处理IE6下默认不缓存背景图片

if ($.browser.msie && parseInt($.browser.version, 10) < 7) {
        try {
            document.execCommand("BackgroundImageCache", false, true)
        } catch (e) {
        }
    }

<!--[if IE 6]>
<script type="text/javascript">
//<![CDATA[
try {
  document.execCommand("BackgroundImageCache", false, true);
} catch(e) {}
//]]>
</script>
<![endif]-->

html {
  filter:expression(document.execCommand("BackgroundImageCache",false,true));
}