One Web

Websites should be built so that people can access them quickly and easily, regardless of the device they’re using (which will mean different input methods and capabilities), the type of connection they are on, or any disabilities they have. That means building things with Progressive Enhancement, and embracing the fluid nature of the web.

Robust websites should be built with a separation of concerns: HTML for structured content; CSS for presentation; JavaScript for behaviour. The JavaScript should add any extra markup it needs.