I suspect it's from the AISC Textbook of Structural Shop Drafting, Volume 3. I have a first edition here in my office. Although I can't find the exact verbiage of the page you linked to, the subject is similar to chapter 26 in my version. Of course, mine is dated 1964 (it's a 4th printing), so subsequent editions may have what you're looking for. My Volume 3 starts at chapter 22, so I'd stay with that Volume.
If you "heard" it on the internet, it's guilty until proven innocent. - DCS