So we've looked at responsive web design. It seems extremely powerful but a lot of it takes place on the client side. Wouldn't it be very advantageous to have some of that work take place server-side so that it will be more efficient for your users? Enter RESS.

It is an answer to the problems that plague standardized RWD. With a large number of media queries, coupled with scaling images on the client, your website can become quite large. The larger the website, the longer it takes to load. By using a server-side language, such as PHP in this book, we can still execute some RWD but have our server handle a greater amount of the load, thereby speeding up page loads. Of course we are not going to just use PHP by itself, we are going to also use what we just learned with Modernizr and WURFL to make our applications truly responsive.

RESS is a fairly new technique, with the phrase first coined by Luke Wroblewski in 2011. By using it, we can actually do more RWD by dynamically...