The document discusses the grammatical structure "It was not until..." and provides examples of rewriting sentences using this structure. Some key points: - "It was not until..." is used to indicate that something did not happen or was not the case until a specific time. - Over 20 examples are given of sentences rewritten in the "It was not until..." form, with the time clause given. - Related structures like "Only when..." and "Not until..." are also discussed for inverting clauses.