title: Concat value of all elements
body: <p>I have an xml like the below structure.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt;
  
  &lt;bookstore&gt;
       &lt;book&gt;
            &lt;title lang="eng"&gt;Harry Potter&lt;/title&gt;
            &lt;price&gt;29.99&lt;/price&gt;
       &lt;/book&gt;
  
       &lt;book&gt;
             &lt;title lang="eng"&gt;Learning XML&lt;/title&gt;
             &lt;price&gt;39.95&lt;/price&gt;
       &lt;/book&gt;
  &lt;/bookstore&gt;
  </code></pre>
  
  <p>I have extracted all the <code>title</code> nodes as <code>&lt;xsl:variable name="titles" select="/bookstore/book/title"/&gt;</code>. Now, I would like to  concat these titles enclosing each of them in single quotes and then separating them with commas and store them in a variable so that the output looks like: <code>'Harry Potter','Learning XML'</code>. How can I do that?</p>