According to the principles outlined in the accounting standards, any revaluation surplus resulting from the upward revaluation of property, plant, and equipment should not be recognized as an element of earnings but is instead credited to a revaluation reserve in equity. Therefore, the correct accounting treatment for a revaluation surplus is that it is not realized and does not form part of earnings. Instead, it increases the carrying amount of the respective asset and is recognized in shareholders' equity outside of retained earnings, in a separate component called "revaluation reserve."

Hence, the principle that ABC Limited needs to follow is:

Any revaluation surplus is not realized but does form part of earnings.

This means that the increase in the value of the asset due to revaluation is recorded in the balance sheet, enhancing the net assets of the company without directly impacting the profit and loss account.