<script type="text/javascript">
Event.observe(window, 'load', function() {
    $$('a[rel="external"]').each(function(link){
        if(link.readAttribute('href') != '' && link.readAttribute('href') != '#'){
            link.writeAttribute('target','_blank');
        }
    });
});
</script>

http://blog.ninedays.org/2008/04/07/change-rel-external-to-target-blank-using-prototype/

There's been a popular trend to use JavaScript to add target="_blank" to anchors with rel="external". So in the name of making everything in my site Prototype based I worked out a script to do just that.

Change Rel External to Target Blank using Prototype

html, links

JavaScript