Michigan Compiled Laws, Chapter 700. Estates and Protected Individuals Code § 700.5202

Sec. 5202. (1) The parent of an unmarried minor may appoint a guardian for the minor by will or by another writing signed by the parent and attested by at least 2 witnesses.

(2) Subject to the right of the minor under section 5203,  1 if both parents are dead or have been adjudged to be legally incapacitated or the surviving parent has no parental rights or has been adjudged to be legally incapacitated, a parental appointment becomes effective when the guardian's acceptance is filed in the court in which the will containing the nomination is probated or, if the nomination is contained in a nontestamentary nominating instrument or the testator who made the nomination is not deceased, when the guardian's acceptance is filed in the court at the place where the minor resides or is present. If both parents are dead, an effective appointment by the parent who died later has priority.

(3) A parental appointment effected by filing the guardian's acceptance under a will probated in the state of the testator's domicile is effective in this state.

(4) Upon acceptance of appointment, the guardian shall give written notice of acceptance to the minor and to the person having the minor's care or the minor's nearest adult relative.