What is the purpose of the pronoun 'it' here? Is it merely a dummy pronoun, a semantically empty subject? Or is it a cataphoric pronoun, serving as a placeholder for the extraposed infinitival clause?
It was their turn to be surprised.
If the former, then why? That is, why is it possible to use a dummy pronoun in this sentence? I thought that the uses of 'it' as a dummy pronoun were limited to clauses expressing time ("It's two o'clock"), date ("It's Thursday"), or weather ("It's raining"). Assuming that 'it' is indeed a dummy pronoun here (which I think likely), then is its use idiomatic?
Some enlightenment would be appreciated.