Implementation as per HTML parsing spec, trusting in the browser's implementation of innerHTML. See discussion and base code for this implementation at issue 67. Spec: http://html5.org/specs/dom-parsing.html#extensions-to-the-range-interface Thanks to Aleks Williams.
function(fragmentStr) {
            // "Let node the context object's start's node."
            var node = this.startContainer;
            var doc = dom.getDocument(node);

            // "If the context object's start's node is null, raise an INVALID_STATE_ERR
            // exception and abort these steps."
            if (!node) {
                throw new DOMException("INVALID_STATE_ERR");
            }

            // "Let element be as follows, depending on node's interface:"
            // Document, Document Fragment: null
            var el = null;

            // "Element: node"
            if (node.nodeType == 1) {
                el = node;

            // "Text, Comment: node's parentElement"
            } else if (dom.isCharacterDataNode(node)) {
                el = dom.parentElement(node);
            }

            // "If either element is null or element's ownerDocument is an HTML document
            // and element's local name is "html" and element's namespace is the HTML
            // namespace"
            if (el === null || (
                el.nodeName == "HTML"
                && dom.isHtmlNamespace(dom.getDocument(el).documentElement)
                && dom.isHtmlNamespace(el)
            )) {

            // "let element be a new Element with "body" as its local name and the HTML
            // namespace as its namespace.""
                el = doc.createElement("body");
            } else {
                el = el.cloneNode(false);
            }

            // "If the node's document is an HTML document: Invoke the HTML fragment parsing algorithm."
            // "If the node's document is an XML document: Invoke the XML fragment parsing algorithm."
            // "In either case, the algorithm must be invoked with fragment as the input
            // and element as the context element."
            el.innerHTML = fragmentStr;

            // "If this raises an exception, then abort these steps. Otherwise, let new
            // children be the nodes returned."

            // "Let fragment be a new DocumentFragment."
            // "Append all new children to fragment."
            // "Return fragment."
            return dom.fragmentFromNodeChildren(el);
        }