Here's a subtopic
So runs of '=='s to format heading levels works.
But maybe you want to have subpages (that by default aren't Flow boards) if you're trying to make structured wiki pages.
Here's a deeper subtopic
But presumably someone trying to respond to this one section would get frustrated. They could use VE to copy and paste and italicize the original text. Sort of like trying to reply to an e-mail message by selective quoting.
FWIW my biased suggestion is to make "Quote the selection in a new reply" and "Create a new topic from the selection" very easy, kind of how Phabricator's 'Quote' generates a link back like this:
- >>! In T94279#1160023, @SomeUser wrote:
- > (Their text)
However, my idea doesn't have much traction :)
We can even go big with H1
A Flow post allows most wiki markup, even though some doesn't make sense.