There are quite a few comments on anotherquestion discussing the sentence 彼が持っているのは二百円です, in which the emphasis apparently falls on 二百円. I posted a comment asking if this could be explained as the pattern AはB emphasizing B rather than A, but I received the answer "No. Why?" I decided to delete my comment and create a separate question to discuss what I meant.
Here was my reasoning:
In Japanese: A Comprehensive Grammar, there's a section comparing は and が, which says the following (p.588):
When attached to the subject, ga emphasizes what precedes it, whereas wa focuses on what follows, i.e. pred. (in English, this difference can sometimes be captured by intonational stress).
In fact, it refers to は as a "focus particle" (p.577):
wa is a focus particle, but unlike mo (see 94), which focuses the N, etc. it is attached to, the basic function of wa is to focus on what follows, i.e. the pred.
Later, it describes a specific use of は, "marking known information" (p.580):
One function of wa, which is in keeping with its pred.-focusing effect, is to be attached to information that is already known or understood. In this use, wa has an effect similar to the English definite article (and other cases where a N refers to something known or previously mentioned).
So, in the sentence 彼が持っているのは二百円です, I interpreted は as marking a subject, and in particular, marking known information (彼が持っているの). This causes the focus to fall on the right half, as described above. I tried to express this generally as "the pattern AはB emphasizing B, not A".
Does this make sense? If not, can someone explain why it is wrong?