Maple is a document authoring program that structures its projects as a hierarchical tree rather than a flat document. Although this is effectively equivalent to a standard directory/folder tree, Maple stores all of these in a single file. The project format is sometimes called Maple Tree. It seems to have used the extension ".mtr" early on, before switching to ".mpl".
- ↑ https://web.archive.org/web/20001012095612/http://shellfish.hotmail.ru/maplinfo.html
- ↑ Before 2006, at least, by which point the samples had switched away from it