VendorPrefixes

Vendor prefixes are a mechanism used in web development to expose nonstandard or experimental CSS features to browsers before they become part of the official CSS specification. They consist of a hyphenated prefix added to a property name or value, such as -webkit-, -moz-, -ms-, -o-, or -khtml-. By applying these prefixes, browser vendors can implement new capabilities while avoiding conflicts with future standard definitions and encourage early feedback from developers.

Prefixes are most commonly employed during feature testing and early adoption. When a feature is still in flux, a browser may only recognize the prefixed version of a property. Developers typically provide both prefixed and unprefixed declarations, with the standard form placed after the prefixed ones so that modern browsers use the unprefixed property when available.

Examples of historically prefixed properties include border-radius, transform, transition, animation, and linear-gradient values. While some of these have since become standard and unprefixed across major browsers, others remain for legacy support. The use of prefixes has diminished as CSS specifications stabilize, but they remain present for certain features or older browser versions.

Best practice today involves targeting supported browsers with caniuse data and using tools such as Autoprefixer to automatically generate the necessary prefixed rules. Developers are advised to rely on standard CSS where possible and to test across browsers, using feature queries (@supports) to detect capabilities rather than relying solely on prefixes.