When you need to add multiple values, there is little sense in doing separate operations (and also creating intermediate objects) like: ``` javascript const a = ImmutableMap([['x', 1], ['y', 2]]); const b = a.set('z', 3).set('t', 4); ``` It would be nice to have `.extend` method that would allow to do things like: ``` javascript const a = ImmutableMap([['x', 1], ['y', 2]]); const b = a.extend({z: 3, t: 4}); // or a.extend(#{z: 3, t: 4}); ```