"What they want to do is zero in on the protesters."
(The Guardian.)
What they want to do - a subject where "What" is a fused relative pronoun;
is - a linking verb;
zero in on the protesters - a complement where "zero in" is a phrasal verb.
Is my parsing acceptable?
What they want to do is zero in on the protesters. Yes, this is a fused relative construction, where the underlined element is a noun phrase functioning as subject. The infinitival clause zero in on the protesters is subjective predicative complement of "be".
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What they want to do is zero in on the protesters.
Yes, this is a fused relative construction, where the underlined element is a noun phrase functioning as subject.
The infinitival clause zero in on the protesters is subjective predicative complement of "be".
It's called a 'reversible' specifying construction because the subject and complement can be switched: