Handle nested table of contents

[atomic14]

Handle nested table of contents

[martinberlin]

I would make it easy:

1. Main category in bold
2. Sub-categories indentated two spaces right and normal font

Ex.

My main category
__ sub-category title

I've only seen so far books with 2 levels (Poetry book) and just flat 1 level. Maybe there are most complex examples. We can also not use indentation and just display main category in bold. But only if there is at least 2 levels, otherwise all in bold, will be too much.