createContextualFragment() is a method of Range objects that creates a document fragment from an HTML string. It's present in Firefox and WebKit and Opera but is currently non-standard (it's not in the DOM Level 2 Range spec but is in the work-in-progress DOM Parsing and Serialization spec) and IE 9 didn't implement it, which is consistent with Microsoft's general approach to implementing standard functionality in IE 9 that was previously missing in IE. ExtJs must be using this method, although rather foolishly since it is non-standard and the same result can easily be achieved using innerHTML, which is supported everywhere.

UPDATE

You can patch the following into IE 9 since it allows extension of host object prototypes, which previous versions did not. The following is a naive implementation of createContextualFragment() adapted from my Rangy library but is suitable for most uses. See this Rangy issue for details and for a more thorough implementation.

Note that this will not work in IE < 9 because those browsers have no DOM Range implementation.

if (typeof Range.prototype.createContextualFragment == undefined) {

    Range.prototype.createContextualFragment = function(html) {

        var startNode = this.startContainer;

        var doc = startNode.nodeType == 9 ? startNode : startNode.ownerDocument;

        var container = doc.createElement(div);

        container.innerHTML = html;

        var frag = doc.createDocumentFragment(), n;

        while ( (n = container.firstChild) ) {

            frag.appendChild(n);

        }

        return frag;

    };

}