Which phrase or clause offers incidental information that is not necessary for understanding the main sentence?

The phrase or clause that offers incidental information, which is not necessary for understanding the main sentence, is identified as nonrestrictive. Nonrestrictive elements are typically set off by commas and provide additional, but not essential, details. This means that if the nonrestrictive clause or phrase were removed from the sentence, the main point of the sentence would still remain clear and intact.

For instance, in the sentence "My brother, who lives in California, is visiting us," the clause "who lives in California" is nonrestrictive; it adds extra information about the brother but is not crucial for identifying him within the context of the sentence. In contrast, restrictive clauses are essential for defining the subject and generally do not use commas. Therefore, recognizing the nature of a nonrestrictive clause is critical for understanding how to convey additional information without confusing the primary message of a sentence.