Quite handy in Eclipse. Is there a similar feature in Atom?
Yes, in Atom they’re called Markers and Decorators. You can find documentation about the API here:
I think he’s actually talking about the markers next to the scrollbar on the right, and AFAIK there’s no such thing currently, but you can get something approaching using the highlight-selected package combined with minimap and minimap-highlight-selected.
If I remember correctly, these are essentially linting highlights.
Another great idea for a PR on the Linter package responsible for the language of your choice.