public function lessThanOrEqual( $other )
	{
		return $this->namespaceURI == null && $other->namespaceURI ||
		$this->namespaceURI && $other->namespaceURI && $this->namespaceURI < $other->namespaceURI ||
		$this->namespaceURI == $other->namespaceURI && $this->localName <= $other->localName;
	}