Where the text says:

   ... you need to define two apply methods in the CanBuildFrom trait

it should probably say something like:

   ... you need to define two apply method from the CanBuildFrom
   trait

or:

   ... you need to define two apply methods declared in the
   CanBuildFrom trait.

(The current wording sounds like it's saying that one needs to put
something in the CanBuildFrom trait.)

FIXED in 3ed 4th printing