<span><!-- Grab Google CDN's jQuery. fall back to local if necessary -->
<script src="<a class="linkclass" href="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js">http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js</a>"></script>
<script>!window.jQuery && document.write('<script src="js/jquery-1.4.2.min.js"></script>')</script>
</span>

<span><!-- Grab Google CDN's jQuery. fall back to local if necessary -->
2
<script src="<a class="linkclass" href="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js">http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js</a>"></script>
3
<script>!window.jQuery && document.write('<script src="js/jquery-1.4.2.min.js"></script>')</script>
4
</span>

http://www.1stwebdesigner.com/development/snippets-html5-boilerplate/

jQuery loading fallback

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