Which type of information is NOT generally regarded as a "supporting detail"?

The correct answer identifies the author's opinion without any factual backing as a type of information that is not generally regarded as a "supporting detail." Supporting details are meant to back up or clarify the main idea of a piece of writing. They typically include concrete evidence, such as statistical data, examples, and expert testimony, all of which help to establish credibility and provide a foundation for the author's claims.

In contrast, an author's opinion without factual backing lacks the necessary support to reinforce the main idea. Without evidence or reasoning, such opinions may be subjective and not universally accepted or verifiable. Thus, they do not fulfill the role of a supporting detail, which is to strengthen arguments or enhance the reader's understanding of the topic at hand.