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Last week one of the guy's at our office did a talk on using Google's Website Optimizer for AB multivariate testing. In the talk, he says that when you set it up you just add some special code to the page around the HTML you want to vary [ see #3 under multivariate test here ]

<script>utmx_section("Headline")</script>
Welcome!
</noscript>

What's going on with that unbalanced tag at the end? What magic is Google doing?

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should be tagged google-website-optimizer, not google-webmaster-tools –  Yahel Sep 3 '10 at 18:38
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1 Answer 1

up vote 6 down vote accepted

The utmx_section("Headline") command will execute as the document is parsed. If it emits a <noscript> tag using document.write() the browser will ignore that particular section, until it meets the </noscript> tag.

Here is the same trick, but with a h1:

<html>
  <head><title>Spike</title></head>
  <body>
    <script>document.write('<h1>');</script>
      Header
    </h1>
    <p>That's how...</p>
</html>

this will give a body looking like

    <h1>Header</h1>
    <p>That's how...</p>
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Why they do it this way is beyond me though - if you want xhtml or have an XML oriented rendering engine the unbalanced </noscript> tag is a huge issue. –  mawtex Sep 3 '10 at 20:07
    
Ah, that's a better explanation than what Google has(google.com/support/websiteoptimizer/bin/…). +1 –  Lèse majesté Sep 3 '10 at 20:07
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