filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#e7e7e7');
background: -webkit-gradient(linear, left top, left bottom, from(#ffffff), to(#e7e7e7));
These kinds of css properties are removed when filtering input. I'm not sure if this is due to CSSTidy or HTML Purifier. I've tried to look in both of the manuals without finding any clues.