"There are dark corners in the Bourne shell, and people use all of them."
https://books.google.com/books?id=KJQRAwAAQBAJ&pg=PA36&lpg=P...
https://books.google.com/books?id=KJQRAwAAQBAJ&pg=PA36&lpg=P...
https://www.linuxjournal.com/article/2800
The latest revision of that text seems to be available here: