Javascript: IE blink

function doBlink() {
  var blink = document.all.tags("BLINK");
  for (var i=0; i < blink.length; i++) {
    blink[i].style.visibility = (blink[i].style.visibility =="visible") ? "hidden":"visible";
  }
}
if (document.all) setInterval("doBlink()",500);