on page 135 there is the following excerpt from tooltips.js:

Code:
  showTipListener: function(event)
  {
    Tooltips.showTip(this);
    Core.preventDefault(event);
  },
  
  hideTipListener: function(event)
  {
    Tooltips.hideTip(this);
  }
1. why is showTip using "this" but preventDefault using "event" ?

2. why is hideTip using "this" when "event" is the parameter?

i know it's right under my nose but i'm not quite getting it

many thanks