title: Set a image url dynamically into a xsl file
body: <p>I want to create an xsl file (for a xslt transformation to xsl:fo using an xml)
  How can I display a image whose url is stored in the xml file?
  I can use variables</p>
  
  <pre><code>&lt;fo:block-container top="5mm" height="20mm" left="0mm" width="75mm"&gt;
        &lt;fo:block margin-top="10mm" margin-left="50mm"&gt;
          &lt;fo:external-graphic display-align="center" src="url('{$imageUrl}')" content-width="75mm"&gt;&lt;/fo:external-graphic&gt;
        &lt;/fo:block&gt;
      &lt;/fo:block-container&gt;
  </code></pre>
  
  <p>But how can I set the variable's value from a tag from the xml file?</p>
  
  <p>Sample XML from comment:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8" ?&gt;
  &lt;doc&gt; 
    &lt;title&gt;Simple test&lt;/title&gt;
    &lt;image&gt;
      &lt;i&gt;colour_logo.jpg&lt;/i&gt;
    &lt;/image&gt;
    &lt;body&gt;
      &lt;question&gt;
        &lt;p&gt;Is the sky blue?&lt;/p&gt;
      &lt;/question&gt;
      &lt;question&gt; 
        &lt;p&gt;Is the grass blue?&lt;/p&gt; 
      &lt;/question&gt; 
    &lt;/body&gt; 
  &lt;/doc&gt;
  </code></pre>