mouseenter

<ul id="test">
  <li>
    <ul class="enter-sensitive">
      <li>item 1-1</li>
      <li>item 1-2</li>
    </ul>
  </li>
  <li>
    <ul class="enter-sensitive">
      <li>item 2-1</li>
      <li>item 2-2</li>
    </ul>
  </li>
</ul>

<script>
  var delegationSelector = ".enter-sensitive";

  document.getElementById("test").addEventListener(
    "mouseover",
    function (event) {
      var target = event.target,
        related = event.relatedTarget,
        match;

      // search for a parent node matching the delegation selector
      while (
        target &&
        target != document &&
        !(match = matches(target, delegationSelector))
      ) {
        target = target.parentNode;
      }

      // exit if no matching node has been found
      if (!match) {
        return;
      }

      // loop through the parent of the related target to make sure that it's not a child of the target
      while (related && related != target && related != document) {
        related = related.parentNode;
      }

      // exit if this is the case
      if (related == target) {
        return;
      }

      // the "delegated mouseenter" handler can now be executed
      // change the color of the text
      target.style.color = "orange";
      // reset the color after a small amount of time
      setTimeout(function () {
        target.style.color = "";
      }, 500);
    },
    false,
  );

  // function used to check if a DOM element matches a given selector
  // the following code can be replaced by this IE8 compatible function: https://gist.github.com/2851541
  function matches(elem, selector) {
    // the matchesSelector is prefixed in most (if not all) browsers
    return elem.matchesSelector(selector);
  }
</script>