States or containers may need inputs from the users or previous states (in an autonomous system) to undergo a transition. The information can be a sensor reading from the environment or a prioritization call based on the time taken for a task. They may also need to return specific information to other states or containers to allow the execution of those states. This information is described as input and output keys. Input keys are what a state may need for execution, so a state cannot manipulate what it receives (such as sensor information). Output keys are what the state returns as output to other states (such as prioritization calls) and can be manipulated. User data helps prevent errors and aids in debugging.