protected function checkAttribute(DOMNode $node, Tag $tag, $attrName)
	{
		// Test whether the attribute exists
		if (!isset($tag->attributes[$attrName]))
		{
			if ($this->ignoreUnknownAttributes)
			{
				return;
			}

			throw new UnsafeTemplateException("Cannot assess the safety of unknown attribute '" . $attrName . "'", $node);
		}

		// Test whether the attribute is safe to be used in this content type
		if (!$this->tagFiltersAttributes($tag) || !$this->isSafe($tag->attributes[$attrName]))
		{
			throw new UnsafeTemplateException("Attribute '" . $attrName . "' is not properly sanitized to be used in this context", $node);
		}
	}