A folder of a space as the site lists it: every folder of a repository, at any depth, gets the list of the notes filed under it, at the address a note of that path would take (<source>/<folder>/, <source>/<folder>/<sub>/), and yields to such a note; a space whose every note is dated gets a category per year and per month as well. The cards of the space page, the folders of the tree and the steps of the breadcrumb lead to the categories, which open as pages rather than unfold. A category is named by the title the folders block of its source declares, else by the folder name; its list counts the notes (note: Note) as their type words it and describes the type, or, below the top of the space, says how many pages are filed under the path.
Not to be confused with
A domain, which the folders may declare but which crosses (6 passages, no note) the sources (note: Source): a category is one folder of one repository (note: Knowledge repository), seen from its space.