1. Rules or principles for determining a diagnostic code when using diagnostic code books such as each space, typefaces, indentations, punctuation marks, instructional notes, abbreviations, cross-reference notes, and specific usage of the words and, with, and due to. These rules assist in the selection of correct codes for the diagnoses encountered. Also called coding conventions. 2. Space-saving rule used in the “Index,” which is the last section of the annually published Current Procedural Terminology code book. For example:KneeIncision (of)In this example, the word in parentheses (of) does not appear in the Index, but it is inferred. As another example:PancreasAnesthesia (for procedures on)In this example, because there is no such entity as pancreas anesthesia, the words in parentheses are inferred (i.e., anesthesia for procedures on the pancreas).