The sentence pattern similar to...is that...is an appositive clause or a slogan clause, such as What he sa

What you are talking about is not a clause, but a form of expression. As for what he said is that..., is is the predicate verb that takes over the previous subject clause, and that is the predicate verb that takes over. The following object. The "that" in the latter sentence may be followed by a predicative clause, which also needs to be viewed based on the entire sentence.

Appositive clauses are separated by commas before and after, and there is no other component other than a comma between them and the modifying component. So it cannot be an appositive.