330. The State of the Turn is partially determined by whether or not the Chain currently exists.

330.1. The turn is said to be in a Closed State if a Chain exists.

330.1.a. Cards of all Categories, by default, cannot be played during a Closed State.
330.1.b. Card abilities, by default, cannot be played during a Closed State.

330.2. The turn is said to be in an Open State if no Chain exists.