I cant understand the following script
As im new to jquery i font this script which is useful for my project to fading the image inside the container

     1   <script type="text/javascript">
     2  	$(document).ready(function(){
     3  	  $("#collage-container img").mouseover(function(){
     4  	  $("#collage-container img").css("z-index",1);
     5  	  $(this).css("z-index",999);
        	  $(this).fadeOut(100,function(){ $(this).fadeIn(1000);  });
        	  });
        	});
        </script>


its hard to understand line 4 and 5. whether line 5 is image??
I cant understand the following script
===

As im new to jquery i font this script which is useful for my project to fading the image inside the container

     1   <script type="text/javascript">
     2  	$(document).ready(function(){
     3  	  $("#collage-container img").mouseover(function(){
     4  	  $("#collage-container img").css("z-index",1);
     5  	  $(this).css("z-index",999);
        	  $(this).fadeOut(100,function(){ $(this).fadeIn(1000);  });
        	  });
        	});
        </script>


its hard to understand line 4 and 5. whether line 5 is image??