public static function sanitizePluralExpression($expr)
    {
        // Parse equation
        $expr = explode(';', $expr);
        if (count($expr) >= 2) {
            $expr = $expr[1];
        } else {
            $expr = $expr[0];
        }
        $expr = trim(strtolower($expr));
        // Strip plural prefix
        if (substr($expr, 0, 6) === 'plural') {
            $expr = ltrim(substr($expr, 6));
        }
        // Strip equals
        if (substr($expr, 0, 1) === '=') {
            $expr = ltrim(substr($expr, 1));
        }

        // Cleanup from unwanted chars
        $expr = preg_replace('@[^n0-9:\(\)\?=!<>/%&| ]@', '', $expr);

        return $expr;
    }