(1) Subject to section 1202, and except as provided in subsection (2) and in sections 2503, 2506, and 2513, a will is valid only if it is all of the following:

    (a) In writing.

    (b) Signed by the testator or in the testator's name by some other individual in the testator's conscious presence and by the testator's direction.

    (c) Signed by at least 2 individuals, each of whom signed within a reasonable time after he or she witnessed either the signing of the will as described in subdivision (b) or the testator's acknowledgment of that signature or acknowledgment of the will.

    (2) A will that does not comply with subsection (1) is valid as a holographic will, whether or not witnessed, if it is dated, and if the testator's signature and the document's material portions are in the testator's handwriting.

    (3) Intent that the document constitutes a testator's will can be established by extrinsic evidence, including, for a holographic will, portions of the document that are not in the testator's handwriting.