Method set

lib/util/StackedMap.js:68–70

* Stores a value in the current layer, preserving explicit `undefined` * values with an internal marker. * @param {K} item the key of the element to add * @param {V} value the value of the element to add * @returns {void}

(item, value)

	 * @returns {void}
	 */
	set(item, value) {
		this.map.set(item, value === undefined ? UNDEFINED_MARKER : value);
	}

	/**
	 * Deletes a key from the current view, either by removing it outright in the