Method _flatten

lib/util/LazySet.js:79–82

* Flattens any nested lazy sets that were queued for merging.

()

	 * Flattens any nested lazy sets that were queued for merging.
	 */
	_flatten() {
		flatten(this._toMerge, this._toDeepMerge);
		this._toDeepMerge.length = 0;
	}

	/**
	 * Materializes all deferred additions into the backing set.