joint.all.js
function() {

        var el;

        if (!this.el) {

            var attrs = _.extend({ id: this.id }, _.result(this, 'attributes'));
            if (this.className) attrs['class'] = _.result(this, 'className');
            el = V(_.result(this, 'tagName'), attrs).node;

        } else {

            el = _.result(this, 'el')
        }

        this.setElement(el, false);
    }
function() {

        var el;

        if (!this.el) {

            var attrs = _.extend({ id: this.id }, _.result(this, 'attributes'));
            if (this.className) attrs['class'] = _.result(this, 'className');
            el = V(_.result(this, 'tagName'), attrs).node;

        } else {

            el = _.result(this, 'el')
        }

        this.setElement(el, false);
    }
Override the Backbone `_ensureElement()` method in order to create a `<g>` node that wraps all the nodes of the Cell view.