Related to Zettelksaten: if you want to follow the Folgezettel ID system, you may find helpful the ability to manage notes in the sidebar as a nested list without using Folders structure. This would allow you to expand or collapse sections and sub-sections in order to improve the way to view and work with the different branches
It is not about a list within the note but about managing notes as a nested list
Since there is no database, just folders of files, what would you propose the entity at the top of each nest would be? Is 1a1 Title a file? A folder? Some internal fiction that Obsidian sees but is not reflected in the external data in a vault?
afaics, the easiest way of achieving something similar would be through links. Either a normal link in a special place (YAML?), or a special syntax ([[[ ?), with the requested display through a plugin.
Otherwise has to be a plugin with database. Either way a plugin, not a feature.
