Note that the js and css is not minified so it is readable. See tabs-example.js for the tab creation code and tabs-example.css for the css.
var tabs = new YAHOO.ext.TabPanel('tabs1');
tabs.addTab('script', "View Script");
tabs.addTab('markup', "View Markup");
tabs.activate('script');
<div id="tabs1">
<div id="script" class="tab-content">
(Content goes here)
</div>
<div id="markup" class="tab-content">
(Content goes here)
</div>
</div>