Folding allows you to control the level of detail that you see in your outline.
- Use Command-. to collapse/expand items.
- Use . in outline mode to collapse/exand items.
- Click the triangle next to an item to toggle folding.
- See Atom > Edit > Folding for more folding commands and shortcuts.
Here I've folded the top level "Testing..." item.
Note that folding an item darkens the triangle handle.