Tabsets in markdown not working

[nhward]

I have been struggling for some time now trying to get a markdown document whose headings utilise {.tabset} to process through markdown::mark_html() with its tabs functioning correctly.

In brief:
I can preview in RStudio (i.e. knit) the markdown and show that the tabs are working correctly so I am confident that the document is correct.
When I process this markdown document (via mark_html()) and show it in a modal dialogue, the tabs are reduced to headings. Does one of the options allow this?

Is this something that I should be able to do? Please tell me if I am wasting my time.

I have tried using rmarkdown::render() but this is producing full documents whereas I am wanting a snippet to embed.