Collapse all by level: not working in one file

Not sure if this is relevant here, but one source of confusion can be that the TaskPaper format is a purely tab-indented outline.

In the following example, Beta, Gamma and Delta are not children of Alpha (they are peers), and will not be collapsed under it:

Alpha:
- Beta
- Gamma
- Delta

(only tab-indented items are children of preceding project lines. If the project is itself indented, only items that are more indented descend from it)

See the example at:

https://www.taskpaper.com/guide/getting-started/