15. Before admitting to proof, a will which appears to have been signed by a blind or illiterate testator or by another person by direction of the testator or which for any reason gives rise to doubt as to the testator having had knowledge of the contents of the will at the time of its execution, the registrar shall satisfy himself that the testator had such knowledge. 16. (1) Where there appears in a will any obliteration, interlineation, or other alteration which is not authenticated in the manner prescribed by law or by the re-execution of the will or by the execution of a codicil, the registrar shall require evidence to show whether the alteration was present at the time the will was executed and shall give directions as to the form in which the will is to be proved: Provided that this paragraph shall not apply to any alteration which appears to the registrar to be of no practical importance. (2) If from any mark on the will it appears to the registrar that some other document has been attached to the will or if a will contains any reference to another document in such terms as to suggest that it ought to be incorporated in the will, the registrar may require the document to be produced and may call for such evidence in regard to the attaching or incorporation of the document as he may think fit. (3) Where there is doubt as to the date on which a will was executed, the registrar may require such evidence as he thinks necessary to establish the date. 17. Any appearance of attempted revocation of a will by burning, tearing or otherwise and every other circumstance leading to a presumption of revocation by the testator, shall be accounted for to the registrar's satisfaction. 18. The Registrar may require an affidavit from any person he may think fit for the purpose of satisfying himself as to any of the matters referred to in rules 15, 16 and 17 of this Order, and in any such affidavit sworn by an attesting witness or other person present at the time of the execution of a will, the deponent shall depose to the manner in which the will was executed. 19. If it appears to the registrar that there is prima facie evidence that a will is one to which section 9 of the Wills Act, 1837, or any provision of the equivalent enactment in force in the State, applies, the will may be admitted to proof if the registrar is satisfied that it was made by the testator in accordance with the provisions of that section or enactment, as the case may be. 20. Where evidence as to the law of any country or territory outside the Federal Capital Territory, Abuja, is required on any application for a grant, the Registrar may accept an affidavit from any person whom, having regard to the particulars of his knowledge or experience given in the affidavit, he regards as suitably qualified to give expert evidence of the law in question. 21. Where the deceased died after the commencement of this Order, the person or persons entitled to a grant of probate or administration with the will annexed shall be determined in accordance with following order of priority(a) the executor; (b) any residuary legatee or devisee holding in trust for any other persons; (c) any residuary legatee or devisee for life; (d) the ultimate residuary legatee or devisee, including one entitled on the happening of any contingency or, where the residue is not wholly disposed of by the will, any person entitled to share in the residue not so disposed of or the personal representative of any such person: Provided that(i) unless the registrar otherwise directs, a residuary legatee or devisee whose legacy or devise is vested in interest shall be preferred to one entitled on the happening of a contingency, and