Section 28(a) in The Indian Post Office Rules, 1933
(a)The packet shall consist only of articles specially impressed as described above for the use of the blind, and shall not contain any communication either in writing or printed in ordinary type, except the title and table of contents of the book or periodicals, and any key to, or instructions, for the use of the special type, or any enclosure except a label for the return of the packet.
