• Modernizer is an open source JavaScript library that detects which HTML5 and CSS3 features your visitor’s browser supports.
• There are several new features which are being introduced through HTML5 and CSS3 but same time many browsers do not support these news features.
• Modernizer provides an easy way to detect any new feature so that you can take corresponding action. For example, if a browser does not support video feature then you would like to display a simple page.
• syntax:

< script src="modernizer.mi.js" type="text/javascript">< /script>

• When we specify the modernizer script in web page , it detects whether current browser supports such as font-face, border-radius, border image etc. in CSS3.
• It also detects HTML5 features such as audio, video, localStorage and the drag ad drop features.
• Modernizer runs automatically by creating a global object, which contain a set of Boolean properties to detect any feature.
• In detecting feature support, it allows developers to test for some of the new technologies and then provide fallbacks for browsers that do not support them. This is called feature detection.