Support for Github "Alerts"

[Sajjon]

Describe your proposed improvement and the problem it solves. Seems this (great) tool does not render Github Markdown "alerts", as Github does.

Pandocs rendering

Githubs rendering

For this markdown:

> [!CAUTION]
> You **MUST** use the Rust programming language.

Using command:

pandoc --from=gfm --to=pdf -o PANDOC.pdf README.md

Would be nice to get the same kind of appearance as Github Markdown uses.

Describe alternatives you've considered. N/A

[Sajjon]

This is perhaps a duplicate of https://github.com/jgm/pandoc/issues/9716

[jgm]

No, it's not a duplicate of #9716, which concerns pandoc's markdown and not gfm. GitHub alerts are supported in gfm.

pandoc -f gfm -t native
> [!CAUTION]
> You **MUST** use the Rust programming language.
^D
[ Div
    ( "" , [ "caution" ] , [] )
    [ Div ( "" , [ "title" ] , [] ) [ Para [ Str "Caution" ] ]
    , Para
        [ Str "You"
        , Space
        , Strong [ Str "MUST" ]
        , Space
        , Str "use"
        , Space
        , Str "the"
        , Space
        , Str "Rust"
        , Space
        , Str "programming"
        , Space
        , Str "language."
        ]
    ]
]

The issue is that the writers don't by default do any special styling for this structure. See #9821 for a filter that may help with PDF output.

[jgm]

For background see also https://github.com/jgm/commonmark-hs/issues/132#issuecomment-1856751436