Taking advantage of HTML5 in real-world sites and applications can be a daunting proposition. Though modern browsers are implementing HTML5’s new features at a rapid pace, few of us are lucky enough to write applications supporting only the latest crop of browsers. As a professional web developer, that browser fragmentation forces you to spend significant effort navigating the uncomfortable space between the promise of the future and the realities of the present. The good news is that Internet Explorer 10 and 9 support HTML5. Users are also leaving older versions of Internet Explorer. But the share of older versions is likely to remain just enough for developers to support in the foreseeable future.