Vendor-specific prefixes

I mentioned earlier that the CSS3 specification is a series of modules that are being slowly rolled out by browser vendors. In some cases this rolling out involves experimental support. That is, while the spec is being written, debated, and hashed out at the W3C, a browser maker might choose to add support for certain properties anyway, testing it in a real-world environment. It’s become a healthy part of the process, where feedback from experimental usage is often used to make adjustments to the spec.

Alternatively, a browser vendor might want to introduce an experimental property that’s not part of any proposed standard, but may become one at a later date.

Often this experimental support for CSS properties is handled by the use of a vendor prefix like so: