Need help for javascript of FCKeditor

I am use FCKeditor, How can i get the instance value of the textarea??

below is my script:
head-->
window.onfiltered= function()
{
var oFCKeditor1 = new FCKeditor( 'detail' ) ;
oFCKeditor1.ReplaceTextarea() ;
}
</script>

function preview(){
var predetail = oFCKeditor1.Value; //what should i put here to output the value of the
//textarea vale
window.open( '../index.php?=' + predetail,'','');
}
</script>
.....................................
body-->
<form>
<textarea name="detail" cols="50" rows="8"></textarea><br>
<a href="http://mail.yahoo.com/config/login?/_javascript: preview();">Preview</a>
</form>