Watermark Mootools Help

I'm a mootools beginner. I know a lot of html and css but javascript is not for me (at least now that I'm starting to learn it)... I saw this post: http://davidwalsh.name/mootools-

Solution 1:

window.addEvent('domready', function() {
   $('gototop').setStyle('display','none');
   ((window.getScrollSize().y + 300 )> window.getSize().y) ? $('gototop').fade(1) : $('gototop').fade(0)  
});