code: function() {
  
          var element = this.model;
          var markup = element.get('markup') || element.markup;
          if (!markup) throw new Error('dia.ElementView: markup required');
          if (Array.isArray(markup)) return this.renderJSONMarkup(markup);
          if (typeof markup === 'string') return this.renderStringMarkup(markup);
          throw new Error('dia.ElementView: invalid markup');
      }
docs: `prototype.markup` is rendered by default. Set the `markup` attribute on the model if the default markup is not desirable.