protected function checkElementNode(DOMElement $element, Tag $tag)
	{
		$xpath = new DOMXPath($element->ownerDocument);

		// If current node is not an <xsl:attribute/> element, we exclude descendants
		// with an <xsl:attribute/> ancestor so that content such as:
		//   <script><xsl:attribute name="id"><xsl:value-of/></xsl:attribute></script>
		// would not trigger a false-positive due to the presence of an <xsl:value-of/>
		// element in a <script>
		$predicate = ($element->localName === 'attribute') ? '' : '[not(ancestor::xsl:attribute)]';

		// Test the select expression of <xsl:value-of/> nodes
		$query = './/xsl:value-of' . $predicate;
		foreach ($xpath->query($query, $element) as $valueOf)
		{
			$this->checkSelectNode($valueOf->getAttributeNode('select'), $tag);
		}

		// Reject all <xsl:apply-templates/> nodes
		$query = './/xsl:apply-templates' . $predicate;
		foreach ($xpath->query($query, $element) as $applyTemplates)
		{
			throw new UnsafeTemplateException('Cannot allow unfiltered data in this context', $applyTemplates);
		}
	}