[a3n]

> My pol­icy for Prac­ti­cal Ty­pog­ra­phy was sim­ple: read­ing the book would re­quire no pre­pay­ment. ... Call it an honor sys­tem. I’ve never used the term free to de­scribe the book, be­cause I don’t see it that way.

The book is not free, it's just that the seller leaves it up to you when to pay for it. He's experimenting with a payment protocol different than the one that most of us have used for thousands of years.