title: Nested single/double quotes in Javascript/jQuery
body: <p>I had thought that single/double quotes were interchangeable in Javascript. So in a jQuery function, could anyone explain why:</p>
  
  <pre><code>$('input:radio[name='+foo+'][value='+bar+']').attr('checked', true);
  </code></pre>
  
  <p>works, but </p>
  
  <pre><code>$('input:radio[name="+foo+"][value="+bar+"]').attr('checked', true);
  </code></pre>
  
  <p>doesn't? (If <code>foo</code> and <code>bar</code> are both strings.) </p>
  
  <p>Does nesting double in single/single in double quotes not work?</p>