The Codes in the Codebook, in the order they appear in the Codebook.
Codebooks are tree structured and may be of any depth, although a depth of more than 6 is rare.
Only the leaf nodes may be applied to a response. These leaf nodes are Codes.
Nets have child codes or nets. Nets may not be used to code a response. They serve to provide structure to the Codebook.
Nets typically represent groups of related codes.