Sorry to respond so late, but this is the first time I've looked at this when my brain isn't completely fuzzy from lack of sleep. I'm going to talk myself through the first para., to see if I can get down to what it really means. I will assume for this purpose that "this" book has only one darned edition. (Those extra qualifiers really get in my way!)
<<<<Without limiting the meaning of the expression reasonable portion in this Act, where a literary, dramatic or musical work (other than a computer program) is contained in a published edition of that work, being an edition of not less than 10 pages, a copy of part of that work, as it appears in that edition, shall be taken to contain only a reasonable portion of that work if the pages that are copied in the edition:
Okay; I'm pretty sure this means, essentially: You have a book that is at least ten pages long. The part(s) you copy will only be considered to be a reasonable portion if:
Okay, (a)is pretty simple: you copy 10% or less of the number of pages.
(b)in a case where the work is divided into chapters exceed, in the aggregate, 10% of the number of pages in that edition but contain only the whole or part of a single chapter of the work
Maybe: you copy more than 10% of the total number of pages, but these are confined to one chapter only.
I don't remember who I might agree or disagree with; but this is how it reads to me.
