Questi codici non vengono validati come css3, eppure funzionano

codice:
background:-webkit-gradient(linear, left top, left bottom, from(#ffffff), to(#e5e5e5)); /*Safari e Chrome*/
background:-moz-linear-gradient(top, #ffffff, #d4d4d4); /* per Firefox */ 
background:-o-linear-gradient(top, #ffffff, #d4d4d4); /* per Opera */
filter:progid: DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#d4d4d4'); /* per IE6-7 */  
-ms-filter:"progid: DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#d4d4d4')"; /* IE8 */