Actually, the information is found at another excellent Frame + Acrobat site called Microtype.com. The URL for the write-up is
http://www.microtype.com/resources/path_HTmarkers.pdf
and the base web site is, of course,
http://www.microtype.com/
It's not a typo that I did not link these; with the way frames were used the result is a bit unpredictable.