More precisely, do this for nested flows with the "refcontent" style.
For instance this Scribble:
@margin-note{Note: This is a note. Let's make it long enough that the
markdown output will have to line-wrap, to make sure the > mark starts
each line properly.}
Will render as this Markdown:
> Note: This is a note. Let's make it long enough that the markdown output
> will have to line-wrap, to make sure the > mark starts each line
> properly.
A site like GitHub.com will render this in a block-quote style
suitable for notes:
> Note: This is a note. Let's make it long enough that the markdown output
> will have to line-wrap, to make sure the > mark starts each line
> properly.