A convenient way to set nested attributes.
function(attrs, value, opt) {

        var currentAttrs = this.get('attrs');
        var delim = '/';
        
        if (_.isString(attrs)) {
            // Get/set an attribute by a special path syntax that delimits
            // nested objects by the colon character.

            if (value) {

                var attr = {};
                joint.util.setByPath(attr, attrs, value, delim);
                return this.set('attrs', _.merge({}, currentAttrs, attr), opt);
                
            } else {
                
                return joint.util.getByPath(currentAttrs, attrs, delim);
            }
        }
        
        return this.set('attrs', _.merge({}, currentAttrs, attrs), value);
    }