Generalized raw attributes.
% pandoc -t native ```{=ms} .MACRO foo bar ``` ^D [RawBlock (Format "ms") ".MACRO\nfoo bar"]
% pandoc -t native Hi `there`{=ms}. ^D [Para [Str "Hi",Space,RawInline (Format "ms") "there",Str "."]]
% pandoc -t native ~~~ {=ms} .MACRO foo bar ~~~ ^D [RawBlock (Format "ms") ".MACRO\nfoo bar"]