An instrument rack is a container device that can house multiple instruments (both stock and third party plugins) as well as insert fx after the instrument. You can layer multiple sounds to play at once in an instrument rack. These layers are known as chains. In this way you can have one clip of midi notes that send midi to multiple instruments. An instrument will also have 8 macro knobs, which allow you to map parameters from a nested device to the outer macro knobs.
An advanced trick in an instrument rack is to split the layers into zones so certain instruments only trigger at certain times.
Zones can be split by note range so higher notes play a different layer than lower notes.
Zones can also be split by velocity values so harder played notes will be a sent to a separate zone.
Lastly zones, also known as chains, can be split by “chain selector.” In this way, each individual chain can have its own value or range of values that it will be enabled. The orange chain selector value can be mapped to a macro knob so that you can have multiple instruments nested in a rack but be able to manage which one is on at a time. This can be very useful in a live performance scenario or even when producing (especially when you want various sounds to fire in rapid succession but only 1 or 2 at a time).