使IE8以下的IE浏览器也支持图片的data协议

参见[url]http://www.phpied.com/mhtml-when-you-need-data-uris-in-ie7-and-under/[/url]
测试页面：[url]http://phpied.com/files/mhtml/mhtml.html[/url]

原理是使用MHTML（Multipurpose Internet Mail Extensions HyperText Markup Language） hack

/*Content-Type: multipart/related; boundary="_ANY_STRING_WILL_DO_AS_A_SEPARATOR"--_ANY_STRING_WILL_DO_AS_A_SEPARATORContent-Location:locolocoContent-Transfer-Encoding:base64iVBORw0KGgoAAAANSUhEUgAAAAQAAAADCAIAAAA7ljmRAAAAGElEQVQIW2P4DwcMDAxAfBvMAhEQMYgcACEHG8ELxtbPAAAAAElFTkSuQmCC--_ANY_STRING_WILL_DO_AS_A_SEPARATORContent-Location:pollolocoContent-Transfer-Encoding:base64iVBORw0KGgoAAAANSUhEUgAAABkAAAAUBAMAAACKWYuOAAAAMFBMVEX///92dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnYvD4PNAAAAD3RSTlMAACTkfhvbh3iEewTtxBIFliR3AAAAUklEQVQY02NgIBMwijgKCgrAef5fkHnz/y9E4kn+/4XEE6z/34jEE///A4knev7zAwQv7L8RQk40/7MiggeUQpjJff+zIpINykbIbhFSROIRDQAWUhW2oXLWAQAAAABJRU5ErkJggg==*/#test1 {  background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAADCAIAAAA7ljmRAAAAGElEQVQIW2P4DwcMDAxAfBvMAhEQMYgcACEHG8ELxtbPAAAAAElFTkSuQmCC"); /* normal */  *background-image: url(mhtml:http://phpied.com/files/mhtml/mhtml.css!locoloco); /* IE < 8 */}#test2 {  background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABkAAAAUBAMAAACKWYuOAAAAMFBMVEX///92dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnZ2dnYvD4PNAAAAD3RSTlMAACTkfhvbh3iEewTtxBIFliR3AAAAUklEQVQY02NgIBMwijgKCgrAef5fkHnz/y9E4kn+/4XEE6z/34jEE///A4knev7zAwQv7L8RQk40/7MiggeUQpjJff+zIpINykbIbhFSROIRDQAWUhW2oXLWAQAAAABJRU5ErkJggg=="); /* normal */  *background-image: url(mhtml:http://phpied.com/files/mhtml/mhtml.css!polloloco); /* IE < 8 */}div {  width: 100px;  height: 100px;  font: bold 24px Arial;}

好处是啥？减少HTTP请求（这些图片不会单独再发请求了）。