(a) An adult who is not incapacitated may execute a declaration for mental health treatment. The preferences or instructions may include consent to or refusal of mental health treatment.
(b) A declaration for mental health treatment is effective on execution as provided by this chapter. Except as provided by Subsection (c), a declaration for mental health treatment expires on the third anniversary of the date of its execution or when revoked by the principal, whichever is earlier.

(c) If the declaration for mental health treatment is in effect and the principal is incapacitated on the third anniversary of the date of its execution, the declaration remains in effect until the principal is no longer incapacitated.