L-attributed definitions include all syntax-directed definitions based on LL(1) grammars
L-attributed definitions are definition whose attributes can be evaluated in depth-first order (as they say in the first sentence).
The statement &quot;L-attributed definitions include all syntax-directed definitions based on LL(1) grammars&quot; is perhaps a bit subtle. It's not saying that the two sets of definitions are the same; rather, that syntax-directed definitions &quot;based on LL(1) grammars&quot; are a subset of L-attributed definitions.
That's true because the predictive parser based on the LL(1) grammar visits the parse tree in strictly depth-first order. This was already noted in Designing a Predictive Parser in Section 2.4 of the text book, which goes on to build a recursive-descent parser illustrating how this works.