To precede printable non-alphanumeric characters (e.g., *, $, ?) with the backslash ( \) escape character in a value string. When a non-alphanumeric character is quoted in a WFN, it SHALL be processed as string data. When a non-alphanumeric character is unquoted in a WFN, it may be interpreted as a special character by CPE 2.3 specifications, including this one.
Sources:
NISTIR 7696