In-universe non-fiction work. If you read carefully, a second story or theme underlies it.
First edition was published 1 year before the Millennium Summer Sun Celebration. Interest was re-kindled after the famous events that occurred then, and the text has been updated and expanded to include commentary on events since then. Includes a mix of traditional legends and original fiction, followed by an analysis of the state of Equestrian science and/or history with respect to each story.