Folded secrets - thread books

Do you know about the folded thread "books" made by the Miao peoples of China? They are quite magical, and a search for images finds many, including these -

using traditional patterns (via)

from the collection of Sarah Foulks (via)

(via)

Here's a version made following the instructions set out by Ruth Smith, who researched these in China and wrote a book about the technique (and is teaching it) -

and another, from another blog -

The Chinese name for these books, I learned here, is zhen xian bao (needle thread pockets).