protected function checkVariable(DOMNode $node, $tag, $qname)
	{
		// Test whether this variable comes from a previous xsl:param or xsl:variable element
		$this->checkVariableDeclaration($node, $tag, 'xsl:param[@name="' . $qname . '"]');
		$this->checkVariableDeclaration($node, $tag, 'xsl:variable[@name="' . $qname . '"]');
	}