A durable power of attorney is a power of attorney by which a principal designates another person as attorney-in-fact in writing and the power of attorney contains any of the following statements:

1. (a) “This power of attorney shall not be affected by subsequent incapacity of the principal.”
2. (b) “This power of attorney shall become effective upon the incapacity of the principal.”
3. (c) Similar words showing the intent of the principal that the authority conferred shall be exercisable notwithstanding the principal’s subsequent incapacity.