Patent Cooperation Treaty (PCT)
(1) Subject to the provisions of paragraph (2)(ii), drawings shall be required when they are necessary for the understanding of the invention.
(2) Where, without being necessary for the understanding of the invention, the nature of the invention admits of illustration by drawings:
(i) the applicant may include such drawings in the international application when filed,
(ii) any designated Office may require that the applicant file such drawings with it within the prescribed time limit.