window.addEvent('domready', function() {
    // modified from http://joesong.com/2009/11/external-links-in-new-window-passive-and-with-mootools/ 
    // to avoid using the 'target' attribute, which is not part of xhtml 1.0 strict
    var currentDomain = window.location.host;
    $(document.body).addEvent('click', function(evt) {
	var target = $(evt.target);
	if (target.get('tag') !== 'a') {
	    target = target.getParent();
	}

	if (target && target.get('tag') === 'a' && target.get('href').test('http') && !target.get('href').test(currentDomain)) {
	    window.open(target.get('href'), '_blank');
	    return false;
	}
    });
});

The html attribute 'target="_blank"' for links is no longer valid code as of XHTML Strict 1.0. This code will run using mootools on domready to send all clicks to new windows when going to an external domain.

automatically send external links to new window with mootools

links

JavaScript