For the MDN documentation website we have written this jsonToDOM function and I was wondering how you all would improve it. It takes a json structure and creates DOM elements out of it and appends it to the document. It is written in such a way that the user has to pass the window/document as they might run this code from a scope which has no access to window object (Browser addons for example)

This is an example of how I use it: https://gist.github.com/Noitidart/9523055#file-_ff-addon-snippet-createmenuwithsubmenuandattachtowidget-js-L6

jsonToDOM.namespaces = {
    html: 'http://www.w3.org/1999/xhtml',
    xul: 'http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul'
};
jsonToDOM.defaultNamespace = jsonToDOM.namespaces.html;
function jsonToDOM(xml, doc, nodes) {
    function namespace(name) {
        var m = /^(?:(.*):)?(.*)$/.exec(name);        
        return [jsonToDOM.namespaces[m[1]], m[2]];
    }

    function tag(name, attr) {
        if (Array.isArray(name)) {
            var frag = doc.createDocumentFragment();
            Array.forEach(arguments, function (arg) {
                if (!Array.isArray(arg[0]))
                    frag.appendChild(tag.apply(null, arg));
                else
                    arg.forEach(function (arg) {
                        frag.appendChild(tag.apply(null, arg));
                    });
            });
            return frag;
        }

        var args = Array.slice(arguments, 2);
        var vals = namespace(name);
        var elem = doc.createElementNS(vals[0] || jsonToDOM.defaultNamespace, vals[1]);

        for (var key in attr) {
            var val = attr[key];
            if (nodes && key == 'key')
                nodes[val] = elem;

            vals = namespace(key);
            if (typeof val == 'function')
                elem.addEventListener(key.replace(/^on/, ''), val, false);
            else
                elem.setAttributeNS(vals[0] || '', vals[1], val);
        }
        args.forEach(function(e) {
            try {
                elem.appendChild(
                                    Object.prototype.toString.call(e) == '[object Array]'
                                    ?
                                        tag.apply(null, e)
                                    :
                                        e instanceof doc.defaultView.Node
                                        ?
                                            e
                                        :
                                            doc.createTextNode(e)
                                );
            } catch (ex) {
                elem.appendChild(doc.createTextNode(ex));
            }
        });
        return elem;
    }
    return tag.apply(null, xml);
}