Each Zettel is associated with a unique ID, which is based on a timestamp of when the Zettel was created,
turned into a single number, but retaining most of its human-readability. For example, a Zettel created when
this comment was written would have the form (with dashes inserted for readability)
allows a Zettel to be created every second, which I think will be okay for real-world purposes.