The carat symbol indicates where something must be:

The carat symbol, often represented as a small upward-pointing triangle (^), is commonly used in editing and proofreading to indicate a position where something should be inserted into a text. This symbol serves as a visual cue for the editor or writer to add content at a specified location within the document.

For instance, if a writer realizes that a word or phrase is missing in a sentence, placing a carat symbol in the appropriate spot is a conventional way to denote where that insertion needs to take place. In contrast, the other answer choices pertain to different types of editing actions. Highlighting refers to marking text for emphasis or attention, revising involves changing existing content, and deleting indicates the removal of text. However, the specific function of the carat symbol is tied exclusively to insertion within written documents.