[zeveb]

> For example, Hacker News nested comments are displayed as being on one level.

I think that this is because syntactically they are on the same level. Assuming I'm reading the source correctly, they're all cells in a table, at the same level, rather than being nested.

So elinks et al. are correct; the site is using CSS to indicate something not in the structure.

[Programmatic]

What would be the correct way to structure something like this in pure HTML?

[krapp]

Ordered and unordered lists (<OL|UL><LI></LI></OL|UL>) were pretty much intended for this.