Modernizr

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
        <script src="scripts/modernizr-2.6.2-full.js"></script>
        <style>
        .box {
            width: 200px;
            height: 130px;
            padding: 10px;
            border: 1px solid black;
            border-radius: 15px;
        }

            .cssgradients .box {
                background: #ffffff; /* For old browsers */
                background: -moz-linear-gradient(top, #ffffff 1%, #000000 100%); /* FF3.6+ */
                background: -webkit-gradient(linear, left top, left bottom, color-stop(1%,#ffffff), color-stop(100%,#000000)); /* Chrome,Safari4+ */
                background: -webkit-linear-gradient(top, #ffffff 1%,#000000 100%); /* Chrome10+,Safari5.1+ */
                background: -o-linear-gradient(top, #ffffff 1%,#000000 100%); /* Opera 11.10+ */
                background: -ms-linear-gradient(top, #ffffff 1%,#000000 100%); /* IE10+ */
                background: linear-gradient(to bottom, #ffffff 1%,#000000 100%); /* W3C */
            }

            .no-cssgradients .box {
                background: url('gradient.png') 0 0 repeat-x;
            }

            .no-borderradius .box {
                behavior: url('scripts/PIE_uncompressed.htc');
            }
            </style>
</head>
<body>
    <script>
        /// Modernizr

        // polifill == shim == shiv

        //1.adds html5shiv if needed(html5 tags in old browsers IE)

        //2. Destect html 5 suport throught adding classes to the html element
        // class "js" if js is suported or "no-js" , canvas etc.
        // set classses for all supported (not - supported ) features included in installed packet

        //3. Yep/Nope loading of polifills
        // polifill for video tag ... polifill for canvas etc.
        if (Modernizr.canvas) {
            //use canvas
        } else {
            //use canvas alternative
            //or load polifill(modernizr polifills github) or other
        }

        Modernizr.load({
            test: Modernizr.audio,
            //yep: my_audio.js,
            nope: 'http://api.html5media.info/1.1.5/html5media.min.js' // i can load differ css here too
        });
        </script>
        <!--[if lt IE 9]>
        <script src="dist/html5shiv.js"></script>
        <![endif]-->


</body>
</html>