The structure is definite in my opinion. A page in Roam should equate to a Tiddly. All the bullets (ie childs) in a Roam page should be grouped as normal text within the Tiddly. Insofar as child elements are nested in Roam, those should just translate to nested lists within the Tiddly.
@Saq's implementation is fundamentally correct I would say. I'm quite confident that vast majority of people importing from Roam would expect it to work this way -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/5cdfb3bf-083e-45e6-98a3-30ac443249c7%40googlegroups.com.

