1. One or more computer-readable media storing executable instructions that when executed on a processor interface a first model with a second model, the media storing one or more instructions for: receiving a first instruction to load the second model, the second model loading in a manner that: allows the first model to access the second model via an executable component in the first model, and allows the first model to access the second model via the executable component when executable code in the second model has been modified; receiving a signal from the second model when the second model is loaded, the signal received in response to a second instruction received from the executable component in the first model; and passing the signal to the executable component in the first model when the second model is loaded, the signal passed to the executable component in the first model without making the executable code or the modified executable code of the second model available to a display that displays at least a portion of the first model, where the passing interfaces the first model with the second model.