protected function getTextContent($expr)
	{
		$expr = trim($expr);

		if (preg_match('(^(?:\'[^\']*\'|"[^"]*")$)', $expr))
		{
			return substr($expr, 1, -1);
		}

		if (preg_match('(^0*([0-9]+(?:\\.[0-9]+)?)$)', $expr, $m))
		{
			// NOTE: we specifically ignore leading zeros
			return $m[1];
		}

		return false;
	}