Indented Hierarchy Rows

This is:

- [ ] ~~a bug report~~
- [X] a feature request
- [X] **not** a usage question

I would need the "indented hierarchy" feature, but did not find it in the PhpSpreadsheet documentation, so I thought I would file a feature request.

Do you think it might be possible to add it? I really don't know the level of complexity of such a feature.

Bonus question: maybe it could be possible to "insert raw formatting code" (I don't even know if it's a thing... just asking, at the risk of looking like an idiot)