This document discusses using jQuery Mobile to build responsive websites that can automatically render content for different devices using the same HTML markup. It outlines some of the benefits of jQuery Mobile, such as requiring no JavaScript coding to produce pages and supporting many mobile devices. The document also advocates for using Modernizr and media queries to conditionally load stylesheets and scripts depending on the device, allowing a single HTML file rather than separate mobile and desktop sites. This achieves responsive design without needing separate codebases or relying on user agent strings.