xmldom allows multiple root nodes in a DOM

@@ -158,14 +158,14 @@ NodeList.prototype = {
 	 * The number of nodes in the list. The range of valid child node indices is 0 to length-1 inclusive.
 	 * @standard level1
 	 */
-	length:0, 
+	length:0,
 	/**
 	 * Returns the indexth item in the collection. If index is greater than or equal to the number of nodes in the list, this returns null.
 	 * @standard level1
-	 * @param index  unsigned long 
+	 * @param index  unsigned long
 	 *   Index into the collection.
 	 * @return Node
-	 * 	The node at the indexth position in the NodeList, or null if that is not a valid index. 
+	 * 	The node at the indexth position in the NodeList, or null if that is not a valid index.
 	 */
 	item: function(index) {
 		return this[index] || null;
@@ -175,7 +175,31 @@ NodeList.prototype = {
 			serializeToString(this[i],buf,isHTML,nodeFilter);
 		}
 		return buf.join('');
-	}
+	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node | undefined}
+	 */
+	find: function (predicate) {
+		return Array.prototype.find.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node[]}
+	 */
+	filter: function (predicate) {
+		return Array.prototype.filter.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {Node} item
+	 * @returns {number}
+	 */
+	indexOf: function (item) {
+		return Array.prototype.indexOf.call(this, item);
+	},
 };
 
 function LiveNodeList(node,refresh){
@@ -209,7 +233,7 @@ _extends(LiveNodeList,NodeList);
  * but this is simply to allow convenient enumeration of the contents of a NamedNodeMap,
  * and does not imply that the DOM specifies an order to these Nodes.
  * NamedNodeMap objects in the DOM are live.
- * used for attributes or DocumentType entities 
+ * used for attributes or DocumentType entities
  */
 function NamedNodeMap() {
 };
@@ -253,7 +277,7 @@ function _removeNamedNode(el,list,attr){
 			}
 		}
 	}else{
-		throw DOMException(NOT_FOUND_ERR,new Error(el.tagName+'@'+attr))
+		throw new DOMException(NOT_FOUND_ERR,new Error(el.tagName+'@'+attr))
 	}
 }
 NamedNodeMap.prototype = {
@@ -298,10 +322,10 @@ NamedNodeMap.prototype = {
 		var attr = this.getNamedItem(key);
 		_removeNamedNode(this._ownerElement,this,attr);
 		return attr;
-		
-		
+
+
 	},// raises: NOT_FOUND_ERR,NO_MODIFICATION_ALLOWED_ERR
-	
+
 	//for level2
 	removeNamedItemNS:function(namespaceURI,localName){
 		var attr = this.getNamedItemNS(namespaceURI,localName);
@@ -447,10 +471,10 @@ Node.prototype = {
 	prefix : null,
 	localName : null,
 	// Modified in DOM Level 2:
-	insertBefore:function(newChild, refChild){//raises 
+	insertBefore:function(newChild, refChild){//raises
 		return _insertBefore(this,newChild,refChild);
 	},
-	replaceChild:function(newChild, oldChild){//raises 
+	replaceChild:function(newChild, oldChild){//raises
 		this.insertBefore(newChild,oldChild);
 		if(oldChild){
 			this.removeChild(oldChild);
@@ -656,48 +680,177 @@ function _removeChild (parentNode, child) {
 	_onUpdateChild(parentNode.ownerDocument, parentNode);
 	return child;
 }
+
+/**
+ * Returns `true` if `node` can be a parent for insertion.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasValidParentNodeType(node) {
+	return (
+		node &&
+		(node.nodeType === Node.DOCUMENT_NODE || node.nodeType === Node.DOCUMENT_FRAGMENT_NODE || node.nodeType === Node.ELEMENT_NODE)
+	);
+}
+
+/**
+ * Returns `true` if `node` can be inserted according to it's `nodeType`.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasInsertableNodeType(node) {
+	return (
+		node &&
+		(isElementNode(node) ||
+			isTextNode(node) ||
+			isDocTypeNode(node) ||
+			node.nodeType === Node.DOCUMENT_FRAGMENT_NODE ||
+			node.nodeType === Node.COMMENT_NODE ||
+			node.nodeType === Node.PROCESSING_INSTRUCTION_NODE)
+	);
+}
+
+/**
+ * Returns true if `node` is a DOCTYPE node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isDocTypeNode(node) {
+	return node && node.nodeType === Node.DOCUMENT_TYPE_NODE;
+}
+
+/**
+ * Returns true if the node is an element
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isElementNode(node) {
+	return node && node.nodeType === Node.ELEMENT_NODE;
+}
+/**
+ * Returns true if `node` is a text node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isTextNode(node) {
+	return node && node.nodeType === Node.TEXT_NODE;
+}
+
+/**
+ * Check if en element node can be inserted before `child`, or at the end if child is falsy,
+ * according to the presence and position of a doctype node on the same level.
+ *
+ * @param {Document} doc The document node
+ * @param {Node} child the node that would become the nextSibling if the element would be inserted
+ * @returns {boolean} `true` if an element can be inserted before child
+ * @private
+ * https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
+ */
+function isElementInsertionPossible(doc, child) {
+	var parentChildNodes = doc.childNodes || [];
+	if (parentChildNodes.find(isElementNode) || isDocTypeNode(child)) {
+		return false;
+	}
+	var docTypeNode = parentChildNodes.find(isDocTypeNode);
+	return !(child && docTypeNode && parentChildNodes.indexOf(docTypeNode) > parentChildNodes.indexOf(child));
+}
 /**
- * preformance key(refChild == null)
+ * @private
+ * @param {Node} parent the parent node to insert `node` into
+ * @param {Node} node the node to insert
+ * @param {Node=} child the node that should become the `nextSibling` of `node`
+ * @returns {Node}
+ * @throws DOMException for several node combinations that would create a DOM that is not well-formed.
+ * @throws DOMException if `child` is provided but is not a child of `parent`.
+ * @see https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
  */
-function _insertBefore(parentNode,newChild,nextChild){
-	var cp = newChild.parentNode;
+function _insertBefore(parent, node, child) {
+	if (!hasValidParentNodeType(parent)) {
+		throw new DOMException(HIERARCHY_REQUEST_ERR, 'Unexpected parent node type ' + parent.nodeType);
+	}
+	if (child && child.parentNode !== parent) {
+		throw new DOMException(NOT_FOUND_ERR, 'child not in parent');
+	}
+	if (
+		!hasInsertableNodeType(node) ||
+		// the sax parser currently adds top level text nodes, this will be fixed in 0.9.0
+		// || (node.nodeType === Node.TEXT_NODE && parent.nodeType === Node.DOCUMENT_NODE)
+		(isDocTypeNode(node) && parent.nodeType !== Node.DOCUMENT_NODE)
+	) {
+		throw new DOMException(
+			HIERARCHY_REQUEST_ERR,
+			'Unexpected node type ' + node.nodeType + ' for parent node type ' + parent.nodeType
+		);
+	}
+	var parentChildNodes = parent.childNodes || [];
+	var nodeChildNodes = node.childNodes || [];
+	if (parent.nodeType === Node.DOCUMENT_NODE) {
+		if (node.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
+			let nodeChildElements = nodeChildNodes.filter(isElementNode);
+			if (nodeChildElements.length > 1 || nodeChildNodes.find(isTextNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'More than one element or text in fragment');
+			}
+			if (nodeChildElements.length === 1 && !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Element in fragment can not be inserted before doctype');
+			}
+		}
+		if (isElementNode(node)) {
+			if (parentChildNodes.find(isElementNode) || !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one element can be added and only after doctype');
+			}
+		}
+		if (isDocTypeNode(node)) {
+			if (parentChildNodes.find(isDocTypeNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one doctype is allowed');
+			}
+			let parentElementChild = parentChildNodes.find(isElementNode);
+			if (child && parentChildNodes.indexOf(parentElementChild) < parentChildNodes.indexOf(child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can only be inserted before an element');
+			}
+			if (!child && parentElementChild) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can not be appended since element is present');
+			}
+		}
+	}
+
+	var cp = node.parentNode;
 	if(cp){
-		cp.removeChild(newChild);//remove and update
+		cp.removeChild(node);//remove and update
 	}
-	if(newChild.nodeType === DOCUMENT_FRAGMENT_NODE){
-		var newFirst = newChild.firstChild;
+	if(node.nodeType === DOCUMENT_FRAGMENT_NODE){
+		var newFirst = node.firstChild;
 		if (newFirst == null) {
-			return newChild;
+			return node;
 		}
-		var newLast = newChild.lastChild;
+		var newLast = node.lastChild;
 	}else{
-		newFirst = newLast = newChild;
+		newFirst = newLast = node;
 	}
-	var pre = nextChild ? nextChild.previousSibling : parentNode.lastChild;
+	var pre = child ? child.previousSibling : parent.lastChild;
 
 	newFirst.previousSibling = pre;
-	newLast.nextSibling = nextChild;
-	
-	
+	newLast.nextSibling = child;
+
+
 	if(pre){
 		pre.nextSibling = newFirst;
 	}else{
-		parentNode.firstChild = newFirst;
+		parent.firstChild = newFirst;
 	}
-	if(nextChild == null){
-		parentNode.lastChild = newLast;
+	if(child == null){
+		parent.lastChild = newLast;
 	}else{
-		nextChild.previousSibling = newLast;
+		child.previousSibling = newLast;
 	}
 	do{
-		newFirst.parentNode = parentNode;
+		newFirst.parentNode = parent;
 	}while(newFirst !== newLast && (newFirst= newFirst.nextSibling))
-	_onUpdateChild(parentNode.ownerDocument||parentNode,parentNode);
-	//console.log(parentNode.lastChild.nextSibling == null)
-	if (newChild.nodeType == DOCUMENT_FRAGMENT_NODE) {
-		newChild.firstChild = newChild.lastChild = null;
+	_onUpdateChild(parent.ownerDocument||parent, parent);
+	//console.log(parent.lastChild.nextSibling == null)
+	if (node.nodeType == DOCUMENT_FRAGMENT_NODE) {
+		node.firstChild = node.lastChild = null;
 	}
-	return newChild;
+	return node;
 }
 
 /**
@@ -752,11 +905,13 @@ Document.prototype = {
 			}
 			return newChild;
 		}
-		if(this.documentElement == null && newChild.nodeType == ELEMENT_NODE){
+		_insertBefore(this, newChild, refChild);
+		newChild.ownerDocument = this;
+		if (this.documentElement === null && newChild.nodeType === ELEMENT_NODE) {
 			this.documentElement = newChild;
 		}
 
-		return _insertBefore(this,newChild,refChild),(newChild.ownerDocument = this),newChild;
+		return newChild;
 	},
 	removeChild :  function(oldChild){
 		if(this.documentElement == oldChild){
@@ -950,7 +1105,7 @@ Element.prototype = {
 		var attr = this.getAttributeNode(name)
 		attr && this.removeAttributeNode(attr);
 	},
-	
+
 	//four real opeartion method
 	appendChild:function(newChild){
 		if(newChild.nodeType === DOCUMENT_FRAGMENT_NODE){
@@ -974,7 +1129,7 @@ Element.prototype = {
 		var old = this.getAttributeNodeNS(namespaceURI, localName);
 		old && this.removeAttributeNode(old);
 	},
-	
+
 	hasAttributeNS : function(namespaceURI, localName){
 		return this.getAttributeNodeNS(namespaceURI, localName)!=null;
 	},
@@ -990,7 +1145,7 @@ Element.prototype = {
 	getAttributeNodeNS : function(namespaceURI, localName){
 		return this.attributes.getNamedItemNS(namespaceURI, localName);
 	},
-	
+
 	getElementsByTagName : function(tagName){
 		return new LiveNodeList(this,function(base){
 			var ls = [];
@@ -1011,7 +1166,7 @@ Element.prototype = {
 				}
 			});
 			return ls;
-			
+
 		});
 	}
 };
@@ -1040,7 +1195,7 @@ CharacterData.prototype = {
 	},
 	insertData: function(offset,text) {
 		this.replaceData(offset,0,text);
-	
+
 	},
 	appendChild:function(newChild){
 		throw new Error(ExceptionMessage[HIERARCHY_REQUEST_ERR])
@@ -1134,7 +1289,7 @@ function nodeSerializeToString(isHtml,nodeFilter){
 	var refNode = this.nodeType == 9 && this.documentElement || this;
 	var prefix = refNode.prefix;
 	var uri = refNode.namespaceURI;
-	
+
 	if(uri && prefix == null){
 		//console.log(prefix)
 		var prefix = refNode.lookupPrefix(uri);
@@ -1167,8 +1322,8 @@ function needNamespaceDefine(node, isHTML, visibleNamespaces) {
 	if (prefix === "xml" && uri === NAMESPACE.XML || uri === NAMESPACE.XMLNS) {
 		return false;
 	}
-	
-	var i = visibleNamespaces.length 
+
+	var i = visibleNamespaces.length
 	while (i--) {
 		var ns = visibleNamespaces[i];
 		// get namespace prefix
@@ -1219,7 +1374,7 @@ function serializeToString(node,buf,isHTML,nodeFilter,visibleNamespaces){
 		var len = attrs.length;
 		var child = node.firstChild;
 		var nodeName = node.tagName;
-		
+
 		isHTML = NAMESPACE.isHTML(node.namespaceURI) || isHTML
 
 		var prefixedNodeName = nodeName
@@ -1278,14 +1433,14 @@ function serializeToString(node,buf,isHTML,nodeFilter,visibleNamespaces){
 			serializeToString(attr,buf,isHTML,nodeFilter,visibleNamespaces);
 		}
 
-		// add namespace for current node		
+		// add namespace for current node
 		if (nodeName === prefixedNodeName && needNamespaceDefine(node, isHTML, visibleNamespaces)) {
 			var prefix = node.prefix||'';
 			var uri = node.namespaceURI;
 			addSerializedAttribute(buf, prefix ? 'xmlns:' + prefix : "xmlns", uri);
 			visibleNamespaces.push({ prefix: prefix, namespace:uri });
 		}
-		
+
 		if(child || isHTML && !/^(?:meta|link|img|br|hr|input)$/i.test(nodeName)){
 			buf.push('>');
 			//if is cdata child node
@@ -1500,7 +1655,7 @@ try{
 				}
 			}
 		})
-		
+
 		function getTextContent(node){
 			switch(node.nodeType){
 			case ELEMENT_NODE:

@@ -1,7 +1,7 @@
-'use strict'
+'use strict';
 
-const { getTestParser } = require('../get-test-parser')
-const { DOMImplementation } = require('../../lib/dom')
+const { getTestParser } = require('../get-test-parser');
+const { DOMImplementation, DOMException } = require('../../lib/dom');
 
 const INPUT = (first = '', second = '', third = '', fourth = '') => `
 <html >
@@ -99,4 +99,68 @@ describe('Document.prototype', () => {
 			expect(doc.firstChild === doctype).toBe(true)
 		})
 	})
+	describe('insertBefore', () => {
+		it('should insert the first element and set `documentElement`', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			expect(doc.childNodes).toHaveLength(0);
+			expect(doc.documentElement).toBeNull();
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(doc.childNodes.item(0)).toBe(root);
+		});
+		it('should prevent inserting a second element', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const second = doc.createElement('second');
+			doc.insertBefore(root);
+			expect(() => doc.insertBefore(second)).toThrow(DOMException);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting an element before a doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			const root = doc.createElement('root');
+			expect(() => doc.insertBefore(root, doctype)).toThrow(DOMException);
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(1);
+			expect(root.parentNode).toBeNull();
+		});
+		it('should prevent inserting a second doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doctype2 = impl.createDocumentType('DT2');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(() => doc.insertBefore(doctype2)).toThrow(DOMException);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting a doctype after an element', () => {
+			const impl = new DOMImplementation();
+			const doc = impl.createDocument(null, '');
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			const doctype = impl.createDocumentType('DT');
+			expect(doc.childNodes).toHaveLength(1);
+
+			expect(() => doc.insertBefore(doctype)).toThrow(DOMException);
+
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting before an child which is not a child of parent', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const withoutParent = doc.createElement('second');
+
+			expect(() => doc.insertBefore(root, withoutParent)).toThrow(DOMException);
+
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(0);
+			expect(root.parentNode).toBeNull();
+		});
+	});
 })

@@ -41,10 +41,10 @@ describe('XML Node Parse', () => {
 
 	it('sibling closing tag with whitespace', () => {
 		const actual = new DOMParser()
-			.parseFromString(`<book></book ><title>Harry Potter</title>`, 'text/xml')
-			.toString()
-		expect(actual).toBe(`<book/><title>Harry Potter</title>`)
-	})
+			.parseFromString(`<xml><book></book ><title>Harry Potter</title></xml>`, 'text/xml')
+			.toString();
+		expect(actual).toBe(`<xml><book/><title>Harry Potter</title></xml>`);
+	});
 
 	describe('simple attributes', () => {
 		describe('nothing special', () => {

@@ -315,14 +315,22 @@ Object {
 exports[`xmltest/not-wellformed standalone should match 040.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc&gt;",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
 exports[`xmltest/not-wellformed standalone should match 041.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc&gt;",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
@@ -342,7 +350,12 @@ Illegal data
 
 exports[`xmltest/not-wellformed standalone should match 044.xml with snapshot 1`] = `
 Object {
-  "actual": "<doc/><doc/>",
+  "actual": "<doc/>&lt;doc/&gt;
+",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:1,col:7]",
+  ],
 }
 `;
 

@@ -180,6 +180,30 @@ NodeList.prototype = {
 		}
 		return buf.join('');
 	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node | undefined}
+	 */
+	find: function (predicate) {
+		return Array.prototype.find.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node[]}
+	 */
+	filter: function (predicate) {
+		return Array.prototype.filter.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {Node} item
+	 * @returns {number}
+	 */
+	indexOf: function (item) {
+		return Array.prototype.indexOf.call(this, item);
+	},
 };
 
 function LiveNodeList(node, refresh) {
@@ -455,7 +479,7 @@ DOMImplementation.prototype = {
 		doc.childNodes = new NodeList();
 		if (title !== false) {
 			doc.doctype = this.createDocumentType('html');
-			doc.doctype.ownerDocument = this;
+			doc.doctype.ownerDocument = doc;
 			doc.appendChild(doc.doctype);
 			var htmlNode = doc.createElement('html');
 			doc.appendChild(htmlNode);
@@ -636,6 +660,7 @@ function _visitNode(node, callback) {
  */
 function Document(options) {
 	var opt = options || {};
+	this.ownerDocument = this;
 	/**
 	 * The mime type of the document is determined at creation time and can not be modified.
 	 *
@@ -739,47 +764,176 @@ function _removeChild(parentNode, child) {
 	_onUpdateChild(parentNode.ownerDocument, parentNode);
 	return child;
 }
+
+/**
+ * Returns `true` if `node` can be a parent for insertion.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasValidParentNodeType(node) {
+	return (
+		node &&
+		(node.nodeType === Node.DOCUMENT_NODE || node.nodeType === Node.DOCUMENT_FRAGMENT_NODE || node.nodeType === Node.ELEMENT_NODE)
+	);
+}
+
+/**
+ * Returns `true` if `node` can be inserted according to it's `nodeType`.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasInsertableNodeType(node) {
+	return (
+		node &&
+		(isElementNode(node) ||
+			isTextNode(node) ||
+			isDocTypeNode(node) ||
+			node.nodeType === Node.DOCUMENT_FRAGMENT_NODE ||
+			node.nodeType === Node.COMMENT_NODE ||
+			node.nodeType === Node.PROCESSING_INSTRUCTION_NODE)
+	);
+}
+
 /**
- * preformance key(refChild == null)
+ * Returns true if `node` is a DOCTYPE node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isDocTypeNode(node) {
+	return node && node.nodeType === Node.DOCUMENT_TYPE_NODE;
+}
+
+/**
+ * Returns true if the node is an element
+ * @param {Node} node
+ * @returns {boolean}
  */
-function _insertBefore(parentNode, newChild, nextChild) {
-	var cp = newChild.parentNode;
+function isElementNode(node) {
+	return node && node.nodeType === Node.ELEMENT_NODE;
+}
+/**
+ * Returns true if `node` is a text node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isTextNode(node) {
+	return node && node.nodeType === Node.TEXT_NODE;
+}
+
+/**
+ * Check if en element node can be inserted before `child`, or at the end if child is falsy,
+ * according to the presence and position of a doctype node on the same level.
+ *
+ * @param {Document} doc The document node
+ * @param {Node} child the node that would become the nextSibling if the element would be inserted
+ * @returns {boolean} `true` if an element can be inserted before child
+ * @private
+ * https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
+ */
+function isElementInsertionPossible(doc, child) {
+	var parentChildNodes = doc.childNodes || [];
+	if (parentChildNodes.find(isElementNode) || isDocTypeNode(child)) {
+		return false;
+	}
+	var docTypeNode = parentChildNodes.find(isDocTypeNode);
+	return !(child && docTypeNode && parentChildNodes.indexOf(docTypeNode) > parentChildNodes.indexOf(child));
+}
+/**
+ * @private
+ * @param {Node} parent the parent node to insert `node` into
+ * @param {Node} node the node to insert
+ * @param {Node=} child the node that should become the `nextSibling` of `node`
+ * @returns {Node}
+ * @throws DOMException for several node combinations that would create a DOM that is not well-formed.
+ * @throws DOMException if `child` is provided but is not a child of `parent`.
+ * @see https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
+ */
+function _insertBefore(parent, node, child) {
+	if (!hasValidParentNodeType(parent)) {
+		throw new DOMException(HIERARCHY_REQUEST_ERR, 'Unexpected parent node type ' + parent.nodeType);
+	}
+	if (child && child.parentNode !== parent) {
+		throw new DOMException(NOT_FOUND_ERR, 'child not in parent');
+	}
+	if (
+		!hasInsertableNodeType(node) ||
+		// the sax parser currently adds top level text nodes, this will be fixed in 0.9.0
+		// || (node.nodeType === Node.TEXT_NODE && parent.nodeType === Node.DOCUMENT_NODE)
+		(isDocTypeNode(node) && parent.nodeType !== Node.DOCUMENT_NODE)
+	) {
+		throw new DOMException(
+			HIERARCHY_REQUEST_ERR,
+			'Unexpected node type ' + node.nodeType + ' for parent node type ' + parent.nodeType
+		);
+	}
+	var parentChildNodes = parent.childNodes || [];
+	var nodeChildNodes = node.childNodes || [];
+	if (parent.nodeType === Node.DOCUMENT_NODE) {
+		if (node.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
+			let nodeChildElements = nodeChildNodes.filter(isElementNode);
+			if (nodeChildElements.length > 1 || nodeChildNodes.find(isTextNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'More than one element or text in fragment');
+			}
+			if (nodeChildElements.length === 1 && !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Element in fragment can not be inserted before doctype');
+			}
+		}
+		if (isElementNode(node)) {
+			if (parentChildNodes.find(isElementNode) || !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one element can be added and only after doctype');
+			}
+		}
+		if (isDocTypeNode(node)) {
+			if (parentChildNodes.find(isDocTypeNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one doctype is allowed');
+			}
+			let parentElementChild = parentChildNodes.find(isElementNode);
+			if (child && parentChildNodes.indexOf(parentElementChild) < parentChildNodes.indexOf(child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can only be inserted before an element');
+			}
+			if (!child && parentElementChild) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can not be appended since element is present');
+			}
+		}
+	}
+
+	var cp = node.parentNode;
 	if (cp) {
-		cp.removeChild(newChild); //remove and update
+		cp.removeChild(node); //remove and update
 	}
-	if (newChild.nodeType === DOCUMENT_FRAGMENT_NODE) {
-		var newFirst = newChild.firstChild;
+	if (node.nodeType === DOCUMENT_FRAGMENT_NODE) {
+		var newFirst = node.firstChild;
 		if (newFirst == null) {
-			return newChild;
+			return node;
 		}
-		var newLast = newChild.lastChild;
+		var newLast = node.lastChild;
 	} else {
-		newFirst = newLast = newChild;
+		newFirst = newLast = node;
 	}
-	var pre = nextChild ? nextChild.previousSibling : parentNode.lastChild;
+	var pre = child ? child.previousSibling : parent.lastChild;
 
 	newFirst.previousSibling = pre;
-	newLast.nextSibling = nextChild;
+	newLast.nextSibling = child;
 
 	if (pre) {
 		pre.nextSibling = newFirst;
 	} else {
-		parentNode.firstChild = newFirst;
+		parent.firstChild = newFirst;
 	}
-	if (nextChild == null) {
-		parentNode.lastChild = newLast;
+	if (child == null) {
+		parent.lastChild = newLast;
 	} else {
-		nextChild.previousSibling = newLast;
+		child.previousSibling = newLast;
 	}
 	do {
-		newFirst.parentNode = parentNode;
+		newFirst.parentNode = parent;
 	} while (newFirst !== newLast && (newFirst = newFirst.nextSibling));
-	_onUpdateChild(parentNode.ownerDocument || parentNode, parentNode);
-	//console.log(parentNode.lastChild.nextSibling == null)
-	if (newChild.nodeType == DOCUMENT_FRAGMENT_NODE) {
-		newChild.firstChild = newChild.lastChild = null;
+	_onUpdateChild(parent.ownerDocument || parent, parent);
+	//console.log(parent.lastChild.nextSibling == null)
+	if (node.nodeType == DOCUMENT_FRAGMENT_NODE) {
+		node.firstChild = node.lastChild = null;
 	}
-	return newChild;
+	return node;
 }
 
 /**
@@ -840,11 +994,13 @@ Document.prototype = {
 			}
 			return newChild;
 		}
-		if (this.documentElement == null && newChild.nodeType == ELEMENT_NODE) {
+		_insertBefore(this, newChild, refChild);
+		newChild.ownerDocument = this;
+		if (this.documentElement === null && newChild.nodeType === ELEMENT_NODE) {
 			this.documentElement = newChild;
 		}
 
-		return _insertBefore(this, newChild, refChild), (newChild.ownerDocument = this), newChild;
+		return newChild;
 	},
 	removeChild: function (oldChild) {
 		if (this.documentElement == oldChild) {

@@ -1,16 +1,16 @@
 'use strict';
 
 const { getTestParser } = require('../get-test-parser');
-const { DOMImplementation } = require('../../lib/dom');
+const { DOMImplementation, DOMException } = require('../../lib/dom');
 const { NAMESPACE } = require('../../lib/conventions');
 
 const INPUT = (first = '', second = '', third = '', fourth = '') => `
 <html >
-	<body id="body">
-		<p id="p1" class=" quote first   odd ${first} ">Lorem ipsum</p>
-		<p id="p2" class=" quote second  even ${second} ">Lorem ipsum</p>
-		<p id="p3" class=" quote third   odd ${third} ">Lorem ipsum</p>
-		<p id="p4" class=" quote fourth  even ${fourth} ">Lorem ipsum</p>
+	<body id='body'>
+		<p id='p1' class=' quote first   odd ${first} '>Lorem ipsum</p>
+		<p id='p2' class=' quote second  even ${second} '>Lorem ipsum</p>
+		<p id='p3' class=' quote third   odd ${third} '>Lorem ipsum</p>
+		<p id='p4' class=' quote fourth  even ${fourth} '>Lorem ipsum</p>
 	</body>
 </html>
 `;
@@ -166,4 +166,68 @@ describe('Document.prototype', () => {
 			expect(attr.nodeName).toBe('name');
 		});
 	});
+	describe('insertBefore', () => {
+		it('should insert the first element and set `documentElement`', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			expect(doc.childNodes).toHaveLength(0);
+			expect(doc.documentElement).toBeNull();
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(doc.childNodes.item(0)).toBe(root);
+		});
+		it('should prevent inserting a second element', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const second = doc.createElement('second');
+			doc.insertBefore(root);
+			expect(() => doc.insertBefore(second)).toThrow(DOMException);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting an element before a doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			const root = doc.createElement('root');
+			expect(() => doc.insertBefore(root, doctype)).toThrow(DOMException);
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(1);
+			expect(root.parentNode).toBeNull();
+		});
+		it('should prevent inserting a second doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doctype2 = impl.createDocumentType('DT2');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(() => doc.insertBefore(doctype2)).toThrow(DOMException);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting a doctype after an element', () => {
+			const impl = new DOMImplementation();
+			const doc = impl.createDocument(null, '');
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			const doctype = impl.createDocumentType('DT');
+			expect(doc.childNodes).toHaveLength(1);
+
+			expect(() => doc.insertBefore(doctype)).toThrow(DOMException);
+
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting before an child which is not a child of parent', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const withoutParent = doc.createElement('second');
+
+			expect(() => doc.insertBefore(root, withoutParent)).toThrow(DOMException);
+
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(0);
+			expect(root.parentNode).toBeNull();
+		});
+	});
 });

@@ -29,6 +29,7 @@ describe('DOMImplementation', () => {
 
 			expect(doc.nodeType).toBe(Node.DOCUMENT_NODE);
 			expect(doc.implementation).toBe(impl);
+			expect(doc.ownerDocument).toBe(doc);
 			expect(doc.doctype).toBe(null);
 			expect(doc.childNodes).toBeInstanceOf(NodeList);
 			expect(doc.documentElement).toBe(null);
@@ -193,6 +194,7 @@ describe('DOMImplementation', () => {
 			expect(doc.childNodes.length).toBe(0);
 			expect(doc.doctype).toBeNull();
 			expect(doc.documentElement).toBeNull();
+			expect(doc.ownerDocument).toBe(doc);
 		});
 		it('should create an HTML document with minimum specified elements when title not provided', () => {
 			const impl = new DOMImplementation();

@@ -35,8 +35,8 @@ describe('XML Node Parse', () => {
 	});
 
 	it('sibling closing tag with whitespace', () => {
-		const actual = new DOMParser().parseFromString(`<book></book ><title>Harry Potter</title>`, 'text/xml').toString();
-		expect(actual).toBe(`<book/><title>Harry Potter</title>`);
+		const actual = new DOMParser().parseFromString(`<xml><book></book ><title>Harry Potter</title></xml>`, 'text/xml').toString();
+		expect(actual).toBe(`<xml><book/><title>Harry Potter</title></xml>`);
 	});
 
 	describe('simple attributes', () => {

@@ -315,14 +315,22 @@ Object {
 exports[`xmltest/not-wellformed standalone should match 040.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc&gt;",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
 exports[`xmltest/not-wellformed standalone should match 041.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc&gt;",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
@@ -342,7 +350,12 @@ Illegal data
 
 exports[`xmltest/not-wellformed standalone should match 044.xml with snapshot 1`] = `
 Object {
-  "actual": "<doc/><doc/>",
+  "actual": "<doc/>&lt;doc/&gt;
+",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:1,col:7]",
+  ],
 }
 `;
 

@@ -158,14 +158,14 @@ NodeList.prototype = {
 	 * The number of nodes in the list. The range of valid child node indices is 0 to length-1 inclusive.
 	 * @standard level1
 	 */
-	length:0, 
+	length:0,
 	/**
 	 * Returns the indexth item in the collection. If index is greater than or equal to the number of nodes in the list, this returns null.
 	 * @standard level1
-	 * @param index  unsigned long 
+	 * @param index  unsigned long
 	 *   Index into the collection.
 	 * @return Node
-	 * 	The node at the indexth position in the NodeList, or null if that is not a valid index. 
+	 * 	The node at the indexth position in the NodeList, or null if that is not a valid index.
 	 */
 	item: function(index) {
 		return this[index] || null;
@@ -175,7 +175,31 @@ NodeList.prototype = {
 			serializeToString(this[i],buf,isHTML,nodeFilter);
 		}
 		return buf.join('');
-	}
+	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node | undefined}
+	 */
+	find: function (predicate) {
+		return Array.prototype.find.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {function (Node):boolean} predicate
+	 * @returns {Node[]}
+	 */
+	filter: function (predicate) {
+		return Array.prototype.filter.call(this, predicate);
+	},
+	/**
+	 * @private
+	 * @param {Node} item
+	 * @returns {number}
+	 */
+	indexOf: function (item) {
+		return Array.prototype.indexOf.call(this, item);
+	},
 };
 
 function LiveNodeList(node,refresh){
@@ -209,7 +233,7 @@ _extends(LiveNodeList,NodeList);
  * but this is simply to allow convenient enumeration of the contents of a NamedNodeMap,
  * and does not imply that the DOM specifies an order to these Nodes.
  * NamedNodeMap objects in the DOM are live.
- * used for attributes or DocumentType entities 
+ * used for attributes or DocumentType entities
  */
 function NamedNodeMap() {
 };
@@ -253,7 +277,7 @@ function _removeNamedNode(el,list,attr){
 			}
 		}
 	}else{
-		throw DOMException(NOT_FOUND_ERR,new Error(el.tagName+'@'+attr))
+		throw new DOMException(NOT_FOUND_ERR,new Error(el.tagName+'@'+attr))
 	}
 }
 NamedNodeMap.prototype = {
@@ -298,10 +322,10 @@ NamedNodeMap.prototype = {
 		var attr = this.getNamedItem(key);
 		_removeNamedNode(this._ownerElement,this,attr);
 		return attr;
-		
-		
+
+
 	},// raises: NOT_FOUND_ERR,NO_MODIFICATION_ALLOWED_ERR
-	
+
 	//for level2
 	removeNamedItemNS:function(namespaceURI,localName){
 		var attr = this.getNamedItemNS(namespaceURI,localName);
@@ -447,10 +471,10 @@ Node.prototype = {
 	prefix : null,
 	localName : null,
 	// Modified in DOM Level 2:
-	insertBefore:function(newChild, refChild){//raises 
+	insertBefore:function(newChild, refChild){//raises
 		return _insertBefore(this,newChild,refChild);
 	},
-	replaceChild:function(newChild, oldChild){//raises 
+	replaceChild:function(newChild, oldChild){//raises
 		this.insertBefore(newChild,oldChild);
 		if(oldChild){
 			this.removeChild(oldChild);
@@ -618,7 +642,7 @@ function _onUpdateChild(doc,el,newChild){
 /**
  * attributes;
  * children;
- * 
+ *
  * writeable properties:
  * nodeValue,Attr:value,CharacterData:data
  * prefix
@@ -639,48 +663,177 @@ function _removeChild(parentNode,child){
 	_onUpdateChild(parentNode.ownerDocument,parentNode);
 	return child;
 }
+
 /**
- * preformance key(refChild == null)
+ * Returns `true` if `node` can be a parent for insertion.
+ * @param {Node} node
+ * @returns {boolean}
  */
-function _insertBefore(parentNode,newChild,nextChild){
-	var cp = newChild.parentNode;
+function hasValidParentNodeType(node) {
+	return (
+		node &&
+		(node.nodeType === Node.DOCUMENT_NODE || node.nodeType === Node.DOCUMENT_FRAGMENT_NODE || node.nodeType === Node.ELEMENT_NODE)
+	);
+}
+
+/**
+ * Returns `true` if `node` can be inserted according to it's `nodeType`.
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function hasInsertableNodeType(node) {
+	return (
+		node &&
+		(isElementNode(node) ||
+			isTextNode(node) ||
+			isDocTypeNode(node) ||
+			node.nodeType === Node.DOCUMENT_FRAGMENT_NODE ||
+			node.nodeType === Node.COMMENT_NODE ||
+			node.nodeType === Node.PROCESSING_INSTRUCTION_NODE)
+	);
+}
+
+/**
+ * Returns true if `node` is a DOCTYPE node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isDocTypeNode(node) {
+	return node && node.nodeType === Node.DOCUMENT_TYPE_NODE;
+}
+
+/**
+ * Returns true if the node is an element
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isElementNode(node) {
+	return node && node.nodeType === Node.ELEMENT_NODE;
+}
+/**
+ * Returns true if `node` is a text node
+ * @param {Node} node
+ * @returns {boolean}
+ */
+function isTextNode(node) {
+	return node && node.nodeType === Node.TEXT_NODE;
+}
+
+/**
+ * Check if en element node can be inserted before `child`, or at the end if child is falsy,
+ * according to the presence and position of a doctype node on the same level.
+ *
+ * @param {Document} doc The document node
+ * @param {Node} child the node that would become the nextSibling if the element would be inserted
+ * @returns {boolean} `true` if an element can be inserted before child
+ * @private
+ * https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
+ */
+function isElementInsertionPossible(doc, child) {
+	var parentChildNodes = doc.childNodes || [];
+	if (parentChildNodes.find(isElementNode) || isDocTypeNode(child)) {
+		return false;
+	}
+	var docTypeNode = parentChildNodes.find(isDocTypeNode);
+	return !(child && docTypeNode && parentChildNodes.indexOf(docTypeNode) > parentChildNodes.indexOf(child));
+}
+/**
+ * @private
+ * @param {Node} parent the parent node to insert `node` into
+ * @param {Node} node the node to insert
+ * @param {Node=} child the node that should become the `nextSibling` of `node`
+ * @returns {Node}
+ * @throws DOMException for several node combinations that would create a DOM that is not well-formed.
+ * @throws DOMException if `child` is provided but is not a child of `parent`.
+ * @see https://dom.spec.whatwg.org/#concept-node-ensure-pre-insertion-validity
+ */
+function _insertBefore(parent, node, child) {
+	if (!hasValidParentNodeType(parent)) {
+		throw new DOMException(HIERARCHY_REQUEST_ERR, 'Unexpected parent node type ' + parent.nodeType);
+	}
+	if (child && child.parentNode !== parent) {
+		throw new DOMException(NOT_FOUND_ERR, 'child not in parent');
+	}
+	if (
+		!hasInsertableNodeType(node) ||
+		// the sax parser currently adds top level text nodes, this will be fixed in 0.9.0
+		// || (node.nodeType === Node.TEXT_NODE && parent.nodeType === Node.DOCUMENT_NODE)
+		(isDocTypeNode(node) && parent.nodeType !== Node.DOCUMENT_NODE)
+	) {
+		throw new DOMException(
+			HIERARCHY_REQUEST_ERR,
+			'Unexpected node type ' + node.nodeType + ' for parent node type ' + parent.nodeType
+		);
+	}
+	var parentChildNodes = parent.childNodes || [];
+	var nodeChildNodes = node.childNodes || [];
+	if (parent.nodeType === Node.DOCUMENT_NODE) {
+		if (node.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
+			let nodeChildElements = nodeChildNodes.filter(isElementNode);
+			if (nodeChildElements.length > 1 || nodeChildNodes.find(isTextNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'More than one element or text in fragment');
+			}
+			if (nodeChildElements.length === 1 && !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Element in fragment can not be inserted before doctype');
+			}
+		}
+		if (isElementNode(node)) {
+			if (parentChildNodes.find(isElementNode) || !isElementInsertionPossible(parent, child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one element can be added and only after doctype');
+			}
+		}
+		if (isDocTypeNode(node)) {
+			if (parentChildNodes.find(isDocTypeNode)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Only one doctype is allowed');
+			}
+			let parentElementChild = parentChildNodes.find(isElementNode);
+			if (child && parentChildNodes.indexOf(parentElementChild) < parentChildNodes.indexOf(child)) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can only be inserted before an element');
+			}
+			if (!child && parentElementChild) {
+				throw new DOMException(HIERARCHY_REQUEST_ERR, 'Doctype can not be appended since element is present');
+			}
+		}
+	}
+
+	var cp = node.parentNode;
 	if(cp){
-		cp.removeChild(newChild);//remove and update
+		cp.removeChild(node);//remove and update
 	}
-	if(newChild.nodeType === DOCUMENT_FRAGMENT_NODE){
-		var newFirst = newChild.firstChild;
+	if(node.nodeType === DOCUMENT_FRAGMENT_NODE){
+		var newFirst = node.firstChild;
 		if (newFirst == null) {
-			return newChild;
+			return node;
 		}
-		var newLast = newChild.lastChild;
+		var newLast = node.lastChild;
 	}else{
-		newFirst = newLast = newChild;
+		newFirst = newLast = node;
 	}
-	var pre = nextChild ? nextChild.previousSibling : parentNode.lastChild;
+	var pre = child ? child.previousSibling : parent.lastChild;
 
 	newFirst.previousSibling = pre;
-	newLast.nextSibling = nextChild;
-	
-	
+	newLast.nextSibling = child;
+
+
 	if(pre){
 		pre.nextSibling = newFirst;
 	}else{
-		parentNode.firstChild = newFirst;
+		parent.firstChild = newFirst;
 	}
-	if(nextChild == null){
-		parentNode.lastChild = newLast;
+	if(child == null){
+		parent.lastChild = newLast;
 	}else{
-		nextChild.previousSibling = newLast;
+		child.previousSibling = newLast;
 	}
 	do{
-		newFirst.parentNode = parentNode;
+		newFirst.parentNode = parent;
 	}while(newFirst !== newLast && (newFirst= newFirst.nextSibling))
-	_onUpdateChild(parentNode.ownerDocument||parentNode,parentNode);
-	//console.log(parentNode.lastChild.nextSibling == null)
-	if (newChild.nodeType == DOCUMENT_FRAGMENT_NODE) {
-		newChild.firstChild = newChild.lastChild = null;
+	_onUpdateChild(parent.ownerDocument||parent, parent);
+	//console.log(parent.lastChild.nextSibling == null)
+	if (node.nodeType == DOCUMENT_FRAGMENT_NODE) {
+		node.firstChild = node.lastChild = null;
 	}
-	return newChild;
+	return node;
 }
 function _appendSingleChild(parentNode,newChild){
 	var cp = newChild.parentNode;
@@ -703,6 +856,7 @@ function _appendSingleChild(parentNode,newChild){
 	return newChild;
 	//console.log("__aa",parentNode.lastChild.nextSibling == null)
 }
+
 Document.prototype = {
 	//implementation : null,
 	nodeName :  '#document',
@@ -727,11 +881,13 @@ Document.prototype = {
 			}
 			return newChild;
 		}
-		if(this.documentElement == null && newChild.nodeType == ELEMENT_NODE){
+		_insertBefore(this, newChild, refChild);
+		newChild.ownerDocument = this;
+		if (this.documentElement === null && newChild.nodeType === ELEMENT_NODE) {
 			this.documentElement = newChild;
 		}
 
-		return _insertBefore(this,newChild,refChild),(newChild.ownerDocument = this),newChild;
+		return newChild;
 	},
 	removeChild :  function(oldChild){
 		if(this.documentElement == oldChild){
@@ -925,7 +1081,7 @@ Element.prototype = {
 		var attr = this.getAttributeNode(name)
 		attr && this.removeAttributeNode(attr);
 	},
-	
+
 	//four real opeartion method
 	appendChild:function(newChild){
 		if(newChild.nodeType === DOCUMENT_FRAGMENT_NODE){
@@ -949,7 +1105,7 @@ Element.prototype = {
 		var old = this.getAttributeNodeNS(namespaceURI, localName);
 		old && this.removeAttributeNode(old);
 	},
-	
+
 	hasAttributeNS : function(namespaceURI, localName){
 		return this.getAttributeNodeNS(namespaceURI, localName)!=null;
 	},
@@ -965,7 +1121,7 @@ Element.prototype = {
 	getAttributeNodeNS : function(namespaceURI, localName){
 		return this.attributes.getNamedItemNS(namespaceURI, localName);
 	},
-	
+
 	getElementsByTagName : function(tagName){
 		return new LiveNodeList(this,function(base){
 			var ls = [];
@@ -986,7 +1142,7 @@ Element.prototype = {
 				}
 			});
 			return ls;
-			
+
 		});
 	}
 };
@@ -1015,7 +1171,7 @@ CharacterData.prototype = {
 	},
 	insertData: function(offset,text) {
 		this.replaceData(offset,0,text);
-	
+
 	},
 	appendChild:function(newChild){
 		throw new Error(ExceptionMessage[HIERARCHY_REQUEST_ERR])
@@ -1109,7 +1265,7 @@ function nodeSerializeToString(isHtml,nodeFilter){
 	var refNode = this.nodeType == 9 && this.documentElement || this;
 	var prefix = refNode.prefix;
 	var uri = refNode.namespaceURI;
-	
+
 	if(uri && prefix == null){
 		//console.log(prefix)
 		var prefix = refNode.lookupPrefix(uri);
@@ -1142,8 +1298,8 @@ function needNamespaceDefine(node, isHTML, visibleNamespaces) {
 	if (prefix === "xml" && uri === NAMESPACE.XML || uri === NAMESPACE.XMLNS) {
 		return false;
 	}
-	
-	var i = visibleNamespaces.length 
+
+	var i = visibleNamespaces.length
 	while (i--) {
 		var ns = visibleNamespaces[i];
 		// get namespace prefix
@@ -1187,7 +1343,7 @@ function serializeToString(node,buf,isHTML,nodeFilter,visibleNamespaces){
 		var len = attrs.length;
 		var child = node.firstChild;
 		var nodeName = node.tagName;
-		
+
 		isHTML = NAMESPACE.isHTML(node.namespaceURI) || isHTML
 
 		var prefixedNodeName = nodeName
@@ -1246,14 +1402,14 @@ function serializeToString(node,buf,isHTML,nodeFilter,visibleNamespaces){
 			serializeToString(attr,buf,isHTML,nodeFilter,visibleNamespaces);
 		}
 
-		// add namespace for current node		
+		// add namespace for current node
 		if (nodeName === prefixedNodeName && needNamespaceDefine(node, isHTML, visibleNamespaces)) {
 			var prefix = node.prefix||'';
 			var uri = node.namespaceURI;
 			addSerializedAttribute(buf, prefix ? 'xmlns:' + prefix : "xmlns", uri);
 			visibleNamespaces.push({ prefix: prefix, namespace:uri });
 		}
-		
+
 		if(child || isHTML && !/^(?:meta|link|img|br|hr|input)$/i.test(nodeName)){
 			buf.push('>');
 			//if is cdata child node
@@ -1468,7 +1624,7 @@ try{
 				}
 			}
 		})
-		
+
 		function getTextContent(node){
 			switch(node.nodeType){
 			case ELEMENT_NODE:

@@ -1,7 +1,7 @@
-'use strict'
+'use strict';
 
-const { getTestParser } = require('../get-test-parser')
-const { DOMImplementation } = require('../../lib/dom')
+const { getTestParser } = require('../get-test-parser');
+const { DOMImplementation, DOMException } = require('../../lib/dom');
 
 const INPUT = (first = '', second = '', third = '', fourth = '') => `
 <html >
@@ -83,4 +83,68 @@ describe('Document.prototype', () => {
 			expect(doc.firstChild === doctype).toBe(true)
 		})
 	})
+	describe('insertBefore', () => {
+		it('should insert the first element and set `documentElement`', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			expect(doc.childNodes).toHaveLength(0);
+			expect(doc.documentElement).toBeNull();
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(doc.childNodes.item(0)).toBe(root);
+		});
+		it('should prevent inserting a second element', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const second = doc.createElement('second');
+			doc.insertBefore(root);
+			expect(() => doc.insertBefore(second)).toThrow(DOMException);
+			expect(doc.documentElement).toBe(root);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting an element before a doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			const root = doc.createElement('root');
+			expect(() => doc.insertBefore(root, doctype)).toThrow(DOMException);
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(1);
+			expect(root.parentNode).toBeNull();
+		});
+		it('should prevent inserting a second doctype', () => {
+			const impl = new DOMImplementation();
+			const doctype = impl.createDocumentType('DT');
+			const doctype2 = impl.createDocumentType('DT2');
+			const doc = impl.createDocument(null, '', doctype);
+			expect(doc.childNodes).toHaveLength(1);
+			expect(() => doc.insertBefore(doctype2)).toThrow(DOMException);
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting a doctype after an element', () => {
+			const impl = new DOMImplementation();
+			const doc = impl.createDocument(null, '');
+			const root = doc.createElement('root');
+			doc.insertBefore(root);
+			const doctype = impl.createDocumentType('DT');
+			expect(doc.childNodes).toHaveLength(1);
+
+			expect(() => doc.insertBefore(doctype)).toThrow(DOMException);
+
+			expect(doc.childNodes).toHaveLength(1);
+		});
+		it('should prevent inserting before an child which is not a child of parent', () => {
+			const doc = new DOMImplementation().createDocument(null, '');
+			const root = doc.createElement('root');
+			const withoutParent = doc.createElement('second');
+
+			expect(() => doc.insertBefore(root, withoutParent)).toThrow(DOMException);
+
+			expect(doc.documentElement).toBeNull();
+			expect(doc.childNodes).toHaveLength(0);
+			expect(root.parentNode).toBeNull();
+		});
+	});
 })

@@ -38,12 +38,10 @@ describe('XML Node Parse', () => {
 </bookstore>`)
 	})
 
-	it('nested closing tag with whitespace', () => {
-		const actual = new DOMParser()
-			.parseFromString(`<book></book ><title>Harry Potter</title>`, 'text/xml')
-			.toString()
-		expect(actual).toBe(`<book/><title>Harry Potter</title>`)
-	})
+	it('sibling closing tag with whitespace', () => {
+		const actual = new DOMParser().parseFromString(`<xml><book></book ><title>Harry Potter</title></xml>`, 'text/xml').toString();
+		expect(actual).toBe(`<xml><book/><title>Harry Potter</title></xml>`);
+	});
 
 	describe('simple attributes', () => {
 		describe('nothing special', () => {

@@ -316,14 +316,22 @@ Object {
 exports[`xmltest/not-wellformed standalone should match 040.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc>",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
 exports[`xmltest/not-wellformed standalone should match 041.xml with snapshot 1`] = `
 Object {
   "actual": "<doc/>
-<doc/>",
+&lt;doc>",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:2,col:1]",
+  ],
 }
 `;
 
@@ -343,7 +351,12 @@ Illegal data
 
 exports[`xmltest/not-wellformed standalone should match 044.xml with snapshot 1`] = `
 Object {
-  "actual": "<doc/><doc/>",
+  "actual": "<doc/>&lt;doc/>
+",
+  "error": Array [
+    "[xmldom error]	element parse error: Error: Hierarchy request error: Only one element can be added and only after doctype
+@#[line:1,col:7]",
+  ],
 }
 `;