That's Haddock markup (though the ## one is new for me):
https://www.haskell.org/haddock/doc/html/ch03s08.html

On 4 May 2017 at 18:10, Jeffrey Brown <jeffbrown.the@gmail.com> wrote:
> I am looking at Text.Markdown. The Types.hs file[1] looks like it's got
> comments that are meant to be viewed as some form other than plain text --
> for instance,
>
>     , msAddHeadingId :: Bool
>       -- ^ If @True@, an @id@ attribute is added to the heading tag with the
> value equal to
>       -- the text with only valid CSS identifier characters.
>       --
>       -- > ## Executive Summary
>       --
>       -- > <h2 id="executive-summary">Executive Summary</h2>
>       --
>       -- Default: @False@
>       --
>       -- Since 0.1.13
>
> I thought it might be literate Haskell, but the file ends in .hs, not .lhs.
>
> How should I view it? Preferably in Emacs?
>
> [1] https://github.com/snoyberg/markdown/blob/master/Text/Markdown/Types.hs
>
> --
> Jeff Brown | Jeffrey Benjamin Brown
> Website   |   Facebook   |   LinkedIn(spammy, so I often miss messages here)
> |   Github
>

> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

--
Ivan Lazar Miljenovic
Ivan.Miljenovic@gmail.com
http://IvanMiljenovic.wordpress.com