grammar - AはB emphasizing B, rather than A

There are quite a few comments on another question 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?

Answer

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?

Yes, basically I agree... at least this is what I learned in 言語学概論(Basic Linguistics) class at college I think. I don't know if this would be any help but I remember learning something like this when I studied 情報構造(information structure), 旧情報・新情報(old/new information), 焦点(focus) etc.

私は山田です。---

When you're asked your name, you'll probably say 私は山田です, not 私が山田です, and you'll put the stress on 山田です. 私は part is the known/old information and 山田です is the new information and more important, so the focus is placed on 山田です.

私が山田です。---

When someone who doesn't know you is looking for you, asking 山田さんはどの人ですか?/誰が山田さん?, then you'll probably say 私が山田です, not 私は山田です, with a stress on 私が. You'll probably say the 私が with a slightly higher tone than 山田です. This time 山田 is the old information and 私 is the new information, and the focus falls on 私が, not on 山田です.

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There might be some cases where the focus falls on A in the pattern "AはB":

りんごを食べたのは 彼です。---

When you say りんごを食べたのは彼です (or 彼がりんごを食べました。) as a response to 誰がりんごを食べたの?/りんごを食べたのは誰?, you'll probably place a stress on 彼です, because 彼 is the new, more important information.

りんごを食べたのは 彼です。---

However, when you want to say "He ate the apple, but (it's not his fault, because) I made him eat it...", you might say りんごを食べたのは彼です。でも、食べさせたのは私です. Here, you'll place the stress on りんごを食べたのは, not on 彼です.