title: XSL error "An attribute whose value must be a QName had the value '300x300'"
body: <p>I get this error when trying to name an attribute with the image dimensions (300x300, 420x420, etc).</p>
  
  <p>When I generate the same elements beginning with a letter, everything goes allright.</p>
  
  <p>Here's what I got:</p>
  
  <pre><code>&lt;xsl:for-each select="additionalImages/image"&gt;
      &lt;xsl:if test="additional_image_dimensions != ''"&gt;
          &lt;xsl:element name="{additional_image_dimensions}"&gt;
              &lt;xsl:value-of select="additionalUrl"/&gt;
          &lt;/xsl:element&gt;
      &lt;/xsl:if&gt;
  &lt;/xsl:for-each&gt;
  </code></pre>
  
  <p>I already tried to concatenate nothing to the string <code>{concat('', additional_image_dimensions)}</code></p>
  
  <p>Here's what I want:</p>
  
  <p><code>&lt;300x300&gt;url&lt;/300x300&gt;</code></p>
  
  <p>Ps.: When I try to put a letter on the beginning, it works:</p>
  
  <pre><code>&lt;x30x30&gt;url&lt;/x30x30&gt;
  &lt;x300x300&gt;url&lt;/x300x300&gt;
  </code></pre>
  
  <p>How can I generate a dynamic element named like <code>&lt;300x300&gt;url&lt;/300x300&gt;</code>?</p>