Vendor prefix

A CSS hack is a coding technique used to hide or show CSS markup depending on the browser, version number, or capabilities. Browsers have different interpretations of CSS behavior and different levels of support for the W3C standards. CSS hacks are sometimes used to achieve consistent layout appearance in multiple browsers that do not have compatible rendering. Most of these hacks do not work in modern versions of the browsers, and other techniques, such as feature support detection, have become more prevalent.

Due to quirks in the interpretation of CSS by various browsers, most CSS hacks involve writing invalid CSS rules that are interpreted only by specific browsers, or relying on bugs in specific browsers. An example of this is prefixing rules with an underscore (as in _width) to target Internet Explorer 6—other browsers will ignore the line, allowing it to be used to write code specific to one browser.

Prior to version 10, Internet Explorer supported a special comment syntax that would allow blocks of HTML to be read only by specific versions of the browser. These comments are mostly used to provide specific CSS and JavaScript workarounds to older versions of the browser. No other browsers interpreted these comments or offered similar functionality.

The following are examples of the different syntax for these comments.

Hiding code using hacks often leads to pages being incorrectly displayed when browsers are updated. These hacks can lead to unexpected behavior in newer browsers that may interpret them differently than their predecessors. Since Internet Explorer 6 and 7 have fallen out of use, CSS hacks have declined as well. Modern methods of feature targeting are less fragile and error-prone.

Each of the most popular browser rendering engines has its own vendor-specific prefix for experimental properties. However, due to the proliferation of these properties in live code, the browser vendors have begun to move away from this in favor of user-controlled feature flags.

The following is a list of prefixes from various layout engines:

Vendor prefixes were designed for features that were under development, meaning that the syntax may not even be final. Also, adding a rule for each browser's implementation of a function does not scale well when you want to support many browsers. Consequently, the major browser vendors are moving away from vendor prefixes in favor of other methods such as @supports feature queries.

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