A nursing student is reviewing the concept of advance directives in preparation for their upcoming NCLEX-RN examination. They come across a particular scenario where a patient, after a recent diagnosis of terminal cancer, expresses their wish not to undergo any life-sustaining treatments. The student recalls that advance directives can take various forms. One specific type of advance directive in which a patient can designate a health care proxy to make decisions on their behalf when they are unable to do so is known as a '_____'.