When I read the An Introduction to Programming in Emacs Lisp, I found a mistake in let Prevents Confusion, which is node in section 6 of Chapter 3.
At the end of the third paragraph, it said, "in Emacs Lisp, scoping is dynamic, not lexical"
But in version 24.1, Lexical binding was introduced to Emacs.
I think that needs to be made clear.