HTML5 and CSS3 feature-detection with Modernizr library
Ten years ago, only the most cutting-edge web designers used CSS for layouts and styling. Browser support for CSS layouts was slim and buggy, so these people advocated for web standards adherence, while creating hacks that made CSS layouts work in all browsers. One hack that became widely used was browser sniffing: Detecting which browser and version the user had by looking at the navigator.userAgent property in JavaScript. Browser sniffing allowed for quick and easy code forking, allowing developers to target different browsers with different instructions.
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