diff --git a/README.md b/README.md
index 282f879..f0bc15e 100644
--- a/README.md
+++ b/README.md
@@ -45,61 +45,4 @@ This library and [masterminds/html5](https://packagist.org/packages/masterminds/
 
 † With HTML namespace disabled. With HTML namespace enabled it does not finish in a reasonable time due to a PHP bug.
 
-‡ With parse errors suppressed. Reporting parse errors adds approximately 10% overhead.
-
-## Document Object Model ##
-
-This library works by parsing HTML strings into PHP's existing XML DOM. It, however, has to force the antiquated PHP DOM extension into working properly with modern HTML DOM by extending many of the node types. The documentation below follows PHP's doc style guide with the exception of inherited methods and properties not being listed. Therefore, only new constants, properties, and methods will be listed; in addition, extended methods which change outward behavior from their parent class will be listed.
-
-### MensBeam\\HTML\\Document ###
-
-```php
-MensBeam\HTML\Document extends \DOMDocument {
-
-    /* Constants */
-    public const NO_QUIRKS_MODE = 0;
-    public const QUIRKS_MODE = 1;
-    public const LIMITED_QUIRKS_MODE = 2;
-
-    /* Properties */
-    public string|null $documentEncoding = null;
-    public int $quirksMode = 0;
-
-    /* Methods */
-    public load ( string $filename , null $options = null , string|null $encodingOrContentType = null ) : bool
-    public loadHTML ( string $source , null $options = null , string|null $encodingOrContentType = null ) : bool
-    public loadHTMLFile ( string $filename , null $options = null , string|null $encodingOrContentType = null ) : bool
-    public loadXML ( string $source , null $options = null ) : false
-    public save ( string $filename , null $options = null ) : int|false
-    public saveXML ( DOMNode|null $node = null , null $options = null ) : false
-    public validate ( ) : true
-    public xinclude ( null $options = null ) : false
-
-}
-```
-
-#### Properties ####
-
-<dl>
- <dt>documentEncoding</dt>
- <dd>Encoding of the document, as specified when parsing or when determining encoding type.</dd>
- <dt>quirksMode</dt>
- <dd>Used when parsing. Can be not in quirks mode, quirks mode, or limited quirks mode. See the `MensBeam\HTML\Document` constants to see the valid values.</dd>
-</dl>
-
-The following properties inherited from `\DOMDocument` have no effect on `Mensbeam\HTML\Document`:
-
-* actualEncoding
-* config
-* encoding
-* formatOutput
-* preserveWhiteSpace
-* recover
-* resolveExternals
-* standalone
-* substituteEntities
-* validateOnParse
-* version
-* xmlEncoding
-* xmlStandalone
-* xmlVersion
\ No newline at end of file
+‡ With parse errors suppressed. Reporting parse errors adds approximately 10% overhead.
\ No newline at end of file
diff --git a/lib/DOM/Comment.php b/lib/DOM/Comment.php
index 5d8e66a..d492b0c 100644
--- a/lib/DOM/Comment.php
+++ b/lib/DOM/Comment.php
@@ -7,7 +7,7 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class Comment extends \DOMComment {
-    use C14N, Moonwalk;
+    use Moonwalk, Node;
 
     public function __toString(): string {
         # Append the literal string "<!--" (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION
diff --git a/lib/DOM/DOMException.php b/lib/DOM/DOMException.php
index d2b980d..cdee808 100644
--- a/lib/DOM/DOMException.php
+++ b/lib/DOM/DOMException.php
@@ -12,6 +12,7 @@ class DOMException extends \Exception {
     const WRONG_DOCUMENT = 4;
     const INVALID_CHARACTER = 5;
     const NO_MODIFICATION_ALLOWED = 7;
+    const NOT_FOUND = 8;
     const SYNTAX_ERROR = 12;
 
     const DOCUMENT_ELEMENT_DOCUMENTFRAG_EXPECTED = 100;
@@ -23,6 +24,7 @@ class DOMException extends \Exception {
           4 => 'Supplied node does not belong to this document',
           5 => 'Invalid character',
           7 => 'Modification not allowed here',
+          8 => 'Not found error',
          12 => 'Syntax error',
         100 => 'Document, Element, or DocumentFragment expected; found %s',
         101 => 'The "%s" argument should be a string; found %s',
diff --git a/lib/DOM/Document.php b/lib/DOM/Document.php
index 7889f27..799762d 100644
--- a/lib/DOM/Document.php
+++ b/lib/DOM/Document.php
@@ -7,7 +7,7 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class Document extends \DOMDocument {
-    use C14N, EscapeString, Serialize, Walk;
+    use EscapeString, Node, Serialize, Walk;
 
     // Quirks mode constants
     public const NO_QUIRKS_MODE = 0;
@@ -29,21 +29,6 @@ class Document extends \DOMDocument {
         $this->registerNodeClass('DOMText', '\MensBeam\HTML\Text');
     }
 
-    public function appendChild($node) {
-        # If node is not a DocumentFragment, DocumentType, Element, Text,
-        # ProcessingInstruction, or Comment node then throw a "HierarchyRequestError"
-        # DOMException.
-        if (!$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);
-        }
-
-        $result = parent::appendChild($node);
-        if ($result !== false && $result instanceof TemplateElement) {
-            ElementRegistry::set($result);
-        }
-        return $result;
-    }
-
     public function createAttribute($name) {
         return $this->createAttributeNS(null, $name);
     }
@@ -85,7 +70,7 @@ class Document extends \DOMDocument {
             } else {
                 $e = new TemplateElement($this, $qualifiedName, $value);
                 // Template elements need to have a reference kept in userland
-                ElementRegistry::set($e);
+                ElementMap::set($e);
                 $e->content = $this->createDocumentFragment();
             }
 
@@ -108,26 +93,6 @@ class Document extends \DOMDocument {
         return false;
     }
 
-    public function insertBefore($node, $child = null) {
-        # If node is not a DocumentFragment, DocumentType, Element, Text,
-        # ProcessingInstruction, or Comment node then throw a "HierarchyRequestError"
-        # DOMException.
-        if (!$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);
-        }
-
-        $result = parent::insertBefore($node, $child);
-        if ($result !== false) {
-            if ($result instanceof TemplateElement) {
-                ElementRegistry::set($result);
-            }
-            if ($child instanceof TemplateElement) {
-                ElementRegistry::delete($child);
-            }
-        }
-        return $result;
-    }
-
     public function load($filename, $options = null, ?string $encodingOrContentType = null): bool {
         $data = Parser::fetchFile($filename, $encodingOrContentType);
         if (!$data) {
@@ -152,27 +117,6 @@ class Document extends \DOMDocument {
         return false;
     }
 
-    public function removeChild($child) {
-        $result = parent::removeChild($child);
-        if ($result !== false && $result instanceof TemplateElement) {
-            ElementRegistry::delete($child);
-        }
-        return $result;
-    }
-
-    public function replaceChild($node, $child) {
-        $result = parent::replaceChild($node, $child);
-        if ($result !== false) {
-            if ($result instanceof TemplateElement) {
-                ElementRegistry::set($child);
-            }
-            if ($child instanceof TemplateElement) {
-                ElementRegistry::delete($child);
-            }
-        }
-        return $result;
-    }
-
     public function save($filename, $options = null) {
         return file_put_contents($filename, $this->serialize());
     }
@@ -203,6 +147,10 @@ class Document extends \DOMDocument {
         return false;
     }
 
+    public function __destruct() {
+        ElementMap::destroy($this);
+    }
+
     public function __toString() {
         return $this->serialize();
     }
diff --git a/lib/DOM/DocumentFragment.php b/lib/DOM/DocumentFragment.php
index fb31a66..f6d6219 100644
--- a/lib/DOM/DocumentFragment.php
+++ b/lib/DOM/DocumentFragment.php
@@ -7,7 +7,7 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class DocumentFragment extends \DOMDocumentFragment {
-    use C14N, Moonwalk, Serialize;
+    use Moonwalk, Node, Serialize, Walk;
 
     public function __toString() {
         return $this->serialize();
diff --git a/lib/DOM/Element.php b/lib/DOM/Element.php
index bf1a512..5df0d0e 100644
--- a/lib/DOM/Element.php
+++ b/lib/DOM/Element.php
@@ -7,25 +7,10 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class Element extends \DOMElement {
-    use C14N, EscapeString, Moonwalk, Serialize, Walk;
+    use EscapeString, Moonwalk, Node, Serialize, Walk;
 
     protected $_classList;
 
-    public function appendChild($node) {
-        # If node is not a DocumentFragment, DocumentType, Element, Text,
-        # ProcessingInstruction, or Comment node then throw a "HierarchyRequestError"
-        # DOMException.
-        if (!$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);
-        }
-
-        $result = parent::appendChild($node);
-        if ($result !== false && $result instanceof TemplateElement) {
-            ElementRegistry::set($result);
-        }
-        return $result;
-    }
-
     public function getAttribute($name) {
         // Newer versions of the DOM spec have getAttribute return an empty string only
         // when the attribute exists and is empty, otherwise null. This fixes that.
@@ -48,45 +33,19 @@ class Element extends \DOMElement {
         return $value;
     }
 
-    public function insertBefore($node, $child = null) {
-        # If node is not a DocumentFragment, DocumentType, Element, Text,
-        # ProcessingInstruction, or Comment node then throw a "HierarchyRequestError"
-        # DOMException.
-        if (!$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);
-        }
+    public function isAncestorOf(\DOMNode $node): bool {
+        # An inclusive ancestor is an object or one of its ancestors.
+        #
+        # An object A is called an ancestor of an object B if and only if B is a
+        # descendant of A.
+        // object A is $this, object B is $node
+        $tree = $this->walk(function($n) use($node) {
+            if ($n->isSameNode($node)) {
+                return true;
+            }
+        });
 
-        $result = parent::insertBefore($node, $child);
-        if ($result !== false) {
-            if ($result instanceof TemplateElement) {
-                ElementRegistry::set($result);
-            }
-            if ($child instanceof TemplateElement) {
-                ElementRegistry::delete($child);
-            }
-        }
-        return $result;
-    }
-
-    public function removeChild($child) {
-        $result = parent::removeChild($child);
-        if ($result !== false && $result instanceof TemplateElement) {
-            ElementRegistry::delete($child);
-        }
-        return $result;
-    }
-
-    public function replaceChild($node, $child) {
-        $result = parent::replaceChild($node, $child);
-        if ($result !== false) {
-            if ($result instanceof TemplateElement) {
-                ElementRegistry::set($child);
-            }
-            if ($child instanceof TemplateElement) {
-                ElementRegistry::delete($child);
-            }
-        }
-        return $result;
+        return ($tree->current() !== null);
     }
 
     public function setAttribute($name, $value) {
diff --git a/lib/DOM/ElementRegistry.php b/lib/DOM/ElementMap.php
similarity index 76%
rename from lib/DOM/ElementRegistry.php
rename to lib/DOM/ElementMap.php
index 3e447a4..6187313 100644
--- a/lib/DOM/ElementRegistry.php
+++ b/lib/DOM/ElementMap.php
@@ -9,8 +9,8 @@ namespace MensBeam\HTML;
 // This is a write-only map of elements which need to be kept in memory; it
 // exists because values of properties on derived DOM classes are lost unless at
 // least one PHP reference is kept for the element somewhere in userspace. This
-// is that somewhere. It is at present only used for TemplateElements.
-class ElementRegistry {
+// is that somewhere. It is at present only used for template elements.
+class ElementMap {
     public static $_storage = [];
 
     public static function delete(Element $element) {
@@ -24,6 +24,14 @@ class ElementRegistry {
         return false;
     }
 
+    public static function destroy(Document $document) {
+        foreach (self::$_storage as $k => $v) {
+            if ($v->ownerDocument->isSameNode($document)) {
+                unset(self::$_storage[$k]);
+            }
+        }
+    }
+
     public static function has(Element $element) {
         foreach (self::$_storage as $v) {
             if ($v->isSameNode($element)) {
diff --git a/lib/DOM/ProcessingInstruction.php b/lib/DOM/ProcessingInstruction.php
index d2e8c6f..a7a9a9b 100644
--- a/lib/DOM/ProcessingInstruction.php
+++ b/lib/DOM/ProcessingInstruction.php
@@ -7,7 +7,7 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class ProcessingInstruction extends \DOMProcessingInstruction {
-    use C14N, Moonwalk;
+    use Moonwalk, Node;
 
     public function __toString(): string {
         # Append the literal string "<?" (U+003C LESS-THAN SIGN, U+003F QUESTION MARK),
diff --git a/lib/DOM/TemplateElement.php b/lib/DOM/TemplateElement.php
index d1ee817..d219ddc 100644
--- a/lib/DOM/TemplateElement.php
+++ b/lib/DOM/TemplateElement.php
@@ -22,4 +22,8 @@ class TemplateElement extends Element {
         $frag->removeChild($this);
         unset($frag);
     }
+
+    public function __destruct() {
+        ElementMap::delete($this);
+    }
 }
diff --git a/lib/DOM/Text.php b/lib/DOM/Text.php
index 2167234..16fa7e5 100644
--- a/lib/DOM/Text.php
+++ b/lib/DOM/Text.php
@@ -7,7 +7,7 @@ declare(strict_types=1);
 namespace MensBeam\HTML;
 
 class Text extends \DOMText {
-    use C14N, EscapeString, Moonwalk;
+    use EscapeString, Moonwalk, Node;
 
     function __toString(): string {
         # If the parent of current node is a style, script, xmp, iframe, noembed,
diff --git a/lib/DOM/traits/C14N.php b/lib/DOM/traits/C14N.php
deleted file mode 100644
index 8d4ead9..0000000
--- a/lib/DOM/traits/C14N.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-/** @license MIT
- * Copyright 2017 , Dustin Wilson, J. King et al.
- * See LICENSE and AUTHORS files for details */
-
-declare(strict_types=1);
-namespace MensBeam\HTML;
-
-// Disables C14N in extended DOM classes
-trait C14N {
-    public function C14N($exclusive = null, $with_comments = null, ?array $xpath = null, ?array $ns_prefixes = null): bool {
-        return false;
-    }
-
-    public function C14NFile($uri, $exclusive = null, $with_comments = null, ?array $xpath = null, ?array $ns_prefixes = null): bool {
-        return false;
-    }
-}
diff --git a/lib/DOM/traits/Node.php b/lib/DOM/traits/Node.php
new file mode 100644
index 0000000..8160f79
--- /dev/null
+++ b/lib/DOM/traits/Node.php
@@ -0,0 +1,191 @@
+<?php
+/** @license MIT
+ * Copyright 2017 , Dustin Wilson, J. King et al.
+ * See LICENSE and AUTHORS files for details */
+
+declare(strict_types=1);
+namespace MensBeam\HTML;
+
+// Extensions to PHP's DOM cannot inherit from an extended Node parent, so a
+// trait is the next best thing...
+trait Node {
+    protected function preInsertionValidity(\DOMNode $node, ?\DOMNode $child = null) {
+        // "parent" is $this
+
+        # 1. If parent is not a Document, DocumentFragment, or Element node,
+        # then throw a "HierarchyRequestError" DOMException.
+        if (!$this instanceof Document && !$this instanceof DocumentFragment && !$this instanceof Element) {
+            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+        }
+
+        # 2. If node is a host-including inclusive ancestor of parent, then
+        # throw a "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.
+        if ($node instanceof Element && $node->isAncestorOf($this)) {
+            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+        }
+
+        # 3. If child is non-null and its parent is not parent, then throw a
+        # "NotFoundError" DOMException.
+        if ($child !== null && !$child->parentNode->isSameNode($this)) {
+            throw new DOMException(DOMException::NOT_FOUND);
+        }
+
+        # 4. If node is not a DocumentFragment, DocumentType, Element,
+        # Text, ProcessingInstruction, or Comment node, then throw a
+        # "HierarchyRequestError" DOMException.
+        if (!$node instanceof DocumentFragment && !$node instanceof \DOMDocumentType && !$node instanceof Element && !$node instanceof Text && !$node instanceof ProcessingInstruction && !$node instanceof Comment) {
+            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+        }
+
+        # 5. If either node is a Text node and parent is a document, or
+        # node is a doctype and parent is not a document, then throw a
+        # "HierarchyRequestError" DOMException.
+        if (($node instanceof Text && $this instanceof Document) || ($node instanceof \DOMDocumentType && !$this instanceof Document)) {
+            throw new DOMException(DOMException::HIERARCHY_REQUEST_ERROR);
+        }
+
+        # 6. If parent is a document, and any of the statements below, switched
+        # on node, are true, then throw a "HierarchyRequestError" DOMException.
+        if ($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 ($node instanceof DocumentFragment) {
+                if ($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);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    public function appendChild($node) {
+        $this->preInsertionValidity($node);
+
+        $result = parent::appendChild($node);
+        if ($result !== false && $result instanceof TemplateElement) {
+            ElementMap::set($result);
+        }
+        return $result;
+    }
+
+    // Disable C14N
+    public function C14N($exclusive = null, $with_comments = null, ?array $xpath = null, ?array $ns_prefixes = null): bool {
+        return false;
+    }
+
+    // Disable C14NFile
+    public function C14NFile($uri, $exclusive = null, $with_comments = null, ?array $xpath = null, ?array $ns_prefixes = null): bool {
+        return false;
+    }
+
+    public function insertBefore($node, $child = null) {
+        $this->preInsertionValidity($node, $child);
+
+        $result = parent::insertBefore($node, $child);
+        if ($result !== false) {
+            if ($result instanceof TemplateElement) {
+                ElementMap::set($result);
+            }
+            if ($child instanceof TemplateElement) {
+                ElementMap::delete($child);
+            }
+        }
+        return $result;
+    }
+
+    public function removeChild($child) {
+        $result = parent::removeChild($child);
+        if ($result !== false && $result instanceof TemplateElement) {
+            ElementMap::delete($child);
+        }
+        return $result;
+    }
+
+    public function replaceChild($node, $child) {
+        $result = parent::replaceChild($node, $child);
+        if ($result !== false) {
+            if ($result instanceof TemplateElement) {
+                ElementMap::set($child);
+            }
+            if ($child instanceof TemplateElement) {
+                ElementMap::delete($child);
+            }
+        }
+        return $result;
+    }
+}