Google Website Optimiser Control Javascript

Could someone explain the javascript that makes up Google's Website Optimiser Control script? Specifically: the first two lines, which seem to be empty functions, and why is the third function wrapped parentheses () ?

As far as I can tell this script is basically writing out a new <script> which presumably loads something for A/B testing.

function utmx_section(){}
function utmx(){}
(function() { 
    var k='0634742331',d=document,l=d.location,c=d.cookie;
    function f(n) {
      if(c) { 
        var i=c.indexOf(n+'=');
        if (i>-1) { 
          var j=c.indexOf(';',i);
          return escape(c.substring(i+n.length+1,j<0?c.length:j))
        }
      }
    }
    var x=f('__utmx'),xx=f('__utmxx'),h=l.hash;
    d.write('<sc'+'ript src="'+'http'+(l.protocol=='https:'?'s://ssl':'://www')+'.google-analytics.com'+'/siteopt.js?v=1&utmxkey='+k+'&utmx='+(x?x:'')+'&utmxx='+(xx?xx:'')+'&utmxtime='+new Date().valueOf()+(h?'&utmxhash='+escape(h.substr(1)):'')+'" type="text/javascript" charset="utf-8"></sc'+'ript>')
  }
)()开发者_如何学运维;

I've attempted to step through with the firebug debugger but it doesn't seem to like it. Any insights much appreciated.

Many thanks

inside anonymous function it shortens names of document and cookies inside it at first, function f(n) gets value of cookie under name n. Then Google reads its cookies and with help of d.write it loads its scripts (as I see they are related to Google Analytic). This way it makes On-Demand JavaScript loading... Actually you load these scripts all the time, Google just needs some additional parameters in url, so this is done this way - save parameters in cookie, which next time are used to get script again.

And finally back to the first two magic lines :) After Google loads its script (after executing d.write), there are some functions which uses utmx and utmx_section, as well as definition of these functions, or better to say overriding. I think they are empty at first just because another function can execute it before its real definition, and having empty functions nothing will happen (and no JS error), otherwise script would not work. E.g. after first iteration there is some data, which is used to make real definition of these functions and everything starts to work :)

The first 2 functions are in fact empty, and are probably overridden later on.
The third function is an anonymous self-executing function. The brackets are a convention to make you aware of the fact that it is self executing.
the "f" function looks up the value given to it in the document's cookies and returns it. Then a new script tag is written to document (and requested from server) with these values as part of its URL.