1. Constraint Validation API

   API for better control over form field validation. Includes support for `checkValidity()`, `setCustomValidity()`, `reportValidity()` and validation states.

2. DOM manipulation convenience methods

   jQuery-like methods on DOM nodes to insert nodes around or within a node, or to replace one node with another. These methods accept any number of DOM nodes or HTML strings as arguments. Includes: `ChildNode.before`, `ChildNode.after`, `ChildNode.replaceWith`, `ParentNode.prepend`, and `ParentNode.append`.

3. ECMAScript 2015 (ES6)

   Support for the ECMAScript 2015 specification. Features include Promises, Modules, Classes, Template Literals, Arrow Functions, Let and Const, Default Parameters, Generators, Destructuring Assignment, Rest & Spread, Map/Set & WeakMap/WeakSet and many more.

4. String.prototype.includes

   The includes() method determines whether one string may be found within another string, returning true or false as appropriate.