When the modeler has successfully met the criterion of replicating the model's ability to elicit the responses of relevance in a parallel context in the same amount of time and with the same quality, she or he is faced with the task of converting her or his behavioral competency (tacit knowledge into the form of an explicit model or representation (phase 4) and then to pass this explicitly coded set of patterns to naive users who have had no access to the original model. If, after assimilating the explicit model, the naive users' behavior closes on that of the original model, the explicated model is said to be adequate.
Your question concerns phase 4 - the actual coding. To code (or equivalently, to map) the tacit knowledge onto an explicit model involves the selection or development of the vocabulary, with either sensory grounded descriptors or operational definitions (which are explicit enough to allow the user to identify in the world of experience what is being referred by the various terms in the code or vocabulary) and its use to capture the various elements in the set of patterns that constitutes the explicit model (the explicit representation of the behavioral competency already achieved (phase 3).
Thus, the code is the set of explicit vocabulary items which describes the patterns (see Whispering (pages 53 and 54) for the three components in the presentation of any pattern).
Hope that this helps,