title: jQuery: Re-write $('foo+bar') selector to use $foo variable
body: <p>Right now I'm using the jQuery selector <code>$('foo+bar')</code>.  Since I already have <code>$('foo')</code> stored in a variable <code>$foo</code>, I'd like to re-write my selector to use the <code>$foo</code> variable.  How do you do that?</p>
  
  <p>I'm looking for something simple.  I'd rather burn a few CPU cycles by using code that's easy to understand rather than write something complicated.</p>