A living will may be in any written form expressing the wishes of a principal regarding the initiation, continuation, withholding or withdrawal of life-sustaining treatment and may include other specific directions, including, but not limited to, designation of a health care agent to make health care decisions for the principal if the principal is determined to be incompetent and to have an end-stage medical condition or is permanently unconscious. An example of a living will appears in the combined form set forth in Subchapter D (relating to combined form).