code: function (el, fn, obj, overrideContext) {
                  return this.on(el, FOCUSIN, fn, obj, overrideContext);
              }
docs: Attaches a focusin event listener to the specified element for
  the purpose of listening for the focus event on the element's
  descendants.
  @method addFocusListener
  
  @param {String|HTMLElement|Array|NodeList} el An id, an element
  reference, or a collection of ids and/or elements to assign the
  listener to.
  @param {Function} fn        The method the event invokes
  @param {Object}   obj    An arbitrary object that will be
  passed as a parameter to the handler
  @param {Boolean|object}  overrideContext  If true, the obj passed in becomes
  the execution context of the listener. If an
  object, this object becomes the execution
  context.
  @return {Boolean} True if the action was successful or defered,
  false if one or more of the elements
  could not have the listener attached,
  or if the operation throws an exception.
  @static
  @deprecated use YAHOO.util.Event.on and specify "focusin" as the event type.