = trim($version);
     $schema_dir = $config->getSchemaPath() . DIRECTORY_SEPARATOR . $version;
 
diff --git a/composer.json b/composer.json
index fc32cec4..691924ca 100644
--- a/composer.json
+++ b/composer.json
@@ -20,14 +20,16 @@
   ],
   "require": {
     "php": "^8.1",
-    "ext-simplexml": "*",
     "ext-json": "*",
     "ext-libxml": "*",
-    "ext-dom": "*",
+    "ext-simplexml": "*",
     "psr/log": "^3.0"
   },
   "require-dev": {
     "ext-curl": "*",
+    "ext-dom": "*",
+    "ext-xmlreader": "*",
+    "ext-xmlwriter": "*",
     "phpunit/phpunit": "^10.5 || ^11.0",
     "monolog/monolog": "^3.2.0"
   },
diff --git a/files/constants.php b/files/constants.php
index 99402777..a59c8030 100644
--- a/files/constants.php
+++ b/files/constants.php
@@ -85,11 +85,10 @@
 const PHPFHIR_CLASSNAME_TYPEMAP = 'PHPFHIRTypeMap';
 const PHPFHIR_CLASSNAME_DEBUG_CLIENT = 'PHPFHIRDebugClient';
 const PHPFHIR_CLASSNAME_DEBUG_CLIENT_RESPONSE = 'PHPFHIRDebugClientResponse';
+const PHPFHIR_CLASSNAME_XML_WRITER = 'PHPFHIRXmlWriter';
 
 // Core interface names
 const PHPFHIR_INTERFACE_TYPE = 'PHPFHIRTypeInterface';
-const PHPFHIR_INTERFACE_XML_SERIALIZABLE = 'PHPFHIRXmlSerializableInterface';
-const PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG = 'PHPFHIRXmlSerializableConfigInterface';
 const PHPFHIR_INTERFACE_CONTAINED_TYPE = 'PHPFHIRContainedTypeInterface';
 const PHPFHIR_INTERFACE_COMMENT_CONTAINER = 'PHPFHIRCommentContainerInterface';
 const PHPFHIR_INTERFACE_PRIMITIVE_TYPE = 'PHPFHIRPrimitiveTypeInterface';
@@ -98,8 +97,7 @@
 const PHPFHIR_TRAIT_COMMENT_CONTAINER = 'PHPFHIRCommentContainerTrait';
 const PHPFHIR_TRAIT_VALIDATION_ASSERTIONS = 'PHPFHIRValidationAssertionsTrait';
 const PHPFHIR_TRAIT_CHANGE_TRACKING = 'PHPFHIRChangeTrackingTrait';
-const PHPFHIR_TRAIT_XMLNS = 'PHPFHIRXmlNamespaceTrait';
-const PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG = 'PHPFHIRXmlSerializableConfigTrait';
+const PHPFHIR_TRAIT_SOURCE_XMLNS = 'PHPFHIRSourceXmlNamespaceTrait';
 
 // Core enums
 const PHPFHIR_ENUM_CONFIG_KEY = 'PHPFHIRConfigKeyEnum';
diff --git a/src/Builder.php b/src/Builder.php
index 13ea0335..762c0422 100644
--- a/src/Builder.php
+++ b/src/Builder.php
@@ -241,14 +241,14 @@ protected function writeCoreTypeFiles(): void
             $suffix = ucfirst($ftype);
 
             // define "default" namespace
-            $ns = $this->config->getNamespace(true);
+            $ns = $this->config->getFullyQualifiedName(true);
 
             if ('class' === $ftype) {
                 // 'class' types do have suffix
                 $suffix = '';
             } else if ('test' === $ftype) {
                 // test classes have different namespace
-                $ns = $this->config->getTestsNamespace(TestType::BASE, true);
+                $ns = $this->config->getFullyQualifiedTestsName(TestType::BASE, true);
                 // trim subtype
                 $fname = substr($fname, strpos($fname, '_') + 1);
             }
diff --git a/src/Config/VersionConfig.php b/src/Config/VersionConfig.php
index 692ed0f2..3bba9146 100644
--- a/src/Config/VersionConfig.php
+++ b/src/Config/VersionConfig.php
@@ -78,11 +78,17 @@ public function getUrl(): string
 
     /**
      * @param bool $leadingSlash
+     * @param string ...$bits
      * @return string
      */
-    public function getNamespace(bool $leadingSlash): string
+    public function getFullyQualifiedName(bool $leadingSlash, string... $bits): string
     {
-        return $this->version->getNamespace($leadingSlash);
+        $ns = $this->version->getNamespace($leadingSlash);
+        $bits = array_filter($bits);
+        if ([] === $bits) {
+            return $ns;
+        }
+        return sprintf('%s\\%s', $ns, implode('\\' , $bits));
     }
 
     /**
@@ -104,18 +110,12 @@ public function getLibxmlOpts(): ?int
     /**
      * @param \DCarbone\PHPFHIR\Enum\TestType $testType
      * @param bool $leadingSlash
+     * @param string ...$bits
      * @return string
      */
-    public function getTestsNamespace(TestType $testType, bool $leadingSlash): string
+    public function getFullyQualifiedTestsName(TestType $testType, bool $leadingSlash, string... $bits): string
     {
-        $ns = $this->getNamespace(false);
-
-        if ('' === $ns) {
-            $ns = $testType->namespaceSlug();
-        } else {
-            $ns .= '\\' . $testType->namespaceSlug();
-        }
-        return $leadingSlash ? "\\{$ns}" : $ns;
+        return $this->getFullyQualifiedName($leadingSlash, $testType->namespaceSlug(), ...$bits);
     }
 
     /**
diff --git a/src/Definition.php b/src/Definition.php
index 168b6752..856a4e7d 100644
--- a/src/Definition.php
+++ b/src/Definition.php
@@ -84,9 +84,6 @@ public function buildDefinition(): void
         $log->info('Finding property types');
         TypePropertyDecorator::findPropertyTypes($this->config, $this->types);
 
-        $log->info('Ensuring primitive type children have "value" property');
-        TypeDecorator::ensureValueOnPrimitiveChildTypes($this->config, $this->types);
-
         $log->info('Finding overloaded properties in child types');
         TypePropertyDecorator::findOverloadedProperties($this->config, $this->types);
 
diff --git a/src/Definition/Type.php b/src/Definition/Type.php
index 2b20a5e6..088c193b 100644
--- a/src/Definition/Type.php
+++ b/src/Definition/Type.php
@@ -273,15 +273,7 @@ public function getClassName(): string
      */
     public function getFullyQualifiedNamespace(bool $leadingSlash): string
     {
-        $ns = $this->getConfig()->getNamespace(false);
-        $typeNS = $this->getTypeNamespace();
-        if ('' !== $typeNS) {
-            $ns = sprintf('%s\\%s', $ns, $typeNS);
-        }
-        return match ($leadingSlash) {
-            true => sprintf('\\%s', $ns),
-            false => $ns,
-        };
+        return $this->getConfig()->getFullyQualifiedName($leadingSlash, $this->getTypeNamespace());
     }
 
     /**
@@ -291,15 +283,7 @@ public function getFullyQualifiedNamespace(bool $leadingSlash): string
      */
     public function getFullyQualifiedTestNamespace(TestType $testType, bool $leadingSlash): string
     {
-        $ns = $this->getConfig()->getTestsNamespace($testType, false);
-        $typeNS = $this->getTypeNamespace();
-        if ('' !== $typeNS) {
-            $ns = sprintf('%s\\%s', $ns, $typeNS);
-        }
-        return match ($leadingSlash) {
-            true => sprintf('\\%s', $ns),
-            false => $ns,
-        };
+        return $this->getConfig()->getFullyQualifiedTestsName($testType, $leadingSlash,$this->getTypeNamespace());
     }
 
     /**
@@ -308,16 +292,7 @@ public function getFullyQualifiedTestNamespace(TestType $testType, bool $leading
      */
     public function getFullyQualifiedClassName(bool $leadingSlash): string
     {
-        $cn = $this->getFullyQualifiedNamespace(false);
-        if ('' === $cn) {
-            $cn = $this->getClassName();
-        } else {
-            $cn = sprintf('%s\\%s', $cn, $this->getClassName());
-        }
-        return match ($leadingSlash) {
-            true => sprintf('\\%s', $cn),
-            false => $cn,
-        };
+        return $this->getConfig()->getFullyQualifiedName($leadingSlash, $this->getTypeNamespace(), $this->getClassName());
     }
 
     /**
@@ -335,16 +310,7 @@ public function getTestClassName(): string
      */
     public function getFullyQualifiedTestClassName($testType, bool $leadingSlash): string
     {
-        $cn = $this->getFullyQualifiedTestNamespace($testType, false);
-        if ('' === $cn) {
-            $cn = $this->getTestClassName();
-        } else {
-            $cn = sprintf('%s\\%s', $cn, $this->getTestClassName());
-        }
-        return match ($leadingSlash) {
-            true => sprintf('\\%s', $cn),
-            false => $cn,
-        };
+        return $this->getConfig()->getFullyQualifiedTestsName($testType, $leadingSlash, $this->getTypeNamespace(), $this->getTestClassName());
     }
 
     /**
@@ -789,7 +755,7 @@ public function getDirectlyUsedTraits(): array
                     $traits,
                     PHPFHIR_TRAIT_VALIDATION_ASSERTIONS,
                     PHPFHIR_TRAIT_CHANGE_TRACKING,
-                    PHPFHIR_TRAIT_XMLNS,
+                    PHPFHIR_TRAIT_SOURCE_XMLNS,
                 );
             }
         } else if (!$parentType->hasLocalProperties()) {
@@ -799,7 +765,7 @@ public function getDirectlyUsedTraits(): array
                 $traits,
                 PHPFHIR_TRAIT_VALIDATION_ASSERTIONS,
                 PHPFHIR_TRAIT_CHANGE_TRACKING,
-                PHPFHIR_TRAIT_XMLNS,
+                PHPFHIR_TRAIT_SOURCE_XMLNS,
             );
         }
 
diff --git a/src/Definition/TypeDecorator.php b/src/Definition/TypeDecorator.php
index f4e2c7f7..243e0ab9 100644
--- a/src/Definition/TypeDecorator.php
+++ b/src/Definition/TypeDecorator.php
@@ -204,32 +204,6 @@ public static function determinePrimitiveTypes(VersionConfig $config, Types $typ
         }
     }
 
-    /**
-     * @param \DCarbone\PHPFHIR\Config\VersionConfig $config
-     * @param \DCarbone\PHPFHIR\Definition\Types $types
-     */
-    public static function ensureValueOnPrimitiveChildTypes(VersionConfig $config, Types $types): void
-    {
-        $logger = $config->getLogger();
-        foreach ($types->getIterator() as $type) {
-            if (!$type->hasPrimitiveParent() ||
-                null !== $type->getLocalProperties()->getProperty(PHPFHIR_VALUE_PROPERTY_NAME)) {
-                continue;
-            }
-            $logger->warning(
-                sprintf(
-                    'Type "%s" extends primitive "%s" but is missing "%s" property.  Adding...',
-                    $type->getFHIRName(),
-                    $type->getParentType()->getFHIRName(),
-                    PHPFHIR_VALUE_PROPERTY_NAME
-                )
-            );
-            $property = new Property($type, $type->getSourceSXE(), $type->getSourceFilename());
-            $property->setName(PHPFHIR_VALUE_PROPERTY_NAME);
-            $type->getLocalProperties()->addProperty($property);
-        }
-    }
-
     /**
      * @param \DCarbone\PHPFHIR\Config\VersionConfig $config
      * @param \DCarbone\PHPFHIR\Definition\Types $types
diff --git a/src/Definition/TypeImports.php b/src/Definition/TypeImports.php
index 0bd9ba63..af876d2a 100644
--- a/src/Definition/TypeImports.php
+++ b/src/Definition/TypeImports.php
@@ -221,15 +221,15 @@ private function buildImports(): void
         $this->addImport($this->type->getClassName(), $this->type->getFullyQualifiedNamespace(false));
 
         $typeNS = $this->type->getFullyQualifiedNamespace(false);
-        $configNS = $this->type->getConfig()->getNamespace(false);
+        $configNS = $this->type->getConfig()->getFullyQualifiedName(false);
 
         $sortedProperties = $this->type->getAllPropertiesIterator();
 
-        // always add xml serializable interface and root config to all non-abstract types
+        // non-abstract types must import config and xml writer
         if (!$this->type->isAbstract()) {
             $this->addImport(PHPFHIR_CLASSNAME_CONFIG, $configNS);
-            $this->addImport(PHPFHIR_INTERFACE_XML_SERIALIZABLE, $configNS);
-            $this->addImport(PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG, $configNS);
+            $this->addImport(PHPFHIR_CLASSNAME_XML_WRITER, $configNS);
+            $this->addImport(PHPFHIR_ENUM_CONFIG_KEY, $configNS);
         }
 
         // if this type is in a nested namespace, there are  a few base interfaces, classes, and traits
diff --git a/src/Utilities/FileUtils.php b/src/Utilities/FileUtils.php
index f3a786c8..f14efc64 100644
--- a/src/Utilities/FileUtils.php
+++ b/src/Utilities/FileUtils.php
@@ -108,7 +108,7 @@ public static function buildAutoloaderRelativeFilepath(VersionConfig $config, Ty
     {
         return ltrim(
                 str_replace(
-                    [$config->getNamespace(false), '\\'],
+                    [$config->getFullyQualifiedName(false), '\\'],
                     ['', '/'],
                     $type->getFullyQualifiedClassName(false)
                 ),
diff --git a/src/Utilities/TypeHintUtils.php b/src/Utilities/TypeHintUtils.php
index 4aaa743e..7a52f546 100644
--- a/src/Utilities/TypeHintUtils.php
+++ b/src/Utilities/TypeHintUtils.php
@@ -174,7 +174,7 @@ public static function typeTypeDoc(VersionConfig $config, Type $type, bool $null
         if ($tk->isOneOf(TypeKind::RESOURCE_INLINE, TypeKind::RESOURCE_CONTAINER)) {
             array_push(
                 $types,
-                sprintf('\\%s\\', trim($config->getNamespace(true), '\\')),
+                sprintf('\\%s\\', trim($config->getFullyQualifiedName(true), '\\')),
                 PHPFHIR_INTERFACE_CONTAINED_TYPE,
             );
         } else {
diff --git a/template/core/classes/class_autoloader.php b/template/core/classes/class_autoloader.php
index 79cda867..76edf0ef 100644
--- a/template/core/classes/class_autoloader.php
+++ b/template/core/classes/class_autoloader.php
@@ -22,8 +22,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
-$nsPrefix = "{$namespace}\\";
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -38,71 +37,73 @@
 echo "\n\n"; ?>
 // if this class is used, assume not using Composer...
 
+// constants
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONSTANTS); ?>', false)) {
+    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>.php';
+}
+
+// config
+if (!enum_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_ENUM_CONFIG_KEY); ?>', false)) {
+    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>.php';
+}
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?>', false)) {
+    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_CONFIG; ?>.php';
+}
+
+// xml writer
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?>', false)) {
+    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>.php';
+}
+
 // interfaces
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_TYPE; ?>', false)) {
+if (!interface_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_INTERFACE_TYPE); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_TYPE; ?>.php';
 }
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_PRIMITIVE_TYPE; ?>', false)) {
+if (!interface_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_INTERFACE_PRIMITIVE_TYPE); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_PRIMITIVE_TYPE; ?>.php';
 }
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>', false)) {
+if (!interface_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_INTERFACE_CONTAINED_TYPE); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>.php';
 }
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_COMMENT_CONTAINER; ?>', false)) {
+if (!interface_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_INTERFACE_COMMENT_CONTAINER); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_COMMENT_CONTAINER; ?>.php';
 }
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>.php';
-}
-if (!interface_exists('\<?php echo $nsPrefix . PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?>.php';
-}
 
 // traits
-if (!trait_exists('\<?php echo $nsPrefix . PHPFHIR_TRAIT_COMMENT_CONTAINER; ?>', false)) {
+if (!trait_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_TRAIT_COMMENT_CONTAINER); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_COMMENT_CONTAINER; ?>.php';
 }
-if (!trait_exists('\<?php echo $nsPrefix . PHPFHIR_TRAIT_VALIDATION_ASSERTIONS; ?>', false)) {
+if (!trait_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_TRAIT_VALIDATION_ASSERTIONS); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_VALIDATION_ASSERTIONS; ?>.php';
 }
-if (!trait_exists('\<?php echo $nsPrefix . PHPFHIR_TRAIT_CHANGE_TRACKING; ?>', false)) {
+if (!trait_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_TRAIT_CHANGE_TRACKING); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_CHANGE_TRACKING; ?>.php';
 }
-if (!trait_exists('\<?php echo $nsPrefix . PHPFHIR_TRAIT_XMLNS; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_XMLNS; ?>.php';
-}
-if (!trait_exists('\<?php echo $nsPrefix . PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG; ?>.php';
+if (!trait_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_TRAIT_SOURCE_XMLNS); ?>', false)) {
+    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_TRAIT_SOURCE_XMLNS; ?>.php';
 }
 
 // enums
-if (!enum_exists('\<?php echo $nsPrefix . PHPFHIR_ENUM_CONFIG_KEY; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>.php';
-}
-if (!enum_exists('\<?php echo $nsPrefix . PHPFHIR_ENUM_TYPE; ?>', false)) {
+if (!enum_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_ENUM_TYPE); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_ENUM_TYPE; ?>.php';
 }
-if (!enum_exists('\<?php echo $nsPrefix . PHPFHIR_ENUM_API_FORMAT; ?>', false)) {
+if (!enum_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_ENUM_API_FORMAT); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_ENUM_API_FORMAT; ?>.php';
 }
 
-// classes
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_CONSTANTS; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>.php';
-}
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_TYPEMAP; ?>', false)) {
+// parser classes
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_TYPEMAP); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_TYPEMAP; ?>.php';
 }
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_CONFIG; ?>', false)) {
-    require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_CONFIG; ?>.php';
-}
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_RESPONSE_PARSER; ?>', false)) {
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_RESPONSE_PARSER); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_RESPONSE_PARSER; ?>.php';
 }
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_DEBUG_CLIENT_RESPONSE; ?>', false)) {
+
+// debug client
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_DEBUG_CLIENT_RESPONSE); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT_RESPONSE; ?>.php';
 }
-if (!class_exists('\<?php echo $nsPrefix . PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?>', false)) {
+if (!class_exists('<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_DEBUG_CLIENT); ?>', false)) {
     require __DIR__ . DIRECTORY_SEPARATOR . '<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?>.php';
 }
 
diff --git a/template/core/classes/class_config.php b/template/core/classes/class_config.php
index 642c89ae..90c49a8d 100644
--- a/template/core/classes/class_config.php
+++ b/template/core/classes/class_config.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -41,13 +41,20 @@
 <?php endif; ?>
 
  */
-class <?php echo PHPFHIR_CLASSNAME_CONFIG; ?> implements <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>, \JsonSerializable
+class <?php echo PHPFHIR_CLASSNAME_CONFIG; ?> implements \JsonSerializable
 {
-    use <?php echo PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG; ?>;
-
     /** @var bool */
     private bool $registerAutoloader = false;
 
+    /** @var int */
+    private int $libxmlOpts;
+
+    /** @var string */
+    private string $rootXmlns;
+
+    /** @var bool */
+    private bool $overrideSourceXmlns;
+
     /**
      * <?php echo PHPFHIR_CLASSNAME_CONFIG; ?> Constructor
      * @param array $config
@@ -64,7 +71,7 @@ public function __construct(array $config = [])
     /**
      * Set arbitrary key on this config
      *
-     * @param \<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_ENUM_CONFIG_KEY; ?>|string $key
+     * @param <?php echo $config->getFullyQualifiedName(true, PHPFHIR_ENUM_CONFIG_KEY); ?>|string $key
      * @param mixed $value
      * @return static
      */
@@ -95,14 +102,76 @@ public function getRegisterAutoloader(): bool
         return $this->registerAutoloader;
     }
 
+    /**
+     * Sets the option flags to provide to libxml when unserializing XML
+     *
+     * @param int $libxmlOpts
+     * @return static
+     */
+    public function setLibxmlOpts(int $libxmlOpts): self
+    {
+        $this->libxmlOpts = $libxmlOpts;
+        return $this;
+    }
+
+    /**
+     * Returns set libxml option flags
+     *
+     * @return int
+     */
+    public function getLibxmlOpts(): int
+    {
+        return $this->libxmlOpts ?? <?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>::DEFAULT_LIBXML_OPTS;
+    }
+
+    /**
+     * Default root xmlns to use.
+     *
+     * @param string $rootXmlns
+     * @return static
+     */
+    public function setRootXmlns(string $rootXmlns): self
+    {
+        $this->rootXmlns = $rootXmlns;
+        return $this;
+    }
+
+    /**
+     * @return null|string
+     */
+    public function getRootXmlns(): null|string
+    {
+        return $this->rootXmlns ?? null;
+    }
+
+    /**
+     * If true, overrides the xmlns entry found at the root of a source document, if there was one.
+     *
+     * @param bool $overrideSourceXmlns
+     * @return static
+     */
+    public function setOverrideSourceXmlns(bool $overrideSourceXmlns): self
+    {
+        $this->overrideSourceXmlns = $overrideSourceXmlns;
+        return $this;
+    }
+
+    /**
+     * @return bool
+     */
+    public function getOverrideSourceXmlns(): bool
+    {
+        return $this->overrideSourceXmlns ?? false;
+    }
+
     /**
      * @return \stdClass
      */
     public function jsonSerialize(): \stdClass
     {
         $out = new \stdClass();
-        foreach(<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::values() as $k => $_) {
-            $out->{$k} = $this->{'get'.$k}();
+        foreach(<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::cases() as $key) {
+            $out->{$k} = $this->{$key->getter()}();
         }
         return $out;
     }
diff --git a/template/core/classes/class_constants.php b/template/core/classes/class_constants.php
index 4fb976e3..d23f447e 100644
--- a/template/core/classes/class_constants.php
+++ b/template/core/classes/class_constants.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -42,7 +42,7 @@
 <?php endif; ?>
 
  */
-abstract class <?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>
+final class <?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>
 
 {
     // FHIR source
@@ -52,6 +52,10 @@ abstract class <?php echo PHPFHIR_CLASSNAME_CONSTANTS; ?>
     // PHPFHIR
     public const CODE_GENERATION_DATE = '<?php echo CopyrightUtils::getStandardDate(); ?>';
 
+    // Config Defaults
+    public const DEFAULT_LIBXML_OPTS = LIBXML_NONET | LIBXML_BIGLINES | LIBXML_PARSEHUGE | LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD | LIBXML_NOXMLDECL;
+    public const DEFAULT_XMLNS = 'https://hl7.org/fhir';
+
     // Common
     public const JSON_FIELD_RESOURCE_TYPE = 'resourceType';
     public const JSON_FIELD_FHIR_COMMENTS = 'fhir_comments';
diff --git a/template/core/classes/class_debug_client.php b/template/core/classes/class_debug_client.php
index 2de007d9..64cc3dff 100644
--- a/template/core/classes/class_debug_client.php
+++ b/template/core/classes/class_debug_client.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -72,6 +72,22 @@ public function __construct(string $baseUrl, array $curlOpts = [], )
         $this->_curlOpts = $curlOpts;
     }
 
+    /**
+     * @return string
+     */
+    public function _getBaseUrl(): string
+    {
+        return $this->_baseUrl;
+    }
+
+    /**
+     * @return array
+     */
+    public function _getBaseCurlOpts(): array
+    {
+        return $this->_curlOpts;
+    }
+
     /**
      * @param string $path
      * @param array $queryParams
diff --git a/template/core/classes/class_debug_client_response.php b/template/core/classes/class_debug_client_response.php
index 85ebe446..58bfed0e 100644
--- a/template/core/classes/class_debug_client_response.php
+++ b/template/core/classes/class_debug_client_response.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
diff --git a/template/core/classes/class_response_parser.php b/template/core/classes/class_response_parser.php
index 1d3a0e2b..85a739b5 100644
--- a/template/core/classes/class_response_parser.php
+++ b/template/core/classes/class_response_parser.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -143,7 +143,18 @@ public function parseStdClass(\stdClass $input): null|<?php echo PHPFHIR_INTERFA
     public function parseSimpleXMLElement(\SimpleXMLElement $input): null|<?php echo PHPFHIR_INTERFACE_TYPE; ?>
 
     {
-        return $this->parseDOMDocument(dom_import_simplexml($input)->ownerDocument);
+        $elementName = $input->getName();
+        $className = <?php echo PHPFHIR_CLASSNAME_TYPEMAP; ?>::getTypeClass($elementName);
+        /** @var \<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_TYPE; ?> $fhirType */
+        $fhirType = <?php echo PHPFHIR_CLASSNAME_TYPEMAP; ?>::getTypeClass($elementName);
+        if (null === $fhirType) {
+            throw new \UnexpectedValueException(sprintf(
+                'Unable to locate FHIR type for root XML element "%s". Input seen: %s',
+                $elementName,
+                $this->getPrintableStringInput($input->saveXML())
+            ));
+        }
+        return $fhirType::xmlUnserialize($input, $this->config);
     }
 
     /**
@@ -154,17 +165,7 @@ public function parseSimpleXMLElement(\SimpleXMLElement $input): null|<?php echo
     public function parseDOMDocument(\DOMDocument $input): null|<?php echo PHPFHIR_INTERFACE_TYPE; ?>
 
     {
-        $elementName = $input->documentElement->nodeName;
-        /** @var \<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_TYPE; ?> $fhirType */
-        $fhirType = <?php echo PHPFHIR_CLASSNAME_TYPEMAP; ?>::getTypeClass($elementName);
-        if (null === $fhirType) {
-            throw new \UnexpectedValueException(sprintf(
-                'Unable to locate FHIR type for root XML element "%s". Input seen: %s',
-                $elementName,
-                $this->getPrintableStringInput($input->saveXML())
-            ));
-        }
-        return $fhirType::xmlUnserialize($input->documentElement, $this->config);
+        return $this->parseSimpleXMLElement(simplexml_import_dom($input));
     }
 
     /**
@@ -193,12 +194,11 @@ public function parseXml(string $input): null|<?php echo PHPFHIR_INTERFACE_TYPE;
 
     {
         libxml_use_internal_errors(true);
-        $dom = $this->config->newDOMDocment();
-        $dom->loadXML($input, $this->config->getLibxmlOpts());
+        $sxe = new \SimpleXMLElement($input, $this->config->getLibxmlOpts();
         $err = libxml_get_last_error();
         libxml_use_internal_errors(false);
         if (false === $err) {
-            return $this->parseDOMDocument($dom);
+            return $this->parseSimpleXMLElement($dom);
         }
         throw new \DomainException(sprintf(
             'Unable to parse provided input as XML.  Error: %s; Input: %s',
diff --git a/template/core/classes/class_type_map.php b/template/core/classes/class_type_map.php
index 5782187b..a62055d2 100644
--- a/template/core/classes/class_type_map.php
+++ b/template/core/classes/class_type_map.php
@@ -22,7 +22,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 $containerType = $types->getContainerType($config->getVersion()->getName());
 if (null === $containerType) {
@@ -121,18 +121,18 @@ public static function getContainedTypeClassName(string $typeName): null|string
 
     /**
      * Will attempt to determine if the provided value is or describes a containable resource type
-     * @param string|array|\DOMElement|<?php echo PHPFHIR_INTERFACE_TYPE; ?> $type
+     * @param string|array|\SimpleXMLElement|<?php echo PHPFHIR_INTERFACE_TYPE; ?> $type
      * @return bool
      * @throws \InvalidArgumentException
      */
-    public static function isContainableResource(string|array|\DOMElement|<?php echo PHPFHIR_INTERFACE_TYPE; ?> $type): bool
+    public static function isContainableResource(string|array|\SimpleXMLElement|<?php echo PHPFHIR_INTERFACE_TYPE; ?> $type): bool
     {
         $tt = gettype($type);
         if ('object' === $tt) {
             if ($type instanceof <?php echo PHPFHIR_INTERFACE_TYPE; ?>) {
                 return in_array('\\' . get_class($type), self::CONTAINABLE_TYPES, true);
             }
-            return isset(self::CONTAINABLE_TYPES[$type->nodeName]);
+            return isset(self::CONTAINABLE_TYPES[$type->getName()]);
         }
         if ('string' === $tt) {
             return isset(self::CONTAINABLE_TYPES[$type]) || in_array('\\' . ltrim($type, '\\'), self::CONTAINABLE_TYPES, true);
@@ -144,26 +144,29 @@ public static function isContainableResource(string|array|\DOMElement|<?php echo
     }
 
     /**
-     * @param \DOMElement $node Parent element containing inline resource
-     * @return \<?php echo ('' !== $namespace ? "{$namespace}\\" : '') . PHPFHIR_INTERFACE_CONTAINED_TYPE ?>|null
+     * @param \SimpleXMLElement $node Parent element containing inline resource
+     * @param <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config
+     * @return null|<?php echo $config->getfullyQualifiedName(true, PHPFHIR_INTERFACE_CONTAINED_TYPE); ?>
+
      */
-    public static function getContainedTypeFromXML(\DOMElement $node): ?<?php echo PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>
+    public static function getContainedTypeFromXML(\SimpleXMLElement $node, <?php echo PHPFHIR_CLASSNAME_CONFIG; ?> $config): null|<?php echo PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>
 
     {
-        $typeName = $node->nodeName;
+        $typeName = $node->getName();
         $className = self::getContainedTypeClassName($typeName);
         if (null === $className) {
             throw self::createdInvalidContainedTypeException($typeName);
         }
         /** @var \<?php echo ('' !== $namespace ? "{$namespace}\\" : '') . PHPFHIR_INTERFACE_CONTAINED_TYPE ?> $className */
-        return $className::xmlUnserialize($node);
+        return $className::xmlUnserialize($node, null, $config);
     }
 
     /**
      * @param array|null $data
-     * @return \<?php echo ('' !== $namespace ? "{$namespace}\\" : '') . PHPFHIR_INTERFACE_CONTAINED_TYPE ?>|null
+     * @return null|<?php echo $config->getfullyQualifiedName(true, PHPFHIR_INTERFACE_CONTAINED_TYPE); ?>
+
      */
-    public static function getContainedTypeFromArray(null|array $data): ?<?php echo PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>
+    public static function getContainedTypeFromArray(null|array $data): null|<?php echo PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>
 
     {
         if (null === $data || [] === $data) {
diff --git a/template/core/classes/class_xml_writer.php b/template/core/classes/class_xml_writer.php
new file mode 100644
index 00000000..2384765c
--- /dev/null
+++ b/template/core/classes/class_xml_writer.php
@@ -0,0 +1,172 @@
+<?php declare(strict_types=1);
+
+/*
+ * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
+
+/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
+/** @var \DCarbone\PHPFHIR\Definition\Types $types */
+
+$namespace = $config->getFullyQualifiedName(false);
+
+ob_start();
+
+echo "<?php declare(strict_types=1);\n\n";
+
+if ('' !== $namespace) :
+    echo "namespace {$namespace};\n\n";
+endif;
+
+echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
+
+echo "\n\n"; ?>
+/**
+ * Fhir Xml Writer
+ *
+ * Class <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?><?php if ('' !== $namespace) : ?>
+
+ * @package \<?php echo $namespace; ?>
+<?php endif; ?>
+
+ */
+class <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?> extends \XMLWriter
+{
+    private const MEM = 'memory';
+
+    /** @var bool */
+    private bool $_docStarted = false;
+    /** @var bool */
+    private bool $_rootOpen = false;
+    /** @var null|string */
+    private null|string $_open = null;
+
+    /**
+     * @see https://www.php.net/manual/en/xmlwriter.openmemory.php
+     *
+     * @return bool
+     */
+    public function openMemory(): bool
+    {
+        $this->_open = self::MEM;
+        return parent::openMemory();
+    }
+
+    /**
+     * @see https://www.php.net/manual/en/xmlwriter.openuri.php
+     *
+     * @param string $uri
+     * @return bool
+     */
+    public function openUri(string $uri): bool
+    {
+        $this->_open = $uri;
+        return parent::openUri($uri);
+    }
+
+    /**
+     * @return bool
+     */
+    public function isOpen(): bool
+    {
+        return null !== $this->_open;
+    }
+
+    /**
+     * Returns the destination of writes made by this class.  Value will be "null" if not opened, "memory" if writing
+     * opened with "openMemory()", or the $uri provided to "openUri()"
+     *
+     * @return null|string
+     */
+    public function getWriteDestination(): null|string
+    {
+        return $this->_open;
+    }
+
+    /**
+     * Used to track whether the document has been started
+     *
+     * @return bool
+     */
+    public function isDocStarted(): bool
+    {
+        return $this->_docStarted;
+    }
+
+    /**
+     * @see https://www.php.net/manual/en/xmlwriter.startdocument.php
+     *
+     * @param null|string $version
+     * @param null|string $encoding
+     * @param null|string $standalone
+     * @return bool
+     */
+    public function startDocument(null|string $version = '1.0', null|string $encoding = 'UTF-8', null|string $standalone = 'yes'): bool
+    {
+        $this->_docStarted = true;
+        return parent::startDocument($version, $encoding, $standalone);
+    }
+
+    /**
+     * @see https://www.php.net/manual/en/xmlwriter.startattribute.php
+     *
+     * @param string $name Attribute name
+     * @param string $value Attribute value
+     * @return bool
+     */
+    public function writeAttribute(string $name, string $value): bool
+    {
+        return $this->startAttribute($name)
+            && $this->text($value)
+            && $this->endAttribute();
+    }
+
+    /**
+     * @return bool
+     */
+    public function isRootOpen(): bool
+    {
+        return $this->_rootOpen;
+    }
+
+    /**
+     * @param <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config
+     * @param string $name
+     * @param string|null $sourceXmlns
+     * @return bool
+     */
+    public function openRootNode(<?php echo PHPFHIR_CLASSNAME_CONFIG; ?> $config, string $name, null|string $sourceXmlns): bool
+    {
+        $ok = $this->startElement($name);
+        if (!$ok) {
+            return false;
+        }
+        if ($config->getOverrideSourceXmlns() || null === $sourceXmlns) {
+            $ns = (string)$config->getRootXmlns();
+        } else {
+            $ns = $sourceXmlns;
+        }
+        if ('' !== $ns) {
+            $ok = $this->writeAttribute('xmlns', $ns);
+            if (!$ok) {
+                return false;
+            }
+        }
+        $this->_rootOpen = true;
+        return true;
+    }
+}
+<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/core/enums/enum_api_format.php b/template/core/enums/enum_api_format.php
index 15865bc9..4f443125 100644
--- a/template/core/enums/enum_api_format.php
+++ b/template/core/enums/enum_api_format.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
diff --git a/template/core/enums/enum_config_key.php b/template/core/enums/enum_config_key.php
index 04e5884b..057f1ae5 100644
--- a/template/core/enums/enum_config_key.php
+++ b/template/core/enums/enum_config_key.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -45,10 +45,24 @@ enum <?php echo PHPFHIR_ENUM_CONFIG_KEY; ?> : string
 {
     case REGISTER_AUTOLOADER = 'registerAutoloader';
     case LIBXML_OPTS = 'libxmlOpts';
-    case DOM_VERSION = 'domVersion';
-    case XML_ENCODING = 'encoding';
-    case PRESERVE_WHITESPACE = 'preserveWhitespace';
-    case FORMAT_OUTPUT = 'formatOutput';
+    case ROOT_XMLNS = 'rootXmlns';
+    case OVERRIDE_SOURCE_XMLNS = 'overrideSourceXmlns';
+
+    /**
+     * @return string
+     */
+    public function setter(): string
+    {
+        return 'set' . $this->value;
+    }
+
+    /**
+     * @return string
+     */
+    public function getter(): string
+    {
+        return 'get' . $this->value;
+    }
 
     /**
      * @return array
diff --git a/template/core/enums/enum_type.php b/template/core/enums/enum_type.php
index 35fa0804..4eea013c 100644
--- a/template/core/enums/enum_type.php
+++ b/template/core/enums/enum_type.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
diff --git a/template/core/interfaces/interface_comment_container.php b/template/core/interfaces/interface_comment_container.php
index 05ffc39a..031980e3 100644
--- a/template/core/interfaces/interface_comment_container.php
+++ b/template/core/interfaces/interface_comment_container.php
@@ -20,7 +20,7 @@
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
diff --git a/template/core/interfaces/interface_contained_type.php b/template/core/interfaces/interface_contained_type.php
index 01786b2c..67ff7d04 100644
--- a/template/core/interfaces/interface_contained_type.php
+++ b/template/core/interfaces/interface_contained_type.php
@@ -22,7 +22,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 $containerType = $types->getContainerType($config->getVersion()->getName());
 if (null === $containerType) {
diff --git a/template/core/interfaces/interface_primitive_type.php b/template/core/interfaces/interface_primitive_type.php
index 0ff59992..8f748eff 100644
--- a/template/core/interfaces/interface_primitive_type.php
+++ b/template/core/interfaces/interface_primitive_type.php
@@ -21,7 +21,7 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
diff --git a/template/core/interfaces/interface_type.php b/template/core/interfaces/interface_type.php
index 904198d8..71c1195c 100644
--- a/template/core/interfaces/interface_type.php
+++ b/template/core/interfaces/interface_type.php
@@ -20,7 +20,7 @@
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 
 ob_start();
 
@@ -41,13 +41,21 @@
 <?php endif; ?>
 
  */
-interface <?php echo PHPFHIR_INTERFACE_TYPE; ?> extends <?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?>, \JsonSerializable
+interface <?php echo PHPFHIR_INTERFACE_TYPE; ?> extends \JsonSerializable
 {
     /**
      * Returns the FHIR name represented by this Type
      * @return string
      */
-    public function _getFHIRTypeName(): string;
+    public function _getFhirTypeName(): string;
+
+    /**
+     * Returns the root Xmlns value found in the source.  Null indicates no "xmlns" was found.  Only defined when
+     * unserializing XML, and only used when serializing XML.
+     *
+     * @return null|string
+     */
+    public function _getSourceXmlns(): null|string;
 
     /**
      * Must return an associative array in structure ["field" => ["rule" => {constraint}]] to be used during validation
@@ -68,6 +76,22 @@ public function _getValidationErrors(): array;
      */
     public function _isValued(): bool;
 
+    /**
+     * @param null|string|\SimpleXMLElement $element
+     * @param null|static $type
+     * @param null|int|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config PHP FHIR config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @return null|static
+     */
+    public static function xmlUnserialize(null|string|\SimpleXMLElement $element, <?php echo PHPFHIR_INTERFACE_TYPE; ?> $type = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): null|self;
+
+    /**
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?> $xw
+     * @param null|int|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config PHP FHIR config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @return <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?>
+
+     */
+    public function xmlSerialize(null|<?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?> $xw = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>;
+
     /**
      * @return string
      */
diff --git a/template/core/interfaces/interface_xml_serializable.php b/template/core/interfaces/interface_xml_serializable.php
deleted file mode 100644
index 8c68e693..00000000
--- a/template/core/interfaces/interface_xml_serializable.php
+++ /dev/null
@@ -1,83 +0,0 @@
-<?php declare(strict_types=1);
-
-/*
- * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
-
-/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
-
-$namespace = $config->getNamespace(false);
-
-ob_start();
-
-echo "<?php declare(strict_types=1);\n\n";
-
-if ('' !== $namespace) :
-    echo "namespace {$namespace};\n\n";
-endif;
-
-echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
-
-echo "\n\n";
-?>
-/**
- * Interface <?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; if ('' !== $namespace) : ?>
-
- * @package \<?php echo $namespace; ?>
-<?php endif; ?>
-
- */
-interface <?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?>
-
-{
-    /**
-     * Returns the xml namespace to use for this type when serializing to XML, if applicable.
-     * @return string
-     */
-    public function _getFHIRXMLNamespace(): string;
-
-    /**
-     * Set the XML Namespace to be output when serializing this type to XML
-     * @param string $xmlNamespace
-     * @return static
-     */
-    public function _setFHIRXMLNamespace(string $xmlNamespace): self;
-
-    /**
-     * Returns the base xml element definition for this type
-     *
-     * @param string $elementName Name of the root element
-     * @return string
-     */
-    public function _getFHIRXMLElementDefinition(string $elementName): string;
-
-    /**
-     * @param null|string|\DOMElement $element
-     * @param null|static $type
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
-     * @return null|static
-     */
-    public static function xmlUnserialize(null|string|\DOMElement $element, <?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?> $type = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): null|self;
-
-    /**
-     * @param null|\DOMElement $element
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
-     * @return \DOMElement
-     */
-    public function xmlSerialize(null|\DOMElement $element = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): \DOMElement;
-}
-<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/core/interfaces/interface_xml_serializable_config.php b/template/core/interfaces/interface_xml_serializable_config.php
deleted file mode 100644
index cba6d4f8..00000000
--- a/template/core/interfaces/interface_xml_serializable_config.php
+++ /dev/null
@@ -1,121 +0,0 @@
-<?php declare(strict_types=1);
-
-/*
- * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
-
-/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
-
-$namespace = $config->getNamespace(false);
-
-ob_start();
-
-echo "<?php declare(strict_types=1);\n\n";
-
-if ('' !== $namespace) :
-    echo "namespace {$namespace};\n\n";
-endif;
-
-echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
-
-echo "\n\n";
-?>
-/**
- * Interface <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; if ('' !== $namespace) : ?>
-
- * @package \<?php echo $namespace; ?>
-<?php endif; ?>
-
- */
-interface <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>
-
-{
-    public const DEFAULT_LIBXML_OPTS = LIBXML_NONET | LIBXML_PARSEHUGE | LIBXML_COMPACT;
-    public const DEFAULT_DOM_VERSION = '1.0';
-    public const DEFAULT_ENCODING = 'UTF-8';
-    public const DEFAULT_PRESERVE_WHITESPACE = true;
-    public const DEFAULT_FORMAT_OUTPUT = false;
-
-    /**
-     * Must construct a new \DOMDocument instance based on current configuration
-     *
-     * @return \DOMDocument
-     */
-    public function newDOMDocument(): \DOMDocument;
-
-    /**
-     * Sets the option flags to provide to libxml when serializing and unserializing XML
-     *
-     * @param int $libxmlOpts
-     * @return static
-     */
-    public function setLibxmlOpts(int $libxmlOpts): self;
-
-    /**
-     * Must return the set libxml option flags
-     *
-     * @return int
-     */
-    public function getLibxmlOpts(): int;
-
-    /**
-     * @param string $domVersion
-     * @return static
-     */
-    public function setDOMVersion(string $domVersion): self;
-
-    /**
-     * @return string
-     */
-    public function getDOMVersion(): string;
-
-    /**
-     * @param string $encoding
-     * @return static
-     */
-    public function setEncoding(string $encoding): self;
-
-    /**
-     * @return string
-     */
-    public function getEncoding(): string;
-
-    /**
-     * Sets whether or not to preserve whitespace when rendering XML
-     *
-     * @param bool $preserveWhitespace
-     * @return static
-     */
-    public function setPreserveWhitespace(bool $preserveWhitespace): self;
-
-    /**
-     * @return bool
-     */
-    public function getPreserveWhitespace(): bool;
-
-    /**
-     * @param bool $formatOutput
-     * @return static
-     */
-    public function setFormatOutput(bool $formatOutput): self;
-
-    /**
-     * @return bool
-     */
-    public function getFormatOutput(): bool;
-}
-<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/core/tests/test_class_constants.php b/template/core/tests/test_class_constants.php
index c39aab3b..86c11037 100644
--- a/template/core/tests/test_class_constants.php
+++ b/template/core/tests/test_class_constants.php
@@ -22,8 +22,8 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$rootNS = $config->getNamespace(false);
-$testNS = $config->getTestsNamespace(TestType::BASE, false);
+$rootNS = $config->getFullyQualifiedName(false);
+$testNS = $config->getFullyQualifiedTestsName(TestType::BASE, false);
 
 ob_start();
 echo "<?php\n\n";?>
diff --git a/template/core/tests/test_class_type_map.php b/template/core/tests/test_class_type_map.php
index cf978bdd..cb440c86 100644
--- a/template/core/tests/test_class_type_map.php
+++ b/template/core/tests/test_class_type_map.php
@@ -22,8 +22,8 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Types $types */
 
-$rootNS = $config->getNamespace(false);
-$testNS = $config->getTestsNamespace(TestType::BASE, false);
+$rootNS = $config->getFullyQualifiedName(false);
+$testNS = $config->getFullyQualifiedTestsName(TestType::BASE, false);
 
 ob_start();
 echo "<?php\n\n"; ?>
diff --git a/template/core/traits/trait_change_tracking.php b/template/core/traits/trait_change_tracking.php
index b7014cbd..8c8828d2 100644
--- a/template/core/traits/trait_change_tracking.php
+++ b/template/core/traits/trait_change_tracking.php
@@ -20,7 +20,7 @@
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 
-$rootNS = $config->getNamespace(false);
+$rootNS = $config->getFullyQualifiedName(false);
 
 ob_start();
 echo "<?php declare(strict_types=1);\n\n";
diff --git a/template/core/traits/trait_comment_container.php b/template/core/traits/trait_comment_container.php
index f42e0ba3..806c20be 100644
--- a/template/core/traits/trait_comment_container.php
+++ b/template/core/traits/trait_comment_container.php
@@ -20,7 +20,7 @@
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 
-$rootNS = $config->getNamespace(false);
+$rootNS = $config->getFullyQualifiedName(false);
 
 ob_start();
 echo "<?php declare(strict_types=1);\n\n";
diff --git a/template/core/traits/trait_source_xml_namespace.php b/template/core/traits/trait_source_xml_namespace.php
new file mode 100644
index 00000000..a826d057
--- /dev/null
+++ b/template/core/traits/trait_source_xml_namespace.php
@@ -0,0 +1,65 @@
+<?php declare(strict_types=1);
+
+/*
+ * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
+
+/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
+
+$rootNS = $config->getFullyQualifiedName(false);
+
+ob_start();
+echo "<?php declare(strict_types=1);\n\n";
+
+if ('' !== $rootNS) :
+    echo "namespace {$rootNS};\n\n";
+endif;
+
+echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
+
+echo "\n\n";
+?>
+/**
+ * Trait <?php echo PHPFHIR_TRAIT_SOURCE_XMLNS; if ('' !== $rootNS) : ?>
+
+ * @package \<?php echo $rootNS; ?>
+<?php endif; ?>
+
+ */
+trait <?php echo PHPFHIR_TRAIT_SOURCE_XMLNS; ?>
+
+{
+    /** @var string */
+    private string $_sourceXmlns;
+
+    /**
+     * @param string $xmlns
+     */
+    protected function _setSourceXmlns(string $xmlns): void
+    {
+        $this->_sourceXmlns = $xmlns;
+    }
+
+    /**
+     * @return null|string
+     */
+    public function _getSourceXmlns(): null|string
+    {
+        return $this->_sourceXmlns ?? null;
+    }
+}
+<?php return ob_get_clean();
diff --git a/template/core/traits/trait_validation_assertions.php b/template/core/traits/trait_validation_assertions.php
index 628a07f0..6b37fe6e 100644
--- a/template/core/traits/trait_validation_assertions.php
+++ b/template/core/traits/trait_validation_assertions.php
@@ -20,7 +20,7 @@
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 
-$rootNS = $config->getNamespace(false);
+$rootNS = $config->getFullyQualifiedName(false);
 
 ob_start();
 echo "<?php declare(strict_types=1);\n\n";
diff --git a/template/core/traits/trait_xml_namespace.php b/template/core/traits/trait_xml_namespace.php
deleted file mode 100644
index ac3f987f..00000000
--- a/template/core/traits/trait_xml_namespace.php
+++ /dev/null
@@ -1,85 +0,0 @@
-<?php declare(strict_types=1);
-
-/*
- * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
-
-/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
-
-$rootNS = $config->getNamespace(false);
-
-ob_start();
-echo "<?php declare(strict_types=1);\n\n";
-
-if ('' !== $rootNS) :
-    echo "namespace {$rootNS};\n\n";
-endif;
-
-echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
-
-echo "\n\n";
-?>
-    /**
-    * Trait <?php echo PHPFHIR_TRAIT_XMLNS; if ('' !== $rootNS) : ?>
-
-    * @package \<?php echo $rootNS; ?>
-<?php endif; ?>
-
-    */
-trait <?php echo PHPFHIR_TRAIT_XMLNS; ?>
-
-{
-    /** @var string */
-    protected string $_xmlns = '';
-
-    /**
-     * @param null|string $xmlNamespace
-     * @return static
-     */
-    public function _setFHIRXMLNamespace(null|string $xmlNamespace): self
-    {
-        $this->_xmlns = trim((string)$xmlNamespace);
-        return $this;
-    }
-
-    /**
-     * @return string
-     */
-    public function _getFHIRXMLNamespace(): string
-    {
-        return $this->_xmlns;
-    }
-
-    /**
-     * @param string $elementName Name to use for the element
-     * @return string
-     * @throws \InvalidArgumentException
-     */
-    public function _getFHIRXMLElementDefinition(string $elementName): string
-    {
-        if ('' === $elementName) {
-            throw new \InvalidArgumentException(sprintf('%s::_getFHIRXMLElementDefinition - $elementName is required', get_called_class()));
-        }
-        $xmlns = $this->_getFHIRXMLNamespace();
-        if ('' !==  $xmlns) {
-            $xmlns = sprintf(' xmlns="%s"', $xmlns);
-        }
-        return sprintf('<%1$s%2$s></%1$s>', $elementName, $xmlns);
-    }
-}
-
-<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/core/traits/trait_xml_serializable_config.php b/template/core/traits/trait_xml_serializable_config.php
deleted file mode 100644
index fbd8689f..00000000
--- a/template/core/traits/trait_xml_serializable_config.php
+++ /dev/null
@@ -1,164 +0,0 @@
-<?php declare(strict_types=1);
-
-/*
- * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-use DCarbone\PHPFHIR\Utilities\CopyrightUtils;
-
-/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
-
-$rootNS = $config->getNamespace(false);
-
-ob_start();
-echo "<?php declare(strict_types=1);\n\n";
-
-if ('' !== $rootNS) :
-    echo "namespace {$rootNS};\n\n";
-endif;
-
-echo CopyrightUtils::getFullPHPFHIRCopyrightComment();
-
-echo "\n\n";
-?>
-    /**
-    * Trait <?php echo PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG; if ('' !== $rootNS) : ?>
-
-    * @package \<?php echo $rootNS; ?>
-<?php endif; ?>
-
-    */
-trait <?php echo PHPFHIR_TRAIT_XML_SERIALIZABLE_CONFIG; ?>
-
-{
-    /** @var int */
-    private int $libxmlOpts;
-    /** @var string */
-    private string $domVersion;
-    /** @var string */
-    private string $encoding;
-    /** @var bool */
-    private bool $preserveWhitespace;
-    /** @var bool */
-    private bool $formatOutput;
-
-    /**
-     * @return \DOMDocument;
-     */
-    public function newDOMDocument(): \DOMDocument
-    {
-        $dom = new \DOMDocument($this->getDOMVersion(), $this->getEncoding());
-        $dom->preserveWhiteSpace = $this->getPreserveWhitespace();
-        $dom->formatOutput = $this->getFormatOutput();
-        return $dom;
-    }
-
-    /**
-     * Sets the option flags to provide to libxml when serializing and unserializing XML
-     *
-     * @param int $libxmlOpts
-     * @return static
-     */
-    public function setLibxmlOpts(int $libxmlOpts): self
-    {
-        $this->libxmlOpts = $libxmlOpts;
-        return $this;
-    }
-
-    /**
-     * Returns set libxml option flags
-     *
-     * @return int
-     */
-    public function getLibxmlOpts(): int
-    {
-        return $this->libxmlOpts ?? <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_LIBXML_OPTS;
-    }
-
-    /**
-     * @param string $domVersion
-     * @return static
-     */
-    public function setDOMVersion(string $domVersion): self
-    {
-        $this->domVersion = $domVersion;
-        return $this;
-    }
-
-    /**
-     * @return string
-     */
-    public function getDOMVersion(): string
-    {
-        return $this->domVersion ?? <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_DOM_VERSION;
-    }
-
-    /**
-     * @param string $encoding
-     * @return static
-     */
-    public function setEncoding(string $encoding): self
-    {
-        $this->encoding = $encoding;
-        return $this;
-    }
-
-    /**
-     * @return string
-     */
-    public function getEncoding(): string
-    {
-        return $this->encoding ?? <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_ENCODING;
-    }
-
-    /**
-     * Sets whether or not to preserve whitespace when rendering XML
-     *
-     * @param bool $preserveWhitespace
-     * @return static
-     */
-    public function setPreserveWhitespace(bool $preserveWhitespace): self
-    {
-        $this->preserveWhitespace = $preserveWhitespace;
-        return $this;
-    }
-
-    /**
-     * @return bool
-     */
-    public function getPreserveWhitespace(): bool
-    {
-        return $this->preserveWhitespace ?? <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_PRESERVE_WHITESPACE;
-    }
-
-    /**
-     * @param bool $formatOutput
-     * @return static
-     */
-    public function setFormatOutput(bool $formatOutput): self
-    {
-        $this->formatOutput = $formatOutput;
-        return $this;
-    }
-
-    /**
-     * @return bool
-     */
-    public function getFormatOutput(): bool
-    {
-        return $this->formatOutput ?? <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_FORMAT_OUTPUT;
-    }
-}
-<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/class_default.php b/template/types/class_default.php
index 1ad9e77f..f15bc1e4 100644
--- a/template/types/class_default.php
+++ b/template/types/class_default.php
@@ -16,7 +16,6 @@
  * limitations under the License.
  */
 
-use DCarbone\PHPFHIR\Enum\PrimitiveType;
 use DCarbone\PHPFHIR\Enum\TypeKind;
 
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
diff --git a/template/types/class_xhtml.php b/template/types/class_xhtml.php
index 3f9196c0..9d121005 100644
--- a/template/types/class_xhtml.php
+++ b/template/types/class_xhtml.php
@@ -52,71 +52,133 @@
  * @package <?php echo $fqns; ?>
 
  */
-class <?php echo $type->getClassName(); ?> implements <?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE ?>, \JsonSerializable
+class <?php echo $type->getClassName(); ?> implements <?php echo PHPFHIR_INTERFACE_TYPE ?>
+
 {
     use <?php echo PHPFHIR_TRAIT_CHANGE_TRACKING; ?>,
-        <?php echo PHPFHIR_TRAIT_XMLNS; ?>;
-
-    const _NOISE_NODES = ['html', 'head', 'body'];
+        <?php echo PHPFHIR_TRAIT_VALIDATION_ASSERTIONS; ?>,
+        <?php echo PHPFHIR_TRAIT_SOURCE_XMLNS; ?>;
 
-    /** @var null|\DOMElement */
-    private null|\DOMElement $_node = null;
+    /** @var null|string */
+    private null|string $_xhtml = null;
 
     /**
      * <?php echo PHPFHIR_XHTML_TYPE_NAME; ?> Constructor
-     * @param null|string|\DOMNode $node
-     * @param null|<?php echo $config->getNamespace(true); ?>\<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config
+     * @param null|string|\DOMNode|\SimpleXMLElement $xhtml
+     */
+    public function __construct(null|string|\DOMNode|\SimpleXmlElement $xhtml = null)
+    {
+        $this->setXhtml($xhtml);
+    }
+
+    /**
+     * @return string
      */
-    public function __construct(null|string|\DOMNode $node = null, null|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config = null)
+    public function _getFhirTypeName(): string
     {
-        $this->setNode($node, $config);
+        return 'Xhtml';
     }
 
     /**
-     * @return null|\DOMNode
+     * @return array
      */
-    public function getNode(): null|\DOMNode
+    public function _getValidationRules(): array
     {
-        return $this->_node;
+        return [];
     }
 
     /**
-     * @param null|string|\DOMNode $node
-     * @param null|<?php echo $config->getNamespace(true); ?>\<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config
+     * @return array
+     */
+    public function _getValidationErrors(): array
+    {
+        return [];
+    }
+
+    /**
+     * @return null|string
+     */
+    public function getXhtml(): null|string
+    {
+        return $this->_xhtml;
+    }
+
+    /**
+     * @param null|string|\DOMNode|\SimpleXmlElement $xhtml
      * @return static
      */
-    public function setNode(null|string|\DOMNode $node, null|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config = null): self
+    public function setXhtml(null|string|\DOMNode|\SimpleXMLElement $xhtml): self
     {
-        if (null === $node) {
-            $this->_trackValueSet($this->_node, null);
-            $this->_node = null;
+        if (null === $xhtml) {
+            $this->_trackValueSet($this->_xhtml, null);
+            $this->_xhtml = null;
             return $this;
         }
+        if ($xhtml instanceof \DOMDocument) {
+            $xhtml = $xhtml->saveXML($xhtml->documentElement);
+        } else if ($xhtml instanceof \DOMNode) {
+            $xhtml = $xhtml->ownerDocument->saveXML($xhtml);
+        } else if ($xhtml instanceof \SimpleXMLElement) {
+            $xhtml = $xhtml->asXML();
+        }
+        $this->_trackValueSet($this->_xhtml, $xhtml);
+        $this->_xhtml = $xhtml;
+        return $this;
+    }
+
+    /**
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config
+     * @return null|\SimpleXMLElement
+     * @throws \Exception
+     */
+    public function getSimpleXMLElement(null|<?php echo PHPFHIR_CLASSNAME_CONFIG; ?> $config = null): null|\SimpleXMLElement
+    {
+        $xhtml = $this->getXhtml();
+        if (null === $xhtml) {
+            return null;
+        }
         if (null === $config) {
             $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
         }
-        $dom = $config->newDOMDocument();
-        if (is_string($node)) {
-            $dom->loadHTML($node);
-        } else if ($node instanceof \DOMDocument) {
-            $dom->appendChild($dom->importNode($node->documentElement, true));
-        } else {
-            $dom->appendChild($dom->importNode($node, true));
-        }
-        $newNode = $dom->documentElement;
-        while (null !== $newNode) {
-            if (in_array(strtolower($newNode->nodeName), self::_NOISE_NODES, true)) {
-                $newNode = $newNode->firstChild;
-            } else {
-                break;
-            }
-        }
-        if ('' !== ($ens = (string)$newNode?->namespaceURI)) {
-            $this->_setFHIRXMLNamespace($ens);
-        }
-        $this->_trackValueSet($this->_node, $newNode);
-        $this->_node = $newNode;
-        return $this;
+        return new \SimpleXMLElement($xhtml, $config->getLibxmlOpts());
+    }
+
+    /**
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config
+     * @return null|\DOMDocument
+     */
+    public function getDOMDocument(null|<?php echo PHPFHIR_CLASSNAME_CONFIG; ?> $config = null): null|\DOMDocument
+    {
+        $xhtml = $this->getXhtml();
+        if (null === $xhtml) {
+            return null;
+        }
+        if (null === $config) {
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+        }
+        $dom = new \DOMDocument('1.0', 'UTF-8');
+        $dom->loadXML($xhtml, $config->getLibxmlOpts());
+        return $dom;
+    }
+
+    /**
+     * Returns open \XMLReader instance with content read
+     *
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_CONFIG); ?> $config
+     * @return null|\XMLReader
+     */
+    public function getXMLReader(null|<?php echo PHPFHIR_CLASSNAME_CONFIG; ?> $config = null): null|\XMLReader
+    {
+        $xhtml = $this->getXhtml();
+        if (null === $xhtml) {
+            return null;
+        }
+        if (null === $config) {
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+        }
+        $xr = \XMLReader::XML($xhtml, 'UTF-8', $config->getLibxmlOpts());
+        $xr->read();
+        return $xr;
     }
 
 <?php
@@ -132,45 +194,53 @@ public function setNode(null|string|\DOMNode $node, null|<?php echo PHPFHIR_INTE
     ]
 );
 ?>
-        $type->setNode($element);
+        $type->setXhtml($element);
         return $type;
     }
 
     /**
-     * @param null|\DOMElement $element
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
-     * @return \DOMElement
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?> $xw
+     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_CLASSNAME_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @return <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?>
+
      */
-    public function xmlSerialize(\DOMElement $element = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): \DOMElement
+    public function xmlSerialize(null|<?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?> $xw = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>
+
     {
         if (is_int($config)) {
-            $libxmlOpts = $config;
-            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>([<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::LIBXML_OPTS->value => $config]);
         } else if (null === $config) {
-            $libxmlOpts = <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_LIBXML_OPTS;
             $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
-        } else {
-            $libxmlOpts = $config->getLibxmlOpts();
         }
-        if (null === $element) {
-            $dom = $config->newDOMDocument();
-            $dom->loadXML($this->_getFHIRXMLElementDefinition('<?php echo $xmlName; ?>'), $libxmlOpts);
-            $element = $dom->documentElement;
-        } else if ('' !== ($ns = $this->_getFHIRXMLNamespace())) {
-            $element->setAttribute('xmlns', $ns);
+        if (null === $xw) {
+            $xw = new <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>();
+        }
+        if (!$xw->isOpen()) {
+            $xw->openMemory();
+        }
+        if (!$xw->isDocStarted()) {
+            $docStarted = true;
+            $xw->startDocument();
         }
-        $node = $this->getNode();
-        if (null === $node) {
-            return $element;
+        if (!$xw->isRootOpen()) {
+            $rootOpened = true;
+            $xw->openRootNode($config, 'Xhtml', $this->_getSourceXmlns());
         }
-        for ($i = 0; $i < $node->attributes->length; $i++) {
-            $attr = $node->attributes->item($i);
-            $element->setAttribute($attr->nodeName, $attr->nodeValue);
+        $xr = $this->getXMLReader($config);
+        if (null === $xr) {
+            return $xw;
         }
-        for ($i = 0; $i < $node->childNodes->length; $i++) {
-            $element->appendChild($element->ownerDocument->importNode($node->childNodes->item($i), true));
+        while ($xr->moveToNextAttribute()) {
+            $xw->writeAttribute($xr->name, $xr->value);
         }
-        return $element;
+        $xw->writeRaw($xr->readInnerXml());
+        if (isset($rootOpened) && $rootOpened) {
+            $xw->endElement();
+        }
+        if (isset($docStarted) && $docStarted) {
+            $xw->endDocument();
+        }
+        return $xw;
     }
 
     /**
@@ -178,8 +248,11 @@ public function xmlSerialize(\DOMElement $element = null, null|int|<?php echo PH
      */
     public function jsonSerialize(): mixed
     {
-        $node = $this->getNode();
-        return $node?->ownerDocument->saveXML($node);
+        $xhtml = $this->getXhtml();
+        if (null === $xhtml) {
+            return null;
+        }
+        return (string)$xhtml;
     }
 
     /**
@@ -187,6 +260,6 @@ public function jsonSerialize(): mixed
      */
     public function __toString(): string
     {
-        return $this->jsonSerialize() ?? '';
+        return (string)$this->getXhtml();
     }
 }<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/methods/common.php b/template/types/methods/common.php
index b677b429..cacc66be 100644
--- a/template/types/methods/common.php
+++ b/template/types/methods/common.php
@@ -31,7 +31,7 @@
     /**
      * @return string
      */
-    public function _getFHIRTypeName(): string
+    public function _getFhirTypeName(): string
     {
         return self::FHIR_TYPE_NAME;
     }
diff --git a/template/types/methods/constructors/primitive.php b/template/types/methods/constructors/primitive.php
index 6ac08b5d..14f9a503 100644
--- a/template/types/methods/constructors/primitive.php
+++ b/template/types/methods/constructors/primitive.php
@@ -48,7 +48,7 @@ public function __construct(<?php echo TypeHintUtils::primitiveValuePropertyType
             $this->setValue($value);
         } elseif (is_array($value)) {
             parent::__construct($value);
-            if (isset($value[self::FIELD_VALUE])) {
+            if (array_key_exists(self::FIELD_VALUE, $value)) {
                 $this->setValue($value[self::FIELD_VALUE]);
             }
         } else {
diff --git a/template/types/methods/constructors/property_setter_default.php b/template/types/methods/constructors/property_setter_default.php
index 8bb21132..05ecf69b 100644
--- a/template/types/methods/constructors/property_setter_default.php
+++ b/template/types/methods/constructors/property_setter_default.php
@@ -24,13 +24,10 @@
 $setter = $property->getSetterName();
 
 ob_start(); ?>
-        if (isset($data[self::<?php echo $propertyFieldConst; ?>])) {
+        if (array_key_exists(self::<?php echo $propertyFieldConst; ?>, $data)) {
 <?php if ($property->isCollection()) : ?>
             if (is_array($data[self::<?php echo $propertyFieldConst; ?>])) {
                 foreach($data[self::<?php echo $propertyFieldConst; ?>] as $v) {
-                    if (null === $v) {
-                        continue;
-                    }
                     if ($v instanceof <?php echo $propertyTypeClassName; ?>) {
                         $this-><?php echo $setter; ?>($v);
                     } else {
diff --git a/template/types/methods/constructors/property_setter_primitive.php b/template/types/methods/constructors/property_setter_primitive.php
index e9fc8ef1..a51d9a63 100644
--- a/template/types/methods/constructors/property_setter_primitive.php
+++ b/template/types/methods/constructors/property_setter_primitive.php
@@ -22,13 +22,10 @@
 $setter = $property->getSetterName();
 
 ob_start(); ?>
-        if (isset($data[self::<?php echo $propertyFieldConst; ?>])) {
+        if (array_key_exists(self::<?php echo $propertyFieldConst; ?>, $data)) {
 <?php if ($property->isCollection()) : ?>
             if (is_array($data[self::<?php echo $propertyFieldConst; ?>])) {
                 foreach($data[self::<?php echo $propertyFieldConst; ?>] as $v) {
-                    if (null === $v) {
-                        continue;
-                    }
                     $this-><?php echo $setter; ?>($v);
                 }
             } else {
diff --git a/template/types/methods/constructors/property_setter_primitive_container.php b/template/types/methods/constructors/property_setter_primitive_container.php
index 9336b894..b1afb79f 100644
--- a/template/types/methods/constructors/property_setter_primitive_container.php
+++ b/template/types/methods/constructors/property_setter_primitive_container.php
@@ -27,7 +27,7 @@
 // these types are a pain in the ass
 
 ob_start(); ?>
-        if (isset($data[self::<?php echo $propertyFieldConst; ?>]) || isset($data[self::<?php echo $propertyFieldConstExt; ?>])) {
+        if (array_key_exists(self::<?php echo $propertyFieldConst; ?>, $data) || array_key_exists(self::<?php echo $propertyFieldConstExt; ?>, $data)) {
             $value = $data[self::<?php echo $propertyFieldConst; ?>] ?? null;
             $ext = (isset($data[self::<?php echo $propertyFieldConstExt; ?>]) && is_array($data[self::<?php echo $propertyFieldConstExt; ?>])) ? $data[self::<?php echo $propertyFieldConstExt; ?>] : [];
             if (null !== $value) {
@@ -59,6 +59,8 @@
 <?php else : ?>
                 $this-><?php echo $setter; ?>(new <?php echo $propertyTypeClassName; ?>($ext));
 <?php endif; ?>
+            } else {
+                $this-><?php echo $setter; ?>(new <?php echo $propertyTypeClassName; ?>(null));
             }
         }
 <?php
diff --git a/template/types/properties/methods/default/setter_contained_resource.php b/template/types/properties/methods/default/setter_contained_resource.php
index c1d8befb..4e9f272f 100644
--- a/template/types/properties/methods/default/setter_contained_resource.php
+++ b/template/types/properties/methods/default/setter_contained_resource.php
@@ -36,7 +36,7 @@
 <?php echo $documentation; ?>
      *<?php endif; ?>
 
-     * @param null|<?php echo $config->getNamespace(true) . '\\' . PHPFHIR_INTERFACE_CONTAINED_TYPE; ?> $<?php echo $propertyName; ?>
+     * @param null|<?php echo $config->getFullyQualifiedName(true) . '\\' . PHPFHIR_INTERFACE_CONTAINED_TYPE; ?> $<?php echo $propertyName; ?>
 
      * @return static
      */
diff --git a/template/types/properties/methods/default/setter_contained_resource_collection.php b/template/types/properties/methods/default/setter_contained_resource_collection.php
index a746befc..990617fa 100644
--- a/template/types/properties/methods/default/setter_contained_resource_collection.php
+++ b/template/types/properties/methods/default/setter_contained_resource_collection.php
@@ -38,7 +38,7 @@
 <?php echo $documentation; ?>
      *<?php endif; ?>
 
-     * @param <?php echo $config->getNamespace(true) . '\\' . PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>[] $<?php echo $propertyName; ?>
+     * @param <?php echo $config->getFullyQualifiedName(true) . '\\' . PHPFHIR_INTERFACE_CONTAINED_TYPE; ?>[] $<?php echo $propertyName; ?>
 
      * @return static
      */
diff --git a/template/types/serialization/xml.php b/template/types/serialization/xml.php
index 0023bb81..ac9fb460 100644
--- a/template/types/serialization/xml.php
+++ b/template/types/serialization/xml.php
@@ -92,6 +92,12 @@
         );
     }
 } ?>
-        return $element;
+        if (isset($openedRoot) && $openedRoot) {
+            $xw->endElement();
+        }
+        if (isset($docStarted) && $docStarted) {
+            $xw->endDocument();
+        }
+        return $xw;
     }
 <?php return ob_get_clean();
diff --git a/template/types/serialization/xml/serialize/body.php b/template/types/serialization/xml/serialize/body.php
index 3334e3dc..469e11e6 100644
--- a/template/types/serialization/xml/serialize/body.php
+++ b/template/types/serialization/xml/serialize/body.php
@@ -16,28 +16,56 @@
  * limitations under the License.
  */
 
+use DCarbone\PHPFHIR\Enum\TypeKind;
+
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Type $type */
 /** @var \DCarbone\PHPFHIR\Definition\Type|null $parentType */
 /** @var \DCarbone\PHPFHIR\Definition\Property[] $localProperties */
 
 ob_start();
+// TODO(@dcarbone): improve efficiency here a bit
+
+// this logic is repeated as we must set attributes before defining child elements.
+
 foreach ($localProperties as $property) {
-    if (null !== $property->getValueFHIRType()) {
+    if ($property->isCollection()) {
+        continue;
+    }
+    $pt = $property->getValueFHIRType();
+    if (null === $pt) {
         echo require_with(
-            __DIR__ . DIRECTORY_SEPARATOR . 'body_typed.php',
+            __DIR__ . DIRECTORY_SEPARATOR . 'body_untyped.php',
             [
                 'config' => $config,
-                'property' => $property,
             ]
         );
-    } elseif (0 < count($localProperties)) {
+    } else if ($pt->hasPrimitiveParent() || $pt->getKind() === TypeKind::PRIMITIVE) {
         echo require_with(
-            __DIR__ . DIRECTORY_SEPARATOR . 'body_untyped.php',
+            __DIR__ . DIRECTORY_SEPARATOR . 'body_typed.php',
             [
                 'config' => $config,
+                'property' => $property,
             ]
         );
     }
 }
+
+if ($type->hasParentWithLocalProperties()) : ?>
+        parent::xmlSerialize($xw, $config);
+<?php endif;
+
+foreach ($localProperties as $property) {
+    $pt = $property->getValueFHIRType();
+    if (!$property->isCollection() && (null === $pt || $pt->hasPrimitiveParent() || $pt->getKind() === TypeKind::PRIMITIVE)) {
+        continue;
+    }
+    echo require_with(
+        __DIR__ . DIRECTORY_SEPARATOR . 'body_typed.php',
+        [
+            'config' => $config,
+            'property' => $property,
+        ]
+    );
+}
 return ob_get_clean();
diff --git a/template/types/serialization/xml/serialize/body_typed.php b/template/types/serialization/xml/serialize/body_typed.php
index 9b0017a8..d9484658 100644
--- a/template/types/serialization/xml/serialize/body_typed.php
+++ b/template/types/serialization/xml/serialize/body_typed.php
@@ -24,7 +24,7 @@
 $propertyTypeKind = $property->getValueFHIRType()->getKind();
 
 ob_start();
-if ($propertyTypeKind->isOneOf(TypeKind::RESOURCE_CONTAINER, TypeKind::RESOURCE_INLINE)) :
+if ($propertyTypeKind->isOneOf(TypeKind::RESOURCE_CONTAINER, TypeKind::RESOURCE_INLINE)) {
     echo require_with(
         __DIR__ . DIRECTORY_SEPARATOR . 'body_typed_resource_container.php',
         [
@@ -32,7 +32,15 @@
             'property' => $property,
         ]
     );
-else :
+} else if ($propertyTypeKind === TypeKind::PHPFHIR_XHTML) {
+    echo require_with(
+        __DIR__ . DIRECTORY_SEPARATOR . 'body_typed_xhtml.php',
+        [
+            'config' => $config,
+            'property' => $property,
+        ]
+    );
+} else {
     echo require_with(
         __DIR__ . DIRECTORY_SEPARATOR . 'body_typed_default.php',
         [
@@ -40,5 +48,5 @@
             'property' => $property,
         ]
     );
-endif;
+}
 return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/serialize/body_typed_default.php b/template/types/serialization/xml/serialize/body_typed_default.php
index 9c02b823..41bb9965 100644
--- a/template/types/serialization/xml/serialize/body_typed_default.php
+++ b/template/types/serialization/xml/serialize/body_typed_default.php
@@ -18,6 +18,7 @@
 
 use DCarbone\PHPFHIR\Enum\TypeKind;
 
+/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Property $property */
 
 $propertyType = $property->getValueFHIRType();
@@ -26,24 +27,19 @@
 
 ob_start();
 if ($property->isCollection()) : // collection fields ?>
-        if ([] !== ($vs = $this-><?php echo $getter; ?>())) {
-            foreach($vs as $v) {
-                if (null === $v) {
-                    continue;
-                }
-                $telement = $element->ownerDocument->createElement(self::<?php echo $propertyConstName; ?>);
-                $element->appendChild($telement);
-                $v->xmlSerialize($telement);
-            }
+        foreach ($this-><?php echo $getter; ?>() as $v) {
+            $xw->startElement(self::<?php echo $propertyConstName; ?>);
+            $v->xmlSerialize($xw, $config);
+            $xw->endElement();
         }
 <?php else : // single fields ?>
         if (null !== ($v = $this-><?php echo $getter; ?>())) {
 <?php if ($propertyType->hasPrimitiveParent() || $propertyType->getKind() === TypeKind::PRIMITIVE) : ?>
-            $element->setAttribute(self::<?php echo $propertyConstName; ?>, (string)$v);
+            $xw->writeAttribute(self::<?php echo $propertyConstName; ?>, $v->getFormattedValue());
 <?php else : ?>
-            $telement = $element->ownerDocument->createElement(self::<?php echo $propertyConstName; ?>);
-            $element->appendChild($telement);
-            $v->xmlSerialize($telement);
+            $xw->startElement(self::<?php echo $propertyConstName; ?>);
+            $v->xmlSerialize($xw, $config);
+            $xw->endElement();
 <?php endif; ?>
         }
 <?php endif;
diff --git a/template/types/serialization/xml/serialize/body_typed_resource_container.php b/template/types/serialization/xml/serialize/body_typed_resource_container.php
index 54422b8a..3ac239ad 100644
--- a/template/types/serialization/xml/serialize/body_typed_resource_container.php
+++ b/template/types/serialization/xml/serialize/body_typed_resource_container.php
@@ -25,23 +25,20 @@
 if ($property->isCollection()) : ?>
         if ([] !== ($vs = $this-><?php echo $getter; ?>())) {
             foreach($vs as $v) {
-                if (null === $v) {
-                    continue;
-                }
-                $e2 = $element->ownerDocument->createElement(self::<?php echo $propertyConstName; ?>);
-                $element->appendChild($e2);
-                $e3 = $element->ownerDocument->createElement($v->_getFHIRTypeName());
-                $e2->appendChild($e3);
-                $v->xmlSerialize($e3);
+                $xw->startElement(self::<?php echo $propertyConstName; ?>);
+                $xw->startElement($v->_getFhirTypeName());
+                $v->xmlSerialize($xw, $config);
+                $xw->endElement();
+                $xw->endElement();
             }
         }
 <?php else : ?>
         if (null !== ($v = $this-><?php echo $getter; ?>())) {
-            $e2 = $element->ownerDocument->createElement(self::<?php echo $propertyConstName; ?>);
-            $element->appendChild($e2);
-            $e3 = $element->ownerDocument->createElement($v->_getFHIRTypeName());
-            $e2->appendChild($e3);
-            $v->xmlSerialize($e3);
+            $xw->startElement(self::<?php echo $propertyConstName; ?>);
+            $xw->startElement($v->_getFhirTypeName());
+            $v->xmlSerialize($xw, $config);
+            $xw->endElement();
+            $xw->endElement();
         }
 <?php endif;
 return ob_get_clean();
diff --git a/template/types/serialization/xml/serialize/body_typed_xhtml.php b/template/types/serialization/xml/serialize/body_typed_xhtml.php
new file mode 100644
index 00000000..4593bec4
--- /dev/null
+++ b/template/types/serialization/xml/serialize/body_typed_xhtml.php
@@ -0,0 +1,30 @@
+<?php declare(strict_types=1);
+
+/*
+ * Copyright 2024 Daniel Carbone (daniel.p.carbone@gmail.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
+/** @var \DCarbone\PHPFHIR\Definition\Property $property */
+
+$getter = $property->getGetterName();
+
+ob_start(); ?>
+        if (null !== ($v = $this-><?php echo $getter; ?>())) {
+            $xw->startElement(self::<?php echo $property->getFieldConstantName(); ?>);
+            $v->xmlSerialize($xw, $config);
+            $xw->endElement();
+        }
+<?php return ob_get_clean();
diff --git a/template/types/serialization/xml/serialize/body_untyped.php b/template/types/serialization/xml/serialize/body_untyped.php
index 5d53e4da..f961108e 100644
--- a/template/types/serialization/xml/serialize/body_untyped.php
+++ b/template/types/serialization/xml/serialize/body_untyped.php
@@ -17,6 +17,6 @@
  */
 
 ob_start(); ?>
-        $element->setAttribute(self::FIELD_VALUE, (string)$this);
+        $xw->writeAttribute(self::FIELD_VALUE, $this->getFormattedValue());
 <?php
 return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/serialize/header.php b/template/types/serialization/xml/serialize/header.php
index 3286c4af..a28e4d35 100644
--- a/template/types/serialization/xml/serialize/header.php
+++ b/template/types/serialization/xml/serialize/header.php
@@ -23,36 +23,37 @@
 /** @var \DCarbone\PHPFHIR\Definition\Type $type */
 /** @var \DCarbone\PHPFHIR\Definition\Type $parentType */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 $typeKind = $type->getKind();
 $xmlName = NameUtils::getTypeXMLElementName($type);
 
 ob_start(); ?>
     /**
-     * @param null|\DOMElement $element
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
-     * @return \DOMElement<?php if ($typeKind !== TypeKind::PRIMITIVE || $type->hasParent()) : ?>
-
-     * @throws \DOMException<?php endif; ?>
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?> $xw
+     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_CLASSNAME_CONFIG; ?> $config PHP FHIR config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @return <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?>
 
      */
-    public function xmlSerialize(\DOMElement $element = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): \DOMElement
+    public function xmlSerialize(null|<?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?> $xw = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>
+
     {
         if (is_int($config)) {
-            $libxmlOpts = $config;
-            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>([<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::LIBXML_OPTS->value => $config]);
         } else if (null === $config) {
-            $libxmlOpts = <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_LIBXML_OPTS;
             $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
-        } else {
-            $libxmlOpts = $config->getLibxmlOpts();
         }
-        if (null === $element) {
-            $dom = $config->newDOMDocument();
-            $dom->loadXML($this->_getFHIRXMLElementDefinition('<?php echo $xmlName; ?>'), $libxmlOpts);
-            $element = $dom->documentElement;
+        if (null === $xw) {
+            $xw = new <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>();
+        }
+        if (!$xw->isOpen()) {
+            $xw->openMemory();
+        }
+        if (!$xw->isDocStarted()) {
+            $docStarted = true;
+            $xw->startDocument();
+        }
+        if (!$xw->isRootOpen()) {
+            $openedRoot = true;
+            $xw->openRootNode($config, '<?php echo NameUtils::getTypeXMLElementName($type); ?>', $this->_getSourceXmlns());
         }
-<?php if ($type->hasParentWithLocalProperties()) : ?>
-        parent::xmlSerialize($element);
-<?php endif;
-return ob_get_clean();
\ No newline at end of file
+<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/serialize/resource_container.php b/template/types/serialization/xml/serialize/resource_container.php
index bbff0112..912afd40 100644
--- a/template/types/serialization/xml/serialize/resource_container.php
+++ b/template/types/serialization/xml/serialize/resource_container.php
@@ -21,35 +21,42 @@
 /** @var \DCarbone\PHPFHIR\Config\VersionConfig $config */
 /** @var \DCarbone\PHPFHIR\Definition\Type $type */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 $localProperties = $type->getLocalProperties()->localPropertiesIterator();
 
 ob_start(); ?>
     /**
-     * @param null|\DOMElement $element
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
-     * @return \DOMElement
+     * @param null|<?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?> $xw
+     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_CLASSNAME_CONFIG; ?> $config PHP FHIR config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @return <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_XML_WRITER); ?>
+
      */
-    public function xmlSerialize(null|\DOMElement $element = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): \DOMElement
+    public function xmlSerialize(null|<?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?> $xw = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>
+
     {
         if (is_int($config)) {
-            $libxmlOpts = $config;
-            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>([<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::LIBXML_OPTS->value => $config]);
         } else if (null === $config) {
-            $libxmlOpts = <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_LIBXML_OPTS;
             $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
-        } else {
-            $libxmlOpts = $config->getLibxmlOpts();
+        }
+        if (null === $xw) {
+            $xw = new <?php echo PHPFHIR_CLASSNAME_XML_WRITER; ?>();
+        }
+        if (!$xw->isOpen()) {
+            $xw->openMemory();
+        }
+        if (!$xw->isDocStarted()) {
+            $docStarted = true;
+            $xw->startDocument();
         }
 <?php foreach($localProperties as $property) : ?>
-        if (null !== ($v = $this->get<?php echo $property->getGetterName(); ?>())) {
-            return $v->xmlSerialize($element, $libxmlOpts);
+        if (null !== ($v = $this-><?php echo $property->getGetterName(); ?>())) {
+            return $v->xmlSerialize($xw, $config);
         }
 <?php endforeach; ?>
-        if (null === $element) {
-            $dom = $config->newDOMDocument();
-            $dom->loadXML($this->_getFHIRXMLElementDefinition(<?php echo NameUtils::getTypeXMLElementName($type); ?>), $libxmlOpts);
-            $element = $dom->documentElement;
+        if (!$xw->isRootOpen()) {
+            $openedRoot = true;
+            $xw->openRootNode($config, '<?php echo NameUtils::getTypeXMLElementName($type); ?>', $this->_getSourceXmlns());
         }
 <?php
 return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/unserialize/body.php b/template/types/serialization/xml/unserialize/body.php
index 7555ed67..fb85bbb2 100644
--- a/template/types/serialization/xml/unserialize/body.php
+++ b/template/types/serialization/xml/unserialize/body.php
@@ -25,11 +25,8 @@
 ];
 
 ob_start(); ?>
-        for ($i = 0; $i < $element->childNodes->length; $i++) {
-            $n = $element->childNodes->item($i);
-            if (!($n instanceof \DOMElement)) {
-                continue;
-            }
+        foreach ($element->children() as $n) {
+            $childName = $n->getName();
 <?php foreach ($properties as $i => $property) {
     if (null !== $property->getValueFHIRType()) {
         echo require_with(
@@ -51,6 +48,7 @@
 }; ?>
 
         }
+        $attributes = $element->attributes();
 <?php foreach ($properties as $i => $property) {
     if (null !== $property->getValueFHIRType()) {
         echo require_with(
diff --git a/template/types/serialization/xml/unserialize/body_parse_attr_primitive.php b/template/types/serialization/xml/unserialize/body_parse_attr_primitive.php
index b7407aea..ddba335a 100644
--- a/template/types/serialization/xml/unserialize/body_parse_attr_primitive.php
+++ b/template/types/serialization/xml/unserialize/body_parse_attr_primitive.php
@@ -23,8 +23,7 @@
 $propType = $property->getValueFHIRType();
 
 ob_start(); ?>
-        $n = $element->attributes->getNamedItem(self::<?php echo $property->getFieldConstantName(); ?>);
-        if (null !== $n) {
-            $type->setValue($n->nodeValue);
+        if (isset($attributes[self::<?php echo $property->getFieldConstantName(); ?>])) {
+            $type->setValue((string)$attributes[self::<?php echo $property->getFieldConstantName(); ?>]);
         }
 <?php return ob_get_clean();
diff --git a/template/types/serialization/xml/unserialize/body_parse_attr_typed.php b/template/types/serialization/xml/unserialize/body_parse_attr_typed.php
index 9519b3d8..d9aa0ee8 100644
--- a/template/types/serialization/xml/unserialize/body_parse_attr_typed.php
+++ b/template/types/serialization/xml/unserialize/body_parse_attr_typed.php
@@ -28,17 +28,16 @@
 
 ob_start();
 if ($propertyType->getKind()->isOneOf(TypeKind::PRIMITIVE, TypeKind::LIST, TypeKind::PRIMITIVE_CONTAINER)) : ?>
-        $n = $element->attributes->getNamedItem(self::<?php echo $propertyConst; ?>);
-        if (null !== $n) {
-<?php if (!$property->isCollection()) : ?>
+        if (isset($attributes[self::<?php echo $propertyConst; ?>])) {
+<?php if ($property->isCollection()) : ?>
+            $type-><?php echo $setter; ?>((string)$attributes[self::<?php echo $propertyConst; ?>]);
+<?php else : ?>
             $pt = $type-><?php echo $property->getGetterName(); ?>();
             if (null !== $pt) {
-                $pt->setValue($n->nodeValue);
+                $pt->setValue((string)$attributes[self::<?php echo $propertyConst; ?>]);
             } else {
-                $type-><?php echo $setter; ?>($n->nodeValue);
+                $type-><?php echo $setter; ?>((string)$attributes[self::<?php echo $propertyConst; ?>]);
             }
-<?php else : ?>
-            $type-><?php echo $setter; ?>($n->nodeValue);
 <?php endif; ?>
         }
 <?php endif;
diff --git a/template/types/serialization/xml/unserialize/body_parse_node_primitive.php b/template/types/serialization/xml/unserialize/body_parse_node_primitive.php
index ddf51e3f..89478bdb 100644
--- a/template/types/serialization/xml/unserialize/body_parse_node_primitive.php
+++ b/template/types/serialization/xml/unserialize/body_parse_node_primitive.php
@@ -25,16 +25,13 @@
 $propConst = $property->getFieldConstantName();
 
 ob_start();
-if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propConst; ?> === $n->nodeName) {
-                $valueAttr = $n->attributes->getNamedItem('value');
+if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propConst; ?> === $childName) {
+                $valueAttr = $n->attributes()[self::FIELD_VALUE] ?? null;
                 if (null !== $valueAttr) {
-                    $type->setValue($valueAttr->nodeValue);
-                } elseif ($n->hasChildNodes()) {
-                    $type->setValue($n->ownerDocument->saveXML($n));
+                    $type->setValue((string)$valueAttr);
+                } elseif ($n->hasChildren()) {
+                    $type->setValue($n->saveXML());
                 } else {
-                    $type->setValue($n->textContent);
+                    $type->setValue((string)$n);
                 }
-<?php if (null !== $propType && $propType->getKind() === TypeKind::PHPFHIR_XHTML) : ?>
-                $type->_setElementName($n->nodeName);
-<?php endif; ?>
             }<?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/unserialize/body_parse_node_typed.php b/template/types/serialization/xml/unserialize/body_parse_node_typed.php
index ec7518c4..bf6abd2e 100644
--- a/template/types/serialization/xml/unserialize/body_parse_node_typed.php
+++ b/template/types/serialization/xml/unserialize/body_parse_node_typed.php
@@ -49,5 +49,4 @@
     )
 };
 
-
 return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/serialization/xml/unserialize/body_parse_node_typed_default.php b/template/types/serialization/xml/unserialize/body_parse_node_typed_default.php
index 5bb05f12..53007f7d 100644
--- a/template/types/serialization/xml/unserialize/body_parse_node_typed_default.php
+++ b/template/types/serialization/xml/unserialize/body_parse_node_typed_default.php
@@ -25,6 +25,6 @@
 $setter = $property->getSetterName();
 
 ob_start();
-if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propConst; ?> === $n->nodeName) {
-                $type-><?php echo $setter; ?>(<?php echo $propTypeClassname; ?>::xmlUnserialize($n));
+if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propConst; ?> === $childName) {
+                $type-><?php echo $setter; ?>(<?php echo $propTypeClassname; ?>::xmlUnserialize($n, null, $config));
             }<?php return ob_get_clean();
diff --git a/template/types/serialization/xml/unserialize/body_parse_node_typed_resource_container.php b/template/types/serialization/xml/unserialize/body_parse_node_typed_resource_container.php
index 109a648e..78f1aaa1 100644
--- a/template/types/serialization/xml/unserialize/body_parse_node_typed_resource_container.php
+++ b/template/types/serialization/xml/unserialize/body_parse_node_typed_resource_container.php
@@ -24,11 +24,8 @@
 $propertyConst = $property->getFieldConstantName();
 
 ob_start();
-if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propertyConst; ?> === $n->nodeName) {
-                for ($ni = 0; $ni < $n->childNodes->length; $ni++) {
-                    $nn = $n->childNodes->item($ni);
-                    if ($nn instanceof \DOMElement) {
-                        $type-><?php echo $setter; ?>(PHPFHIRTypeMap::getContainedTypeFromXML($nn));
-                    }
+if ($i > 0) : ?> else<?php else : ?>            <?php endif; ?>if (self::<?php echo $propertyConst; ?> === $childName) {
+                foreach ($n->children() as $nn) {
+                    $type-><?php echo $setter; ?>(<?php echo PHPFHIR_CLASSNAME_TYPEMAP; ?>::getContainedTypeFromXML($nn, $config));
                 }
             }<?php return ob_get_clean();
diff --git a/template/types/serialization/xml/unserialize/header.php b/template/types/serialization/xml/unserialize/header.php
index c925c1ab..b194d119 100644
--- a/template/types/serialization/xml/unserialize/header.php
+++ b/template/types/serialization/xml/unserialize/header.php
@@ -22,43 +22,29 @@
 /** @var null|\DCarbone\PHPFHIR\Definition\Type $parentType */
 /** @var string $typeClassName */
 
-$namespace = $config->getNamespace(false);
+$namespace = $config->getFullyQualifiedName(false);
 $versionName = $config->getVersion()->getName();
 
 ob_start(); ?>
     /**
-     * @param null|string|\DOMElement $element
+     * @param null|string|\SimpleXMLElement $element
      * @param null|<?php echo $type->getFullyQualifiedClassName(true); ?> $type
-     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?> $config XML serialization config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
+     * @param null|int|\<?php echo ('' === $namespace ? '' : "{$namespace}\\") . PHPFHIR_CLASSNAME_CONFIG; ?> $config PHP FHIR config.  Supports an integer value interpreted as libxml opts for backwards compatibility.
      * @return null|<?php echo $type->getFullyQualifiedClassName(true); ?>
 
      */
-    public static function xmlUnserialize(null|string|\DOMElement $element, null|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZABLE; ?> $type = null, null|int|<?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG ?> $config = null): null|self
+    public static function xmlUnserialize(null|string|\SimpleXMLElement $element, null|<?php echo PHPFHIR_INTERFACE_TYPE; ?> $type = null, null|int|<?php echo PHPFHIR_CLASSNAME_CONFIG ?> $config = null): null|self
     {
         if (null === $element) {
             return null;
         }
         if (is_int($config)) {
-            $libxmlOpts = $config;
-            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
+            $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>([<?php echo PHPFHIR_ENUM_CONFIG_KEY; ?>::LIBXML_OPTS->value => $config]);
         } else if (null === $config) {
-            $libxmlOpts = <?php echo PHPFHIR_INTERFACE_XML_SERIALIZALE_CONFIG; ?>::DEFAULT_LIBXML_OPTS;
             $config = new <?php echo PHPFHIR_CLASSNAME_CONFIG; ?>();
-        } else {
-            $libxmlOpts = $config->getLibxmlOpts();
         }
         if (is_string($element)) {
-            libxml_use_internal_errors(true);
-            $dom = $config->newDOMDocument();
-            if (false === $dom->loadXML($element, $libxmlOpts)) {
-                throw new \DomainException(sprintf(
-                    '%s::xmlUnserialize - String provided is not parseable as XML: %s',
-                    ltrim(substr(__CLASS__, (int)strrpos(__CLASS__, '\\')), '\\'),
-                    implode(', ', array_map(function(\libXMLError $err) { return $err->message; }, libxml_get_errors()))
-                ));
-            }
-            libxml_use_internal_errors(false);
-            $element = $dom->documentElement;
+            $element = new \SimpleXMLElement($element, $config->getLibxmlOpts());
         }
 <?php if ($type->isAbstract()) : // abstract types may not be instantiated directly ?>
         if (null === $type) {
@@ -74,7 +60,7 @@ public static function xmlUnserialize(null|string|\DOMElement $element, null|<?p
                 get_class($type)
             ));
         }
-        if ('' === $type->_getFHIRXMLNamespace() && '' !== ($ens = (string)$element->namespaceURI)) {
-            $type->_setFHIRXMLNamespace($ens);
+        if (null !== ($ns = $element->getNamespaces()[''] ?? null)) {
+            $type->_setSourceXmlns((string)$ns);
         }
 <?php return ob_get_clean();
\ No newline at end of file
diff --git a/template/types/tests/integration/class.php b/template/types/tests/integration/class.php
index 8c007cad..c2ce6f0c 100644
--- a/template/types/tests/integration/class.php
+++ b/template/types/tests/integration/class.php
@@ -68,8 +68,8 @@
 
 use <?php echo $bundleType->getFullyQualifiedClassName(false); ?>;
 use <?php echo $type->getFullyQualifiedClassName(false); ?>;
-use <?php echo $config->getNamespace(false); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?>;
-use <?php echo $config->getNamespace(false); ?>\<?php echo PHPFHIR_ENUM_TYPE; ?>;
+use <?php echo $config->getFullyQualifiedName(false, PHPFHIR_CLASSNAME_DEBUG_CLIENT); ?>;
+use <?php echo $config->getFullyQualifiedName(false, PHPFHIR_ENUM_TYPE); ?>;
 use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\TestCase;
 
@@ -81,7 +81,7 @@
  */
 class <?php echo $testClassname; ?> extends TestCase
 {
-    /** @var <?php echo $config->getNamespace(true); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?> */
+    /** @var <?php echo $config->getFullyQualifiedName(true, PHPFHIR_CLASSNAME_DEBUG_CLIENT); ?> */
     private <?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?> $client;
 
     /** @var array */
@@ -103,7 +103,11 @@ protected function fetchResource(string $format): string
         }
         $rc = $this->client->get(sprintf('/%s', <?php echo PHPFHIR_ENUM_TYPE; ?>::<?php echo $type->getConstName(false); ?>->value), ['_count' => '1', '_format' => $format]);
         $this->assertEmpty($rc->err, sprintf('curl error seen: %s', $rc->err));
-        $this->assertEquals(200, $rc->code, 'Expected 200 OK');
+        if (404 === $rc->code) {
+            $this->markTestSkipped(sprintf('Endpoint "%s" has no resources of type "%s"', $this->client->_getBaseUrl(), <?php echo PHPFHIR_ENUM_TYPE; ?>::<?php echo $type->getConstName(false); ?>->value));
+        } else {
+            $this->assertEquals(200, $rc->code, 'Expected 200 OK');
+        }
         $this->assertIsString($rc->resp);
         $this->_fetchedResources[$format] = $rc->resp;
         $fname = sprintf('%s%s<?php echo $type->getFHIRName(); ?>-<?php echo CopyrightUtils::getFHIRVersion(false); ?>-source.%s', PHPFHIR_OUTPUT_TMP_DIR, DIRECTORY_SEPARATOR, $format);
@@ -164,26 +168,26 @@ public function testXML(): void
 <?php else: ?>
         $resource = $entry->getResource();
 <?php endif; ?>
-        $resourceElement = $resource->xmlSerialize();
-        $resourceXML = $resourceElement->ownerDocument->saveXML($resourceElement);
+        $resourceXmlWriter = $resource->xmlSerialize();
+        $resourceXml = $resourceXmlWriter->outputMemory();
         try {
-            $type = <?php echo $type->getClassName(); ?>::xmlUnserialize($resourceXML);
+            $type = <?php echo $type->getClassName(); ?>::xmlUnserialize($resourceXml);
         } catch (\Exception $e) {
             throw new AssertionFailedError(
                 sprintf(
                     'Error building type "<?php echo $type->getFHIRName(); ?>" from XML: %s; XML: %s',
                     $e->getMessage(),
-                    $resourceXML
+                    $resourceXml
                 ),
                 $e->getCode(),
                 $e
             );
         }
         $this->assertInstanceOf(<?php echo $type->getClassName(); ?>::class, $type);
-        $typeElement = $type->xmlSerialize();
-        $this->assertEquals($resourceXML, $typeElement->ownerDocument->saveXML($typeElement));
-        $bundleElement = $bundle->xmlSerialize();
-        $this->assertXmlStringEqualsXmlString($sourceXML, $bundleElement->ownerDocument->saveXML());
+        $typeXmlWriter = $type->xmlSerialize();
+        $this->assertEquals($resourceXml, $typeXmlWriter->outputMemory());
+        $bundleXmlWriter = $bundle->xmlSerialize();
+        $this->assertXmlStringEqualsXmlString($sourceXML, $bundleXmlWriter->outputMemory());
     }
 
     public function testJSON(): void
diff --git a/template/types/tests/validation/class.php b/template/types/tests/validation/class.php
index 13a9a4df..1599c3ca 100644
--- a/template/types/tests/validation/class.php
+++ b/template/types/tests/validation/class.php
@@ -68,8 +68,8 @@
 
 use <?php echo $bundleType->getFullyQualifiedClassName(false); ?>;
 use <?php echo $type->getFullyQualifiedClassName(false); ?>;
-use <?php echo $config->getNamespace(false); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?>;
-use <?php echo $config->getNamespace(false); ?>\<?php echo PHPFHIR_ENUM_TYPE; ?>;
+use <?php echo $config->getFullyQualifiedName(false); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?>;
+use <?php echo $config->getFullyQualifiedName(false); ?>\<?php echo PHPFHIR_ENUM_TYPE; ?>;
 use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\TestCase;
 
@@ -102,7 +102,7 @@ class <?php echo $testClassname; ?> extends TestCase
         'If a code for the unit is present, the system SHALL also be present',
     ];
 
-    /** @var <?php echo $config->getNamespace(true); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?> */
+    /** @var <?php echo $config->getFullyQualifiedName(true); ?>\<?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?> */
     private <?php echo PHPFHIR_CLASSNAME_DEBUG_CLIENT; ?> $client;
 
     /** @var array */
@@ -214,7 +214,7 @@ public function testFHIRValidationXML(): void
 <?php else: ?>
         $resource = $entry->getResource();
 <?php endif; ?>
-        $fname = PHPFHIR_OUTPUT_TMP_DIR . DIRECTORY_SEPARATOR . $resource->_getFHIRTypeName() . '-<?php echo CopyrightUtils::getFHIRVersion(false); ?>.xml';
+        $fname = PHPFHIR_OUTPUT_TMP_DIR . DIRECTORY_SEPARATOR . $resource->_getFhirTypeName() . '-<?php echo CopyrightUtils::getFHIRVersion(false); ?>.xml';
         file_put_contents($fname, $bundle->xmlSerialize()->ownerDocument->saveXML());
         $this->assertFileExists($fname);
 
@@ -271,7 +271,7 @@ public function testFHIRValidationJSON()
 <?php else: ?>
         $resource = $entry->getResource();
 <?php endif; ?>
-        $fname = PHPFHIR_OUTPUT_TMP_DIR . DIRECTORY_SEPARATOR . $resource->_getFHIRTypeName() . '-<?php echo CopyrightUtils::getFHIRVersion(false); ?>.json';
+        $fname = PHPFHIR_OUTPUT_TMP_DIR . DIRECTORY_SEPARATOR . $resource->_getFhirTypeName() . '-<?php echo CopyrightUtils::getFHIRVersion(false); ?>.json';
         file_put_contents($fname, json_encode($bundle));
         $this->assertFileExists($fname);