https://www.iteye.com/blog/936606539-2427101
Private Property Description browser
Why should private prefix it? Because the development of HTML and CSS standards organization W3C action is very slow. Typically, members of a new property w3c organizations, such as fillet border-radius, we all feel good, but not w3c developing standards for this property, but to go very complicated procedure, after a lot of scrutiny. And the browser are unwilling to wait that long, they feel that a property has been mature enough, it will add support in the browser. But after avoiding future be published w3c standards when changes will join a private prefix, such as -webkit-border-radius, in this way to support the new property in advance, wait until later published w3c standard, the standard wording border-radius of the establishment , let the new version of the browser border-radius support such an approach.