The AP Stylebook prescribes its use by wire reporters (in a "keyword slugline") as follows: "The keyword or slug (sometimes more than one word) clearly indicates the content of the story." Sometimes a slug also contains code information that tells editors specific information about the story — for example, the letters "AM" at the beginning of a slug on a wire story tell editors that the story is meant for morning papers, while the letters "CX" indicate that the story is a correction to an earlier story.
The AP Stylebook recommends its application by wire reporters (in a "keyword slugline") in this context: "A keyword or slug (which can be one or more words) clearly conveys the main topic of the article." Sometimes, a slug also includes coding information that provides editors with specific details about the story — such as the letters "AM" at the start of a wire story slug, indicating it's meant for morning publications, and "CX" denoting a correction to an earlier piece.