In XHTML 1.1, there is no arrtibute target="" anymore but sometimes you want to open a link in a new window. Just as CSS3 is interpreted by all browsers, you can easily do this like this:
.new {
target-new: new ! important
}
You can cann this CSS-class like this :
<a href="http://www.w3.org" class="new">w3.org</a>
Because the releasedate of CSS3 is almost unknown you can use javascript to open a link in a new window and stay XHTML valid.
<a href="http://www.w3.org" onclick="void(window.open(this.href, '', '')); return false;">w3.org</a>
Furter information about CSS3 you'll find
here