protected function evaluateOperator($value, $operator, $operand)
    {
        switch ($operator) {
            case '=':
                return $value === $operand;
            case '!=':
                return $value !== $operand;
            case '<':
                return $value < $operand;
            case '<=':
                return $value <= $operand;
            case '>':
                return $value > $operand;
            case '>=':
                return $value >= $operand;
            case '$=':
                if (is_array($value)) {
                    if ($this->evaluateOperator(end($value), '=', $operand)) {
                        return true;
                    }
                    return false;
                } else {
                    return strrpos($value, (string)$operand) === strlen($value) - strlen($operand);
                }
            case '^=':
                if (is_array($value)) {
                    if ($this->evaluateOperator(reset($value), '=', $operand)) {
                        return true;
                    }
                    return false;
                } else {
                    return strpos($value, (string)$operand) === 0;
                }
            case '*=':
                if (is_array($value)) {
                    foreach ($value as $item) {
                        if ($this->evaluateOperator($item, '=', $operand)) {
                            return true;
                        }
                    }
                    return false;
                } else {
                    return strpos($value, (string)$operand) !== false;
                }
            case 'instanceof':
                if ($this->operandIsSimpleType($operand)) {
                    return $this->handleSimpleTypeOperand($operand, $value);
                } else {
                    return ($value instanceof $operand);
                }
            case '!instanceof':
                if ($this->operandIsSimpleType($operand)) {
                    return !$this->handleSimpleTypeOperand($operand, $value);
                } else {
                    return !($value instanceof $operand);
                }
            default:
                return ($value !== null);
        }
    }