[KevinH]

In general you use other semantics for front matter like "Prologue" or something less specific like "Front Matter". Typically a landmark semantic is placed on a specific single file. Some files may get assigned more than one landmark but each should target a separate specific id in that file where that landmark starts.

Things like marking Chapters is unneeded in Landmarks as the TOC lists those and aria-sections can label them if need be. Landmarks are the epub3 equivalent to epub2 guide items where semantic meaning is attached to specific files of interest to the user but those not normally included in a table of contents. Thus enabling a user to easily navigate to them too.