A thread on Twitter led to this question from Joël de Bruijn: “Is an OPML file meant to encompass a whole library (with a notebook, subnotebook, note structure) or is it more like “one note = one OPML file” structure? Or something in between, what a user prefers?”
OPML is just a file format, like HTML or RSS. So it can be used for whatever you want, large files, small files, libraries, bullet charts, tree charts, graphs, calendars, directories, projects, things we haven’t invented yet.
It was originally designed as the interchange format for the outliner in Frontier, a scripting environment I created at UserLand Software in the late 80s and 90s. In Frontier, an outline could be a script, a menu, an object database, a blog, a blog post, or just an outline. We needed a way to exchange outlines with our product and other outliners, so this is