Document managing collections: folders, writability, the two-tab panel sources/ElementsCollection/ is the largest undocumented chunk found this session -- separate from elements_XML (the file format) and element_editor (drawing one element), nothing covered day-to-day collection management. The finding worth having written down: the common collection's read-only status is not a filesystem permissions check. ElementsLocation::isWritable() refuses anything under commonElementsDirN() unconditionally, by path -- that's why New folder/New element/rename/delete are greyed out there even running as an administrator, and why dragging an element out of the common collection copies it (there is no source to remove) while nothing can be rearranged inside it. Custom and company are genuinely writable; an embedded (project-internal) element follows the project's own read-only state. Also documents the panel's second tab -- Templates/macros, a reusable diagram-fragment mechanism distinct from single elements, drag-dropped onto a folio as a group -- and the full context-menu action set (new folder/element, edit, delete with a real not-undoable warning, reveal in file manager, reload from disk, the solo-folder filter, folder properties). Updates the Element Collections & Libraries stub in user_manual (EN/FR/DE) to link here instead of the placeholder bullets from the correction pass. EN/FR/DE.