constructor(upperContext) {
		/**
		 * The previous `ChainContext`
		 * @type {ChainContext}
		 */
		this.upper = upperContext;

		/**
		 * The number of choice contexts inside of the `ChainContext`.
		 * @type {number}
		 */
		this.choiceContextCount = 0;
	}
Creates a new instance.
@param {ChainContext} upperContext The previous `ChainContext`.