18.-(1) Where a will contains a reference to any document of such a nature as to raise a question whether it ought or ought not to form a constituent part of the will, the probate registrar shall require the production of the document, with a view to ascertaining whether or not it is entitled to probate ; and if it is not produced, a satisfactory account of its non-production shall be proved. A document cannot form part of a will unless it was in existence at the time when the will was executed.
(2) If there are vestiges of sealing wax or wafers, or other marks on the will, leading to the inference that some document has been at some time annexed or attached thereto, a satisfactory account of them shall be proved, and the production of the document shall be required, and if it is not produced, a satisfactory account of its non-production shall be proved.