joint.all.js
function() {

        var markup = this.model.markup || this.model.get('markup');
        
        if (markup) {

            var nodes = V(markup);
            V(this.el).append(nodes);
            
        } else {

            throw new Error('properties.markup is missing while the default render() implementation is used.');
        }

        this.update();

        this.resize();
        this.rotate();
        this.translate();        

        return this;
    }
function() {

        var markup = this.model.markup || this.model.get('markup');
        
        if (markup) {

            var nodes = V(markup);
            V(this.el).append(nodes);
            
        } else {

            throw new Error('properties.markup is missing while the default render() implementation is used.');
        }

        this.update();

        this.resize();
        this.rotate();
        this.translate();        

        return this;
    }
`prototype.markup` is rendered by default. Set the `markup` attribute on the model if the default markup is not desirable.