diff --git a/composer.json b/composer.json
index 10b7d86..c3a3024 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
     "description": "Modern DOM library written in PHP for HTML documents",
     "type": "library",
     "require": {
-        "php": ">=7.1",
+        "php": ">=7.4",
         "ext-dom": "*",
         "mensbeam/html-parser": "dev-master"
     },
diff --git a/lib/AbstractDocument.php b/lib/Attr.php
similarity index 50%
rename from lib/AbstractDocument.php
rename to lib/Attr.php
index 3a6d1f1..d6a90dd 100644
--- a/lib/AbstractDocument.php
+++ b/lib/Attr.php
@@ -8,7 +8,7 @@
 declare(strict_types=1);
 namespace MensBeam\HTML\DOM;
 
-// Exists so Document can extend methods from its traits.
-abstract class AbstractDocument extends \DOMDocument {
-    use DocumentOrElement, MagicProperties, ParentNode, Walk;
+
+class Attr extends \DOMAttr {
+    use Node;
 }
diff --git a/lib/Document.php b/lib/Document.php
index be435ad..3ebf25c 100644
--- a/lib/Document.php
+++ b/lib/Document.php
@@ -11,7 +11,9 @@ use MensBeam\HTML\Parser,
     MensBeam\HTML\Parser\Data;
 
 
-class Document extends AbstractDocument {
+class Document extends \DOMDocument {
+    use DocumentOrElement, MagicProperties, ParentNode, Walk;
+
     protected $_body = null;
     /** Nonstandard */
     protected $_documentEncoding = null;
@@ -130,6 +132,7 @@ class Document extends AbstractDocument {
 
         parent::__construct();
 
+        $this->registerNodeClass('DOMAttr', '\MensBeam\HTML\DOM\Attr');
         $this->registerNodeClass('DOMDocument', '\MensBeam\HTML\DOM\Document');
         $this->registerNodeClass('DOMComment', '\MensBeam\HTML\DOM\Comment');
         $this->registerNodeClass('DOMDocumentFragment', '\MensBeam\HTML\DOM\DocumentFragment');
@@ -176,32 +179,33 @@ class Document extends AbstractDocument {
         }
     }
 
-    public function createAttributeNS($namespaceURI, $qualifiedName): \DOMAttr {
+    public function createAttributeNS(?string $namespace, string $qualifiedName): \DOMAttr {
         # The createAttributeNS(namespace, qualifiedName) method steps are:
         # 1. Let namespace, prefix, and localName be the result of passing namespace and
         #    qualifiedName to validate and extract.
-        [ 'namespace' => $namespaceURI, 'prefix' => $prefix, 'localName' => $localName ] = $this->validateAndExtract($qualifiedName, $namespaceURI);
+        [ 'namespace' => $namespace, 'prefix' => $prefix, 'localName' => $localName ] = $this->validateAndExtract($qualifiedName, $namespace);
 
         # 2. Return a new attribute whose namespace is namespace, namespace prefix is
         # prefix, local name is localName, and node document is this.
         // We need to do a couple more things here. PHP's XML-based DOM doesn't allow
         // some characters. We have to coerce them sometimes.
         try {
-            return parent::createAttributeNS($namespaceURI, $qualifiedName);
+            return parent::createAttributeNS($namespace, $qualifiedName);
         } catch (\DOMException $e) {
             // The element name is invalid for XML
             // Replace any offending characters with "UHHHHHH" where H are the
             //   uppercase hexadecimal digits of the character's code point
-            if ($namespaceURI !== null) {
-                $qualifiedName = implode(":", array_map([$this, "coerceName"], explode(":", $qualifiedName, 2)));
+            if ($namespace !== null) {
+                $qualifiedName = implode(':', array_map([ $this, 'coerceName' ], explode(':', $qualifiedName, 2)));
             } else {
                 $qualifiedName = $this->coerceName($qualifiedName);
             }
-            return parent::createAttributeNS($namespaceURI, $qualifiedName);
+
+            return parent::createAttributeNS($namespace, $qualifiedName);
         }
     }
 
-    public function createElement($name, $value = null): Element {
+    public function createElement(string $name, ?string $value = null): Element {
         # The createElement(localName, options) method steps are:
         // DEVIATION: We cannot follow the createElement parameters per the DOM spec
         // because we cannot change the parameters from \DOMDOcument. This is okay
@@ -415,92 +419,6 @@ class Document extends AbstractDocument {
     }
 
 
-    protected function preInsertionValidity(\DOMNode $node, ?\DOMNode $child = null) {
-        parent::preInsertionValidity($node, $child);
-
-        # 6. If parent is a document, and any of the statements below, switched on node,
-        # are true, then throw a "HierarchyRequestError" DOMException.
-        #
-        # DocumentFragment node
-        #    If node has more than one element child or has a Text node child.
-        #    Otherwise, if node has one element child and either parent has an element
-        #    child, child is a doctype, or child is non-null and a doctype is following
-        #    child.
-        if ($node instanceof \DOMDocumentType) {
-            if ($node->childNodes->length > 1 || $node->firstChild instanceof Text) {
-                throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-            } else {
-                if ($node->firstChild instanceof \DOMDocumentType) {
-                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                }
-
-                foreach ($this->childNodes as $c) {
-                    if ($c instanceof Element) {
-                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                    }
-                }
-
-                if ($child !== null) {
-                    $n = $child;
-                    while ($n = $n->nextSibling) {
-                        if ($n instanceof \DOMDocumentType) {
-                            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                        }
-                    }
-                }
-            }
-        }
-        # element
-        #    parent has an element child, child is a doctype, or child is non-null and a
-        #    doctype is following child.
-        elseif ($node instanceof Element) {
-            if ($child instanceof \DOMDocumentType) {
-                throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-            }
-
-            if ($child !== null) {
-                $n = $child;
-                while ($n = $n->nextSibling) {
-                    if ($n instanceof \DOMDocumentType) {
-                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                    }
-                }
-            }
-
-            foreach ($this->childNodes as $c) {
-                if ($c instanceof Element) {
-                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                }
-            }
-        }
-
-        # doctype
-        #    parent has a doctype child, child is non-null and an element is preceding
-        #    child, or child is null and parent has an element child.
-        elseif ($node instanceof \DOMDocumentType) {
-            foreach ($this->childNodes as $c) {
-                if ($c instanceof \DOMDocumentType) {
-                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                }
-            }
-
-            if ($child !== null) {
-                $n = $child;
-                while ($n = $n->prevSibling) {
-                    if ($n instanceof Element) {
-                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                    }
-                }
-            } else {
-                foreach ($this->childNodes as $c) {
-                    if ($c instanceof Element) {
-                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
-                    }
-                }
-            }
-        }
-    }
-
     protected function serializeBlockElementFilter(\DOMNode $ignoredNode): \Closure {
         $blockElementFilter = function($n) use ($ignoredNode) {
             if (!$n->isSameNode($ignoredNode) && $n instanceof Element && $this->isHTMLNamespace($n) && (in_array($n->nodeName, self::BLOCK_ELEMENTS) || $n->walk(function($nn) {
diff --git a/lib/DocumentFragment.php b/lib/DocumentFragment.php
index a87f069..b14815b 100644
--- a/lib/DocumentFragment.php
+++ b/lib/DocumentFragment.php
@@ -8,8 +8,48 @@
 declare(strict_types=1);
 namespace MensBeam\HTML\DOM;
 
+
 class DocumentFragment extends \DOMDocumentFragment {
-    use ParentNode, Walk;
+    use MagicProperties, ParentNode, Walk;
+
+    protected $_host = null;
+
+    protected function __get_host(): ?\DOMNode {
+        if ($this->_host === null) {
+            return $this->_host;
+        }
+
+        return $this->_host->get();
+    }
+
+    protected function __set_host(\DOMNode $value) {
+        if ($this->_host !== null) {
+            throw new Exception(Exception::READONLY_PROPERTY, 'host');
+        }
+
+        // Check to see if this is being set within the HTMLTemplateElement constructor
+        // and throw a read only exception otherwise. This will ensure the host remains
+        // readonly. YES. THIS IS DIRTY. We shouldn't do this, but there is no other
+        // option. While DocumentFragment could be created via a constructor it cannot
+        // be associated with a document unless created by
+        // Document::createDocumentFragment.
+        $backtrace = debug_backtrace();
+        $okay = false;
+        for ($len = count($backtrace), $i = $len - 1; $i >= 0; $i--) {
+            $cur = $backtrace[$i];
+            if ($cur['function'] === '__construct' && $cur['class'] === __NAMESPACE__ . '\\HTMLTemplateElement') {
+                $okay = true;
+                break;
+            }
+        }
+
+        if (!$okay) {
+            throw new Exception(Exception::READONLY_PROPERTY, 'host');
+        }
+
+        $this->_host = \WeakReference::create($value);
+    }
+
 
     public function __toString() {
         return $this->ownerDocument->saveHTML($this);
diff --git a/lib/Element.php b/lib/Element.php
index 0b76467..f142edc 100644
--- a/lib/Element.php
+++ b/lib/Element.php
@@ -17,16 +17,12 @@ class Element extends \DOMElement {
 
 
     protected function __get_classList(): ?TokenList {
-        // MensBeam\HTML\DOM\TokenList uses WeakReference to prevent a circular reference,
-        // so it requires PHP 7.4 to work.
-        if (version_compare(\PHP_VERSION, '7.4.0', '>=')) {
-            // Only create the class list if it is actually used.
-            if ($this->_classList === null) {
-                $this->_classList = new TokenList($this, 'class');
-            }
-            return $this->_classList;
+        // Only create the class list if it is actually used.
+        if ($this->_classList === null) {
+            $this->_classList = new TokenList($this, 'class');
         }
-        return null; // @codeCoverageIgnore
+
+        return $this->_classList;
     }
 
     protected function __get_innerHTML(): string {
diff --git a/lib/HTMLTemplateElement.php b/lib/HTMLTemplateElement.php
index 9062080..7138f15 100644
--- a/lib/HTMLTemplateElement.php
+++ b/lib/HTMLTemplateElement.php
@@ -24,7 +24,9 @@ class HTMLTemplateElement extends Element {
         $frag->removeChild($this);
         unset($frag);
 
-        $this->content = $this->ownerDocument->createDocumentFragment();
+        $content = $this->ownerDocument->createDocumentFragment();
+        $content->host = $this;
+        $this->content = $content;
     }
 
 
diff --git a/lib/traits/Node.php b/lib/traits/Node.php
index c5035dd..71e6915 100644
--- a/lib/traits/Node.php
+++ b/lib/traits/Node.php
@@ -21,4 +21,24 @@ trait Node {
     public function C14NFile($uri, $exclusive = null, $with_comments = null, ?array $xpath = null, ?array $ns_prefixes = null): bool {
         return false;
     }
+
+    public function getRootNode(): ?\DOMNode {
+        # The getRootNode(options) method steps are to return this’s shadow-including
+        # root if options["composed"] is true; otherwise this’s root.
+        // DEVIATION: This implementation does not have scripting, so there's no Shadow
+        // DOM. Therefore, there isn't a need for the options parameter.
+
+        # The root of an object is itself, if its parent is null, or else it is the root
+        # of its parent. The root of a tree is any object participating in that tree
+        # whose parent is null.
+        if ($this->parentNode === null) {
+            return $this;
+        }
+
+        return $this->moonwalk(function($n) {
+            if ($n->parentNode === null) {
+                return true;
+            }
+        })->current();
+    }
 }
diff --git a/lib/traits/ParentNode.php b/lib/traits/ParentNode.php
index 39458ec..7630735 100644
--- a/lib/traits/ParentNode.php
+++ b/lib/traits/ParentNode.php
@@ -120,41 +120,137 @@ trait ParentNode {
         // "parent" in the spec comments below is $this
 
         # 1. If parent is not a Document, DocumentFragment, or Element node, then throw
-        # a "HierarchyRequestError" DOMException.
+        #    a "HierarchyRequestError" DOMException.
         // Not necessary because they've been disabled and return hierarchy request
-        // errors in "leaf nodes".
+        // errors in ChildNode trait.
 
         # 2. If node is a host-including inclusive ancestor of parent, then throw a
-        # "HierarchyRequestError" DOMException.
+        #    "HierarchyRequestError" DOMException.
         #
         # An object A is a host-including inclusive ancestor of an object B, if either
         # A is an inclusive ancestor of B, or if B’s root has a non-null host and A is a
         # host-including inclusive ancestor of B’s root’s host.
-        // DEVIATION: The baseline for this library is PHP 7.1, and without
-        // WeakReferences we cannot add a host property to DocumentFragment to check
-        // against.
-        // This is handled just fine by PHP's DOM.
+        if ($node->parentNode !== null) {
+            if ($this->isSameNode($node) || $this->moonwalk(function($n) use($node) {
+                if ($n->isSameNode($node)) {
+                    return true;
+                }
+            })->current() !== null) {
+                throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+            } else {
+                $parentRoot = $this->getRootNode();
+                $parentRootHost = $parentRoot->host;
+                if ($parentRoot instanceof DocumentFragment && $parentRootHost !== null && ($host->isSameNode($node) || $host->moonwalk(function($n) use($node) {
+                    if ($n->isSameNode($node)) {
+                        return true;
+                    }
+                })->current() !== null)) {
+                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                }
+            }
+        }
 
         # 3. If child is non-null and its parent is not parent, then throw a
-        # "NotFoundError" DOMException.
-        // This is handled just fine by PHP's DOM.
+        #    "NotFoundError" DOMException.
+        if ($child !== null && ($child->parentNode === null || !$child->parentNode->isSameNode($this))) {
+            throw new DOMException(DOMException::NOT_FOUND);
+        }
 
         # 4. If node is not a DocumentFragment, DocumentType, Element, Text,
-        # ProcessingInstruction, or Comment node, then throw a "HierarchyRequestError"
-        # DOMException.
+        #    ProcessingInstruction, or Comment node, then throw a "HierarchyRequestError"
+        #    DOMException.
         if (!$node instanceof DocumentFragment && !$node instanceof \DOMDocumentType && !$node instanceof Element && !$node instanceof Text && !$node instanceof ProcessingInstruction && !$node instanceof Comment) {
             throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
         }
 
         # 5. If either node is a Text node and parent is a document, or node is a
-        # doctype and parent is not a document, then throw a "HierarchyRequestError"
-        # DOMException.
+        #    doctype and parent is not a document, then throw a "HierarchyRequestError"
+        #    DOMException.
         // Not necessary because they've been disabled and return hierarchy request
-        // errors in "leaf nodes".
+        // errors in ChildNode trait
 
         # 6. If parent is a document, and any of the statements below, switched on node,
-        # are true, then throw a "HierarchyRequestError" DOMException.
-        // Handled by the Document class.
+        #    are true, then throw a "HierarchyRequestError" DOMException.
+        if ($this instanceof Document) {
+            # DocumentFragment node
+            #    If node has more than one element child or has a Text node child.
+            #    Otherwise, if node has one element child and either parent has an element
+            #    child, child is a doctype, or child is non-null and a doctype is following
+            #    child.
+            if ($node instanceof \DOMDocumentType) {
+                if ($node->childNodes->length > 1 || $node->firstChild instanceof Text) {
+                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                } else {
+                    if ($node->firstChild instanceof \DOMDocumentType) {
+                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                    }
+
+                    foreach ($this->childNodes as $c) {
+                        if ($c instanceof Element) {
+                            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                        }
+                    }
+
+                    if ($child !== null) {
+                        $n = $child;
+                        while ($n = $n->nextSibling) {
+                            if ($n instanceof \DOMDocumentType) {
+                                throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                            }
+                        }
+                    }
+                }
+            }
+            # element
+            #    parent has an element child, child is a doctype, or child is non-null and a
+            #    doctype is following child.
+            elseif ($node instanceof Element) {
+                if ($child instanceof \DOMDocumentType) {
+                    throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                }
+
+                if ($child !== null) {
+                    $n = $child;
+                    while ($n = $n->nextSibling) {
+                        if ($n instanceof \DOMDocumentType) {
+                            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                        }
+                    }
+                }
+
+                foreach ($this->childNodes as $c) {
+                    if ($c instanceof Element) {
+                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                    }
+                }
+            }
+
+            # doctype
+            #    parent has a doctype child, child is non-null and an element is preceding
+            #    child, or child is null and parent has an element child.
+            elseif ($node instanceof \DOMDocumentType) {
+                foreach ($this->childNodes as $c) {
+                    if ($c instanceof \DOMDocumentType) {
+                        throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                    }
+                }
+
+                if ($child !== null) {
+                    $n = $child;
+                    while ($n = $n->prevSibling) {
+                        if ($n instanceof Element) {
+                            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                        }
+                    }
+                } else {
+                    foreach ($this->childNodes as $c) {
+                        if ($c instanceof Element) {
+                            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+                        }
+                    }
+                }
+            }
+        }
     }
 
 
diff --git a/tests/cases/TestDocument.php b/tests/cases/TestDocument.php
index 10702b2..0bd5bf9 100644
--- a/tests/cases/TestDocument.php
+++ b/tests/cases/TestDocument.php
@@ -43,11 +43,27 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
     }
 
 
+    /**
+     * @covers \MensBeam\HTML\DOM\Document::createAttribute
+     */
+    public function testAttributeNodeCreationFailure(): void {
+        $this->expectException(DOMException::class);
+        $this->expectExceptionCode(DOMException::INVALID_CHARACTER);
+        $d = new Document();
+        $d->createAttribute('<ook>');
+    }
+
+
     public function provideAttributeNodeNSCreation(): iterable {
         return [
-            [ 'fake_ns', 'test',      'test', '' ],
-            [ 'fake_ns', 'test:test', 'test', 'test' ],
-            [ 'fake_ns', 'TEST:TEST', 'TEST', 'TEST' ]
+            [ 'fake_ns',         'test',             'fake_ns',         '',     'test' ],
+            [ 'fake_ns',         'test:test',        'fake_ns',         'test', 'test' ],
+            [ 'fake_ns',         'TEST:TEST',        'fake_ns',         'TEST', 'TEST' ],
+            [ 'another_fake_ns', 'steaming💩:poop💩', 'another_fake_ns', 'steamingU01F4A9', 'poopU01F4A9' ],
+            // An empty string for a prefix is technically incorrect, but we cannot fix that.
+            [ '',                'poop💩',            null,              '',                'poopU01F4A9' ],
+            // An empty string for a prefix is technically incorrect, but we cannot fix that.
+            [ null,              'poop💩',            null,              '',                'poopU01F4A9' ]
         ];
     }
 
@@ -56,13 +72,13 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
      * @covers \MensBeam\HTML\DOM\Document::createAttributeNS
      * @covers \MensBeam\HTML\DOM\Document::validateAndExtract
      */
-    public function testAttributeNodeNSCreation(?string $nsIn, string $nameIn, string $local, string $prefix): void {
+    public function testAttributeNodeNSCreation(?string $nsIn, string $nameIn, ?string $nsExpected, ?string $prefixExpected, string $localNameExpected): void {
         $d = new Document();
         $d->appendChild($d->createElement('html'));
         $a = $d->createAttributeNS($nsIn, $nameIn);
-        $this->assertSame($local, $a->localName);
-        $this->assertSame($nsIn, $a->namespaceURI);
-        $this->assertSame($prefix, $a->prefix);
+        $this->assertSame($nsExpected, $a->namespaceURI);
+        $this->assertSame($prefixExpected, $a->prefix);
+        $this->assertSame($localNameExpected, $a->localName);
     }
 
 
@@ -117,8 +133,9 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
         $d2 = new Document();
         $d2->appendChild($d2->createElement('html'));
         $d2->loadDOM($d);
-        $this->assertSame('MensBeam\HTML\DOM\Element', $d2->firstChild::class);
-        $this->assertSame('html', $d2->firstChild->nodeName);
+        $d3 = new Document($d);
+        $this->assertSame('MensBeam\HTML\DOM\Element', $d3->firstChild::class);
+        $this->assertSame('html', $d3->firstChild->nodeName);
 
         // Test file source
         $vfs = vfsStream::setup('DOM', 0777, [ 'test.html' => <<<HTML
@@ -166,12 +183,14 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
         return [
             // HTML element
             [ 'div',         'div',      Element::class ],
-            // HTML element and uppercase local name
+            // HTML element and uppercase qualified name
             [ 'DIV',         'div',      Element::class ],
             // Template element
             [ 'template',    'template', HTMLTemplateElement::class ],
-            // Template element and uppercase local name
-            [ 'TEMPLATE',    'template', HTMLTemplateElement::class ]
+            // Template element and uppercase qualified name
+            [ 'TEMPLATE',    'template', HTMLTemplateElement::class ],
+            // Name coercion
+            [ 'poop💩',       'poopU01F4A9',   Element::class ]
         ];
     }
 
@@ -179,29 +198,56 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
      * @dataProvider provideElementCreation
      * @covers \MensBeam\HTML\DOM\Document::createElement
      */
-    public function testElementCreation(string $localIn, string $localOut, string $class): void {
+    public function testElementCreation(string $nameIn, string $nameExpected, string $classExpected): void {
         $d = new Document;
-        $n = $d->createElement($localIn);
-        $this->assertInstanceOf($class, $n);
+        $n = $d->createElement($nameIn);
+        $this->assertInstanceOf($classExpected, $n);
         $this->assertNotNull($n->ownerDocument);
-        $this->assertSame($localOut, $n->localName);
+        $this->assertSame($nameExpected, $n->nodeName);
+    }
+
+
+    public function provideElementCreationFailures(): iterable {
+        return [
+            [ function() {
+                $d = new Document();
+                $d->createElement('ook', 'FAIL');
+            }, DOMException::NOT_SUPPORTED ],
+            [ function() {
+                $d = new Document();
+                $d->createElement('<ook>');
+            }, DOMException::INVALID_CHARACTER ]
+        ];
+    }
+
+
+    /**
+     * @dataProvider provideElementCreationFailures
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     */
+    public function testElementCreationFailures(\Closure $closure, int $errorCode): void {
+        $this->expectException(DOMException::class);
+        $this->expectExceptionCode($errorCode);
+        $closure();
     }
 
 
     public function provideElementCreationNS(): iterable {
         return [
             // HTML element with a null namespace
-            [ null,                   null,                   'div',      'div',      Element::class ],
+            [ null,                   null,                   'div',      'div',           Element::class ],
             // Template element with a null namespace
-            [ null,                   null,                   'template', 'template', HTMLTemplateElement::class ],
+            [ null,                   null,                   'template', 'template',      HTMLTemplateElement::class ],
             // Template element with a null namespace and uppercase name
-            [ null,                   null,                   'TEMPLATE', 'TEMPLATE', HTMLTemplateElement::class ],
+            [ null,                   null,                   'TEMPLATE', 'TEMPLATE',      HTMLTemplateElement::class ],
             // Template element
-            [ Parser::HTML_NAMESPACE, Parser::HTML_NAMESPACE, 'template', 'template', HTMLTemplateElement::class ],
+            [ Parser::HTML_NAMESPACE, Parser::HTML_NAMESPACE, 'template', 'template',      HTMLTemplateElement::class ],
             // SVG element with SVG namespace
-            [ Parser::SVG_NAMESPACE,  Parser::SVG_NAMESPACE,  'svg',      'svg',      Element::class ],
+            [ Parser::SVG_NAMESPACE,  Parser::SVG_NAMESPACE,  'svg',      'svg',           Element::class ],
             // SVG element with SVG namespace and uppercase local name
-            [ Parser::SVG_NAMESPACE,  Parser::SVG_NAMESPACE,  'SVG',      'SVG',      Element::class ]
+            [ Parser::SVG_NAMESPACE,  Parser::SVG_NAMESPACE,  'SVG',      'SVG',           Element::class ],
+            // Name coercion
+            [ 'steaming💩',           'steaming💩',            'poop💩',   'poopU01F4A9',   Element::class ]
         ];
     }
 
@@ -210,13 +256,42 @@ class TestDocument extends \PHPUnit\Framework\TestCase {
      * @covers \MensBeam\HTML\DOM\Document::createElementNS
      * @covers \MensBeam\HTML\DOM\Document::validateAndExtract
      */
-    public function testElementCreationNS(?string $nsIn, ?string $nsOut, string $localIn, string $localOut, string $class): void {
+    public function testElementCreationNS(?string $nsIn, ?string $nsExpected, string $localNameIn, string $localNameExpected, string $classExpected): void {
         $d = new Document();
-        $n = $d->createElementNS($nsIn, $localIn);
-        $this->assertInstanceOf($class, $n);
+        $n = $d->createElementNS($nsIn, $localNameIn);
+        $this->assertInstanceOf($classExpected, $n);
         $this->assertNotNull($n->ownerDocument);
-        $this->assertSame($nsOut, $n->namespaceURI);
-        $this->assertSame($localOut, $n->localName);
+        $this->assertSame($nsExpected, $n->namespaceURI);
+        $this->assertSame($localNameExpected, $n->localName);
+    }
+
+
+    public function provideElementCreationNSFailures(): iterable {
+        return [
+            [ function() {
+                $d = new Document();
+                $d->createElementNS('ook', 'ook', 'FAIL');
+            }, DOMException::NOT_SUPPORTED ],
+            [ function() {
+                $d = new Document();
+                $d->createElementNS(null, '<ook>');
+            }, DOMException::INVALID_CHARACTER ],
+            [ function() {
+                $d = new Document();
+                $d->createElementNS(null, 'xmlns');
+            }, DOMException::NAMESPACE_ERROR ]
+        ];
+    }
+
+    /**
+     * @dataProvider provideElementCreationNSFailures
+     * @covers \MensBeam\HTML\DOM\Document::createElementNS
+     * @covers \MensBeam\HTML\DOM\Document::validateAndExtract
+     */
+    public function testElementCreationNSFailures(\Closure $closure, int $errorCode): void {
+        $this->expectException(DOMException::class);
+        $this->expectExceptionCode($errorCode);
+        $closure();
     }
 
 
diff --git a/tests/cases/serializer/TestSerializer.php b/tests/cases/serializer/TestSerializer.php
index 022f62e..a3827fb 100644
--- a/tests/cases/serializer/TestSerializer.php
+++ b/tests/cases/serializer/TestSerializer.php
@@ -8,7 +8,10 @@
 declare(strict_types=1);
 namespace MensBeam\HTML\DOM\TestCase;
 
-use MensBeam\HTML\DOM\Document;
+use MensBeam\HTML\DOM\{
+    Document,
+    DOMException
+};
 use MensBeam\HTML\Parser;
 
 /**
@@ -150,4 +153,43 @@ class TestSerializer extends \PHPUnit\Framework\TestCase {
         }
         return $out;
     }
+
+
+    /** @covers \MensBeam\HTML\DOM\Document::saveHTML */
+    public function testSerializingDocumentType(): void {
+        $d = new Document();
+        $dt = $d->implementation->createDocumentType('ook', 'eek', 'ack');
+        $d->appendChild($dt);
+        $this->assertSame('<!DOCTYPE ook>', $d->saveHTML($dt));
+    }
+
+
+    /**
+     * @covers \MensBeam\HTML\DOM\Document::saveHTML
+     * @covers \MensBeam\HTML\DOM\Document::serializeFragment
+     * @covers \MensBeam\HTML\DOM\ToString::__toString
+     */
+    public function testSerializingElements(): void {
+        $d = new Document();
+        $i = $d->createElement('input');
+        $i->appendChild($d->createTextNode('You should not see this text'));
+        $this->assertSame('<input>', (string)$i);
+        $this->assertSame('', $d->saveHTML($i));
+
+        $t = $d->createElement('template');
+        $t->content->appendChild($d->createTextNode('Ook!'));
+        $this->assertSame('<template>Ook!</template>', (string)$t);
+        $this->assertSame('Ook!', $d->saveHTML($t));
+    }
+
+
+    /** @covers \MensBeam\HTML\DOM\Document::saveHTML */
+    public function testSerializerFailure(): void {
+        $this->expectException(DOMException::class);
+        $this->expectExceptionCode(DOMException::WRONG_DOCUMENT);
+        $d = new Document();
+        $h = $d->createElement('html');
+        $d2 = new Document();
+        $d2->saveHTML($h);
+    }
 }