diff --git a/lib/CharacterData.php b/lib/CharacterData.php
index 26dd191..1f708d9 100644
--- a/lib/CharacterData.php
+++ b/lib/CharacterData.php
@@ -10,6 +10,8 @@ namespace MensBeam\HTML\DOM;
 
 
 abstract class CharacterData extends Node {
+    use ChildNode;
+
     protected function __get_data(): string {
         // PHP's DOM does this correctly already.
         return $this->innerNode->data;
diff --git a/lib/ChildNode.php b/lib/ChildNode.php
index 93e8a1b..a51bede 100644
--- a/lib/ChildNode.php
+++ b/lib/ChildNode.php
@@ -14,4 +14,127 @@ use MensBeam\HTML\DOM\Inner\{
 
 
 trait ChildNode {
+    public function after(Node|string ...$nodes): void {
+        // After exists in PHP DOM, but it can insert incorrect nodes because of PHP
+        // DOM's incorrect (for HTML) pre-insertion validation.
+
+        # The after(nodes) method steps are:
+        #
+        # 1. Let parent be this’s parent.
+        $inner = $this->innerNode;
+        $parent = $this->parentNode;
+
+        # 2. If parent is null, then return.
+        if ($parent === null) {
+            return;
+        }
+
+        # 3. Let viableNextSibling be this’s first following sibling not in nodes;
+        #    otherwise null.
+        $n = $inner;
+        $viableNextSibling = null;
+        while ($n = $n->nextSibling) {
+            foreach ($nodes as $nodeOrString) {
+                if ($nodeOrString instanceof Node && $this->getInnerNode($nodeOrString) === $n) {
+                    continue 2;
+                }
+            }
+
+            $viableNextSibling = $n;
+            break;
+        }
+
+        # 4. Let node be the result of converting nodes into a node, given nodes and this’s
+        #    node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 5. Pre-insert node into parent before viableNextSibling.
+        $parent->insertBefore($node, ($viableNextSibling !== null) ? $inner->ownerDocument->getWrapperNode($viableNextSibling) : null);
+    }
+
+    public function before(Node|string ...$nodes): void {
+        // Before exists in PHP DOM, but it can insert incorrect nodes because of PHP
+        // DOM's incorrect (for HTML) pre-insertion validation.
+
+        # The before(nodes) method steps are:
+        #
+        # 1. Let parent be this’s parent.
+        $inner = $this->innerNode;
+        $parent = $this->parentNode;
+
+        # 2. If parent is null, then return.
+        if ($parent === null) {
+            return;
+        }
+
+        # 3. Let viablePreviousSibling be this’s first preceding sibling not in nodes;
+        #    otherwise null.
+        $n = $inner;
+        $viablePreviousSibling = null;
+        while ($n = $n->previousSibling) {
+            foreach ($nodes as $nodeOrString) {
+                if ($nodeOrString instanceof Node && $this->getInnerNode($nodeOrString) === $n) {
+                    continue 2;
+                }
+            }
+
+            $viablePreviousSibling = $n;
+            break;
+        }
+
+        # 4. Let node be the result of converting nodes into a node, given nodes and
+        #    this’s node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 5. If viablePreviousSibling is null, then set it to parent’s first child;
+        #    otherwise to viablePreviousSibling’s next sibling.
+        $viablePreviousSibling = ($viablePreviousSibling === null) ? $parent->firstChild : $inner->ownerDocument->getWrapperNode($viablePreviousSibling->nextSibling);
+
+        # 6. Pre-insert node into parent before viablePreviousSibling.
+        $parent->insertBefore($node, $viablePreviousSibling);
+    }
+
+    public function replaceWith(Node|string ...$nodes): void {
+        // Before exists in PHP DOM, but it can insert incorrect nodes because of PHP
+        // DOM's incorrect (for HTML) pre-insertion validation.
+        # The replaceWith(nodes) method steps are:
+        #
+        # 1. Let parent be this’s parent.
+        $inner = $this->innerNode;
+        $parent = $this->parentNode;
+
+        # 2. If parent is null, then return.
+        if ($parent === null) {
+            return;
+        }
+
+        # 3. Let viableNextSibling be this’s first following sibling not in nodes;
+        #    otherwise null.
+        $n = $inner;
+        $viableNextSibling = null;
+        while ($n = $n->nextSibling) {
+            foreach ($nodes as $nodeOrString) {
+                if ($nodeOrString instanceof Node && $this->getInnerNode($nodeOrString) === $n) {
+                    continue 2;
+                }
+            }
+
+            $viableNextSibling = $n;
+            break;
+        }
+
+        # 4. Let node be the result of converting nodes into a node, given nodes and
+        #    this’s node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 5. If this’s parent is parent, replace this with node within parent.
+        # Note: This could have been inserted into node.
+        if ($this->parentNode === $parent) {
+            $parent->replaceChild($node, $this);
+        }
+        # 6. Otherwise, pre-insert node into parent before viableNextSibling.
+        else {
+            $parent->insertBefore($node, ($viableNextSibling !== null) ? $inner->ownerDocument->getWrapperNode($viableNextSibling) : null);
+        }
+    }
 }
diff --git a/lib/Inner/Document.php b/lib/Inner/Document.php
index 3ac4fde..26e55eb 100644
--- a/lib/Inner/Document.php
+++ b/lib/Inner/Document.php
@@ -112,7 +112,7 @@ class Document extends \DOMDocument {
                     $className = 'HTMLTemplateElement';
                 }
                 // This is done until we do element classes
-                elseif (in_array($name, [ 'a', 'abbr', 'address', 'area', 'article', 'aside', 'audio', 'b', 'base', 'bdi', 'bdo', 'blockquote', 'body', 'br', 'button', 'canvas', 'caption', 'cite', 'code', 'col', 'colgroup', 'content', 'data', 'datalist', 'dd', 'del', 'details', 'dfn', 'dialog', 'dir', 'div', 'dl', 'dt', 'em', 'embed', 'fieldset', 'figcaption', 'figure', 'font', 'footer', 'form', 'frame', 'frameset', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'head', 'header', 'hgroup', 'hr', 'i', 'iframe', 'img', 'img', 'input', 'ins', 'kbd', 'label', 'legend', 'li', 'link', 'main', 'map', 'mark', 'marquee', 'math', 'menu', 'menuitem', 'meta', 'meter', 'nav', 'noscript', 'object', 'ol', 'optgroup', 'option', 'output', 'p', 'param', 'picture', 'portal', 'pre', 'progress', 'q', 'rp', 'rt', 'ruby', 's', 'samp', 'script', 'section', 'select', 'shadow', 'slot', 'small', 'source', 'span', 'strong', 'style', 'sub', 'summary', 'sup', 'svg', 'table', 'tbody', 'td', 'template', 'textarea', 'tfoot', 'th', 'thead', 'time', 'title', 'tr', 'track', 'u', 'ul', 'var', 'video', 'wbr' ])) {
+                elseif (in_array($name, [ 'a', 'abbr', 'address', 'area', 'article', 'aside', 'audio', 'b', 'base', 'bdi', 'bdo', 'blockquote', 'body', 'br', 'button', 'canvas', 'caption', 'cite', 'code', 'col', 'colgroup', 'content', 'data', 'datalist', 'dd', 'del', 'details', 'dfn', 'dialog', 'dir', 'div', 'dl', 'dt', 'em', 'embed', 'fieldset', 'figcaption', 'figure', 'font', 'footer', 'form', 'frame', 'frameset', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'head', 'header', 'hgroup', 'hr', 'html', 'i', 'iframe', 'img', 'img', 'input', 'ins', 'kbd', 'label', 'legend', 'li', 'link', 'main', 'map', 'mark', 'marquee', 'math', 'menu', 'menuitem', 'meta', 'meter', 'nav', 'noscript', 'object', 'ol', 'optgroup', 'option', 'output', 'p', 'param', 'picture', 'portal', 'pre', 'progress', 'q', 'rp', 'rt', 'ruby', 's', 'samp', 'script', 'section', 'select', 'shadow', 'slot', 'small', 'source', 'span', 'strong', 'style', 'sub', 'summary', 'sup', 'svg', 'table', 'tbody', 'td', 'template', 'textarea', 'tfoot', 'th', 'thead', 'time', 'title', 'tr', 'track', 'u', 'ul', 'var', 'video', 'wbr' ])) {
                     $className = 'HTMLElement';
                 }
                 # If name is a valid custom element name, then return HTMLElement.
diff --git a/lib/Node.php b/lib/Node.php
index 4b020ad..268e4bb 100644
--- a/lib/Node.php
+++ b/lib/Node.php
@@ -981,6 +981,33 @@ abstract class Node {
         return false;
     }
 
+    protected function convertNodesToNode(array $nodes): Node {
+        # To convert nodes into a node, given nodes and document, run these steps:
+        # 1. Let node be null.
+        # 2. Replace each string in nodes with a new Text node whose data is the string
+        #    and node document is document.
+        # 3. If nodes contains one node, then set node to nodes[0].
+        # 4. Otherwise, set node to a new DocumentFragment node whose node document is
+        #    document, and then append each node in nodes, if any, to it.
+        // The spec would have us iterate through the provided nodes and then iterate
+        // through them again to append. Let's optimize this a wee bit, shall we?
+        $doc = (!$this instanceof Document) ? $this->ownerDocument : $this;
+        $node = (count($nodes) !== 1) ? $doc->createDocumentFragment() : null;
+        foreach ($nodes as $k => $n) {
+            if (is_string($n)) {
+                $n = $doc->createTextNode($n);
+            }
+
+            if ($node !== null) {
+                $node->appendChild($n);
+            } else {
+                $node = $n;
+            }
+        }
+
+        return $node;
+    }
+
     protected function getInnerDocument(): InnerDocument {
         return ($this instanceof Document) ? $this->innerNode : $this->innerNode->ownerDocument;
     }
@@ -1231,18 +1258,9 @@ abstract class Node {
         // below walks through this node and temporarily replaces foreign descendants
         // with bullshit elements which are then replaced once the node is inserted.
         if ($element->namespaceURI === null && ($this instanceof DocumentFragment || $this->getRootNode() !== null) && $element->hasChildNodes()) {
-            // XPath can't easily match just unprefixed elements, so we have to do this the
-            // old fashioned way by walking the DOM.
-            $foreign = $this->walkInner($element, function(\DOMNode $n) {
-                if ($n instanceof \DOMElement && ($n->parentNode !== null && $n->parentNode->namespaceURI === null) && $n->namespaceURI !== null && $n->prefix === '') {
-                    return self::WALK_ACCEPT | self::WALK_SKIP_CHILDREN;
-                }
-
-                return self::WALK_REJECT;
-            });
-
+            $foreign = $element->ownerDocument->xpath->query('.//*[parent::*[namespace-uri()=""] and not(namespace-uri()="") and name()=local-name()]', $element);
             $this->bullshitReplacements = [];
-            if ($foreign->current() !== null) {
+            if ($foreign->length > 0) {
                 $count = 0;
                 $doc = $this->getInnerDocument();
                 foreach ($foreign as $f) {
diff --git a/lib/ParentNode.php b/lib/ParentNode.php
index 9542c2b..c151970 100644
--- a/lib/ParentNode.php
+++ b/lib/ParentNode.php
@@ -16,6 +16,64 @@ use Symfony\Component\CssSelector\CssSelectorConverter,
 
 
 trait ParentNode {
+    protected function __get_childElementCount(): int {
+        return $this->innerNode->childElementCount;
+    }
+
+    protected function __get_children(): HTMLCollection {
+        $doc = $this->getInnerDocument();
+        // HTMLCollections cannot be created from their constructors normally.
+        return Reflection::createFromProtectedConstructor(__NAMESPACE__ . '\\HTMLCollection', $doc, $doc->xpath->query('.//*', $this->innerNode));
+    }
+
+    protected function __get_firstElementChild(): ?Element {
+        $result = $this->innerNode->firstElementChild;
+        return ($result !== null) ? $this->getInnerDocument()->getWrapperNode($result) : null;
+    }
+
+    protected function __get_lastElementChild(): ?Element {
+        $result = $this->innerNode->lastElementChild;
+        return ($result !== null) ? $this->getInnerDocument()->getWrapperNode($result) : null;
+    }
+
+
+    public function append(Node|string ...$nodes): void {
+        # The append(nodes) method steps are:
+        # 1. Let node be the result of converting nodes into a node given nodes and this’s
+        #    node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 2. Append node to this.
+        $this->appendChild($node);
+    }
+
+    public function prepend(Node|string ...$nodes): void {
+        # The prepend(nodes) method steps are:
+        # 1. Let node be the result of converting nodes into a node given nodes and this’s
+        #    node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 2. Pre-insert node into this before this’s first child.
+        $this->insertBefore($node, $this->firstChild);
+    }
+
+    public function replaceChildren(Node|string ...$nodes): void {
+        # The prepend(nodes) method steps are:
+        # 1. Let node be the result of converting nodes into a node given nodes and this’s
+        #    node document.
+        $node = $this->convertNodesToNode($nodes);
+
+        # 2. Ensure pre-insertion validity of node into this before null.
+        $this->preInsertionValidity($node);
+
+        # 3. Replace all with node within this.
+        while ($this->innerNode->hasChildNodes()) {
+            $this->innerNode->removeChild($this->innerNode->firstChild);
+        }
+
+        $this->appendChild($node);
+    }
+
     public function querySelector(string $selectors): ?Element {
         # The querySelector(selectors) method steps are to return the first result of
         # running scope-match a selectors string selectors against this, if the result
@@ -42,11 +100,11 @@ trait ParentNode {
      */
     public function walk(?\Closure $filter = null, bool $includeReferenceNode = false): \Generator {
         if ($this instanceof DocumentFragment || (!$this instanceof DocumentFragment && !$includeReferenceNode)) {
-            $node = $node->firstChild;
+            $node = $this->innerNode->firstChild;
         }
 
         if ($node !== null) {
-            $doc = (!$node instanceof InnerDocument) ? $node->ownerDocument : $node;
+            $doc = $this->getInnerDocument();
 
             do {
                 $next = $node->nextSibling;
@@ -63,11 +121,11 @@ trait ParentNode {
                     continue 2;
                     case Node::WALK_REJECT:
                     break;
-                    default: return;
+                    default: throw new DOMException(DOMException::SYNTAX_ERROR);
                 }
 
                 if ($node->parentNode !== null && $node->hasChildNodes()) {
-                    yield from $node->walk($filter);
+                    yield from $wrapperNode->walk($filter);
                 }
             } while ($node = $next);
         }
@@ -99,36 +157,4 @@ trait ParentNode {
         $nodeList = $this->getInnerDocument()->xpath->query($s, $this->innerNode);
         return $nodeList;
     }
-
-    protected function walkInner(\DOMNode $node, ?\Closure $filter = null, bool $includeReferenceNode = false): \Generator {
-        if (!$node instanceof DocumentFragment && !$includeReferenceNode) {
-            $node = $node->firstChild;
-        }
-
-        if ($node !== null) {
-            $doc = (!$node instanceof InnerDocument) ? $node->ownerDocument : $node;
-
-            do {
-                $next = $node->nextSibling;
-                $result = ($filter === null) ? Node::WALK_ACCEPT : $filter($node);
-
-                switch ($result) {
-                    case Node::WALK_ACCEPT:
-                        yield $node;
-                    break;
-                    case Node::WALK_ACCEPT | Node::WALK_SKIP_CHILDREN:
-                        yield $node;
-                    case Node::WALK_REJECT | Node::WALK_SKIP_CHILDREN:
-                    continue 2;
-                    case Node::WALK_REJECT:
-                    break;
-                    default: return;
-                }
-
-                if ($node->parentNode !== null && $node->hasChildNodes()) {
-                    yield from $this->walkInner($node, $filter);
-                }
-            } while ($node = $next);
-        }
-    }
 }
diff --git a/tests/cases/TestChildNode.php b/tests/cases/TestChildNode.php
new file mode 100644
index 0000000..4f48d6a
--- /dev/null
+++ b/tests/cases/TestChildNode.php
@@ -0,0 +1,67 @@
+<?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\DOM\TestCase;
+
+use MensBeam\HTML\DOM\{
+    Document,
+    DOMException,
+    Element,
+    Node
+};
+
+
+/** @covers \MensBeam\HTML\DOM\ChildNode */
+class TestChildNode extends \PHPUnit\Framework\TestCase {
+    public function testMethod_after_before_replaceWith(): void {
+        $d = new Document();
+        $d->appendChild($d->createElement('html'));
+        $body = $d->documentElement->appendChild($d->createElement('body'));
+        $div = $body->appendChild($d->createElement('div'));
+        $o = $body->appendChild($d->createTextNode('ook'));
+        $div2 = $body->appendChild($d->createElement('div'));
+
+        // On node with parent
+        $div->after($d->createElement('span'), $o, 'eek');
+        $this->assertSame('<body><div></div><span></span>ookeek<div></div></body>', (string)$body);
+        $div->after($o);
+        $this->assertSame('<body><div></div>ook<span></span>eek<div></div></body>', (string)$body);
+
+
+        // On node with no parent
+        $c = $d->createComment('ook');
+        $this->assertNull($c->after($d->createTextNode('ook')));
+
+        // On node with parent
+        $br = $body->insertBefore($d->createElement('br'), $div);
+        $e = $d->createTextNode('eek');
+        $div->before($d->createElement('span'), $o, 'eek', $e, $br);
+        $this->assertSame('<body><span></span>ookeekeek<br><div></div><span></span>eek<div></div></body>', (string)$body);
+        $div->before($o);
+        $this->assertSame('<body><span></span>eekeek<br>ook<div></div><span></span>eek<div></div></body>', (string)$body);
+
+        // On node with no parent
+        $c = $d->createComment('ook');
+        $this->assertNull($c->before($d->createTextNode('ook')));
+
+        // On node with parent
+        $s = $d->createElement('span');
+        $br->replaceWith('ack', $o, $e, $s);
+        $this->assertSame('<body><span></span>eekackookeek<span></span><div></div><span></span>eek<div></div></body>', (string)$body);
+        $s->replaceWith($o);
+        $this->assertSame('<body><span></span>eekackeekook<div></div><span></span>eek<div></div></body>', (string)$body);
+
+        // On node with no parent
+        $c = $d->createComment('ook');
+        $this->assertNull($c->replaceWith($d->createTextNode('ook')));
+
+        // Parent within node
+        $o->replaceWith('poo', $o, $e);
+        $this->assertSame('<body><span></span>eekackpooookeek<div></div><span></span>eek<div></div></body>', (string)$body);
+    }
+}
\ No newline at end of file
diff --git a/tests/cases/TestElement.php b/tests/cases/TestElement.php
index 75c074d..407adcd 100644
--- a/tests/cases/TestElement.php
+++ b/tests/cases/TestElement.php
@@ -422,10 +422,10 @@ class TestElement extends \PHPUnit\Framework\TestCase {
      * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
      * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
      * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
-     * @covers \MensBeam\HTML\DOM\ParentNode::walkInner
      * @covers \MensBeam\HTML\DOM\Text::__construct
      * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
      * @covers \MensBeam\HTML\DOM\Inner\Document::__get_wrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
      * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
      * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
      * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
diff --git a/tests/cases/TestNode.php b/tests/cases/TestNode.php
index 3686bd3..52eaac5 100644
--- a/tests/cases/TestNode.php
+++ b/tests/cases/TestNode.php
@@ -66,11 +66,11 @@ class TestNode extends \PHPUnit\Framework\TestCase {
      * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
      * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
      * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
-     * @covers \MensBeam\HTML\DOM\ParentNode::walkInner
      * @covers \MensBeam\HTML\DOM\ProcessingInstruction::__construct
      * @covers \MensBeam\HTML\DOM\Text::__construct
      * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
      * @covers \MensBeam\HTML\DOM\Inner\Document::__get_wrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
      * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
      * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
      * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
diff --git a/tests/cases/TestParentNode.php b/tests/cases/TestParentNode.php
index bc4078e..d404f3f 100644
--- a/tests/cases/TestParentNode.php
+++ b/tests/cases/TestParentNode.php
@@ -11,12 +11,148 @@ namespace MensBeam\HTML\DOM\TestCase;
 use MensBeam\HTML\DOM\{
     Document,
     DOMException,
+    Element,
     Node
 };
 
 
 /** @covers \MensBeam\HTML\DOM\ParentNode */
 class TestParentNode extends \PHPUnit\Framework\TestCase {
+    /**
+     * @covers \MensBeam\HTML\DOM\ParentNode::append
+     *
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Document::createDocumentFragment
+     * @covers \MensBeam\HTML\DOM\Document::createElement
+     * @covers \MensBeam\HTML\DOM\Document::createTextNode
+     * @covers \MensBeam\HTML\DOM\Document::load
+     * @covers \MensBeam\HTML\DOM\DocumentFragment::__construct
+     * @covers \MensBeam\HTML\DOM\DOMImplementation::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__get_innerHTML
+     * @covers \MensBeam\HTML\DOM\Node::__construct
+     * @covers \MensBeam\HTML\DOM\Node::__get_ownerDocument
+     * @covers \MensBeam\HTML\DOM\Node::appendChild
+     * @covers \MensBeam\HTML\DOM\Node::convertNodesToNode
+     * @covers \MensBeam\HTML\DOM\Node::getInnerDocument
+     * @covers \MensBeam\HTML\DOM\Node::getInnerNode
+     * @covers \MensBeam\HTML\DOM\Node::hasChildNodes
+     * @covers \MensBeam\HTML\DOM\Node::postInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
+     * @covers \MensBeam\HTML\DOM\NonElementParentNode::getElementById
+     * @covers \MensBeam\HTML\DOM\Text::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_wrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
+     * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::key
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::set
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::createFromProtectedConstructor
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::getProtectedProperty
+     */
+    public function testMethod_append(): void {
+        $d = new Document('<!DOCTYPE html><html><body><div>ook</div><div id="eek">eek</div></body></html>');
+        $eek = $d->getElementById('eek');
+        $eek->append('ook', $d->createElement('br'));
+        $eek->append('eek');
+        $this->assertSame('eekook<br>eek', $eek->innerHTML);
+    }
+
+
+    /**
+     * @covers \MensBeam\HTML\DOM\ParentNode::prepend
+     *
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Document::createDocumentFragment
+     * @covers \MensBeam\HTML\DOM\Document::createElement
+     * @covers \MensBeam\HTML\DOM\Document::createTextNode
+     * @covers \MensBeam\HTML\DOM\Document::load
+     * @covers \MensBeam\HTML\DOM\DocumentFragment::__construct
+     * @covers \MensBeam\HTML\DOM\DOMImplementation::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__get_innerHTML
+     * @covers \MensBeam\HTML\DOM\Node::__construct
+     * @covers \MensBeam\HTML\DOM\Node::__get_firstChild
+     * @covers \MensBeam\HTML\DOM\Node::__get_ownerDocument
+     * @covers \MensBeam\HTML\DOM\Node::appendChild
+     * @covers \MensBeam\HTML\DOM\Node::convertNodesToNode
+     * @covers \MensBeam\HTML\DOM\Node::getInnerDocument
+     * @covers \MensBeam\HTML\DOM\Node::getInnerNode
+     * @covers \MensBeam\HTML\DOM\Node::hasChildNodes
+     * @covers \MensBeam\HTML\DOM\Node::insertBefore
+     * @covers \MensBeam\HTML\DOM\Node::postInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
+     * @covers \MensBeam\HTML\DOM\NonElementParentNode::getElementById
+     * @covers \MensBeam\HTML\DOM\Text::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_wrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
+     * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::key
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::set
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::createFromProtectedConstructor
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::getProtectedProperty
+     */
+    public function testMethod_prepend(): void {
+        $d = new Document('<!DOCTYPE html><html><body><div>ook</div><div id="eek">eek</div></body></html>');
+        $eek = $d->getElementById('eek');
+        $eek->prepend('ook', $d->createElement('br'));
+        $this->assertSame('ook<br>eek', $eek->innerHTML);
+    }
+
+
+    /**
+     * @covers \MensBeam\HTML\DOM\ParentNode::replaceChildren
+     *
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Document::createDocumentFragment
+     * @covers \MensBeam\HTML\DOM\Document::createElement
+     * @covers \MensBeam\HTML\DOM\Document::createTextNode
+     * @covers \MensBeam\HTML\DOM\Document::load
+     * @covers \MensBeam\HTML\DOM\DocumentFragment::__construct
+     * @covers \MensBeam\HTML\DOM\DOMImplementation::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__get_innerHTML
+     * @covers \MensBeam\HTML\DOM\Node::__construct
+     * @covers \MensBeam\HTML\DOM\Node::__get_ownerDocument
+     * @covers \MensBeam\HTML\DOM\Node::appendChild
+     * @covers \MensBeam\HTML\DOM\Node::convertNodesToNode
+     * @covers \MensBeam\HTML\DOM\Node::getInnerDocument
+     * @covers \MensBeam\HTML\DOM\Node::getInnerNode
+     * @covers \MensBeam\HTML\DOM\Node::hasChildNodes
+     * @covers \MensBeam\HTML\DOM\Node::postInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
+     * @covers \MensBeam\HTML\DOM\NonElementParentNode::getElementById
+     * @covers \MensBeam\HTML\DOM\Text::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_wrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
+     * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::key
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::set
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::createFromProtectedConstructor
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::getProtectedProperty
+     */
+    public function testMethod_replaceChildren(): void {
+        $d = new Document('<!DOCTYPE html><html><body><div>ook</div><div id="eek">eek</div></body></html>');
+        $eek = $d->getElementById('eek');
+        $eek->replaceChildren('ook', $d->createElement('br'));
+        $this->assertSame('ook<br>', $eek->innerHTML);
+    }
+
+
     /**
      * @covers \MensBeam\HTML\DOM\ParentNode::querySelector
      * @covers \MensBeam\HTML\DOM\ParentNode::querySelectorAll
@@ -84,4 +220,129 @@ class TestParentNode extends \PHPUnit\Framework\TestCase {
         $d = new Document();
         $d->querySelector('fail?');
     }
+
+
+    /**
+     * @covers \MensBeam\HTML\DOM\ParentNode::walk
+     *
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Document::load
+     * @covers \MensBeam\HTML\DOM\DocumentType::__construct
+     * @covers \MensBeam\HTML\DOM\DOMImplementation::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__construct
+     * @covers \MensBeam\HTML\DOM\Node::__construct
+     * @covers \MensBeam\HTML\DOM\Node::getInnerDocument
+     * @covers \MensBeam\HTML\DOM\Node::hasChildNodes
+     * @covers \MensBeam\HTML\DOM\Node::postParsingTemplatesFix
+     * @covers \MensBeam\HTML\DOM\Text::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__get_xpath
+     * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::key
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::set
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::createFromProtectedConstructor
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::setProtectedProperties
+     */
+    public function testMethod_walk(): void {
+        $d = new Document(<<<HTML
+        <!DOCTYPE html>
+        <html>
+         <body>
+          <div>ook</div>
+          <div>
+           <div><p>Eek</p></div>
+           <div>
+            <div><p>Ook</p></div>
+           </div>
+          </div>
+         </body>
+        </html>
+        HTML);
+
+        // Empty filter -- walk over all nodes
+        $w = $d->walk();
+        $this->assertSame($d->doctype, $w->current());
+        foreach ($w as $node);
+
+        // Simple accept on element and reject everything else filter
+        $w = $d->walk(function($n) {
+            return ($n instanceof Element) ? Node::WALK_ACCEPT : Node::WALK_REJECT;
+        });
+        $this->assertSame($d->documentElement, $w->current());
+        foreach ($w as $node);
+
+        // Accept element but ignore children, simple reject otherwise
+        $w = $d->walk(function($n) {
+            return ($n instanceof Element) ? Node::WALK_ACCEPT | Node::WALK_SKIP_CHILDREN : Node::WALK_REJECT;
+        });
+        $this->assertSame($d->documentElement, $w->current());
+        $this->assertNull($w->next());
+    }
+
+
+    /**
+     * @covers \MensBeam\HTML\DOM\ParentNode::walk
+     *
+     * @covers \MensBeam\HTML\DOM\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Document::createElement
+     * @covers \MensBeam\HTML\DOM\DOMException::__construct
+     * @covers \MensBeam\HTML\DOM\DOMImplementation::__construct
+     * @covers \MensBeam\HTML\DOM\Element::__construct
+     * @covers \MensBeam\HTML\DOM\Node::__construct
+     * @covers \MensBeam\HTML\DOM\Node::appendChild
+     * @covers \MensBeam\HTML\DOM\Node::getInnerDocument
+     * @covers \MensBeam\HTML\DOM\Node::getInnerNode
+     * @covers \MensBeam\HTML\DOM\Node::getRootNode
+     * @covers \MensBeam\HTML\DOM\Node::postInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionBugFixes
+     * @covers \MensBeam\HTML\DOM\Node::preInsertionValidity
+     * @covers \MensBeam\HTML\DOM\Inner\Document::__construct
+     * @covers \MensBeam\HTML\DOM\Inner\Document::getWrapperNode
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::get
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::has
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::key
+     * @covers \MensBeam\HTML\DOM\Inner\NodeCache::set
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::createFromProtectedConstructor
+     * @covers \MensBeam\HTML\DOM\Inner\Reflection::getProtectedProperty
+     */
+    public function testMethod_walk__errors(): void {
+        $this->expectException(DOMException::class);
+        $this->expectExceptionCode(DOMException::SYNTAX_ERROR);
+        $d = new Document();
+        $d->appendChild($d->createElement('html'));
+        $w = $d->walk(function($n) {
+            return 2112;
+        });
+        $w->current();
+    }
+
+
+    public function testProperty_childElementCount(): void {
+        $d = new Document('<!DOCTYPE html><html><body><div>ook</div><div id="eek">eek</div></body></html>');
+        $this->assertEquals(2, $d->body->childElementCount);
+    }
+
+
+    public function testProperty_children(): void {
+        $d = new Document('<!DOCTYPE html><html><body><div>ook</div><div id="eek">eek</div></body></html>');
+        $this->assertEquals(2, $d->body->children->length);
+    }
+
+
+    public function testProperty_firstElementChild(): void {
+        $d = new Document('<!DOCTYPE html><html><body>ook<div id="ook">ook</div><div id="eek">eek</div></body></html>');
+        $body = $d->body;
+        $this->assertSame($d->getElementById('ook'), $body->firstElementChild);
+        $this->assertNull($d->getElementById('eek')->firstElementChild);
+    }
+
+
+    public function testProperty_lastElementChild(): void {
+        $d = new Document('<!DOCTYPE html><html><body>ook<div id="ook">ook</div><div id="eek">eek</div><div id="ack">ack</div></body></html>');
+        $body = $d->body;
+        $this->assertSame($d->getElementById('ack'), $body->lastElementChild);
+        $this->assertNull($d->getElementById('eek')->lastElementChild);
+    }
 }
\ No newline at end of file
diff --git a/tests/phpunit.dist.xml b/tests/phpunit.dist.xml
index 7d6d314..1917f6f 100644
--- a/tests/phpunit.dist.xml
+++ b/tests/phpunit.dist.xml
@@ -18,6 +18,7 @@
     <testsuite name="DOM">
       <file>cases/TestAttr.php</file>
       <file>cases/TestCharacterData.php</file>
+      <file>cases/TestChildNode.php</file>
       <file>cases/TestDocument.php</file>
       <file>cases/TestDocumentOrElement.php</file>
       <file>cases/TestDOMImplementation.php</file>