~~~~ {#mycode .haskell .numberLines startFrom="100"}
qsort []     = []
qsort (x:xs) = qsort (filter (< x) xs) ++ [x] ++
               qsort (filter (>= x) xs)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# My header

~~~ {.text}
This is regular text. This is regular text.
~~~

~~~ {.quote}
> This is the first level of quoting.
>
> > This is nested blockquote.
>
> Back to the first level.
~~~

~~~ {data-id=test-123}
+   Red
+   Green
+   Blue
~~~

<h1 id="my-header">My header</h1>
<p class="text">This is regular text. This is regular text.</p>
<blockquote class="quote">
<p>This is the first level of quoting.</p>
<blockquote>
<p>This is nested blockquote.</p>
</blockquote>
<p>Back to the first level.</p>
</blockquote>
<ul data-id="test-123">
<li>Red</li>
<li>Green</li>
<li>Blue</li>
</ul>

# My header

This is regular text. This is regular text.
{: .text}

> This is the first level of quoting.
>
> > This is nested blockquote.
>
> Back to the first level.
{: .quote}

+   Red
+   Green
+   Blue
{: data-id="test-123"}

<h1 id="my-header">My header</h1>

<p class="text">This is regular text. This is regular text.</p>

<blockquote class="quote">
  <p>This is the first level of quoting.</p>

  <blockquote>
    <p>This is nested blockquote.</p>
  </blockquote>

  <p>Back to the first level.</p>
</blockquote>

<ul data-id="test-123">
  <li>Red</li>
  <li>Green</li>
  <li>Blue</li>
</ul>

# My header

~~~ {.as-markdown}
This is regular text. This is regular text.
~~~

~~~ {.as-markdown}
> This is the first level of quoting.
>
> > This is nested blockquote.
>
> Back to the first level.
~~~

~~~ {.as-markdown data-id=test-123}
+   Red
+   Green
+   Blue
~~~

~~~ haskell
main :: IO ()
~~~

#!/usr/bin/env runhaskell
import Text.Pandoc.Definition       (Pandoc(..), Block(..), Format(..))
import Text.Pandoc.Error            (handleError)
import Text.Pandoc.JSON             (toJSONFilter)
import Text.Pandoc.Options          (def)
import Text.Pandoc.Readers.Markdown (readMarkdown)

asMarkdown :: String -> [Block]
asMarkdown contents =
  case handleError $ readMarkdown def contents of
    Pandoc _ blocks -> blocks

-- | Unwrap each CodeBlock with the "as-markdown" class, interpreting
-- its contents as Markdown.
markdownCodeBlock :: Maybe Format -> Block -> IO [Block]
markdownCodeBlock _ cb@(CodeBlock (_id, classes, _namevals) contents) =
  if "as-markdown" `elem` classes then
    return $ asMarkdown contents
  else
    return [cb]
markdownCodeBlock _ x = return [x]

main :: IO ()
main = toJSONFilter markdownCodeBlock

<h1 id="my-header">My header</h1>
<p>This is regular text. This is regular text.</p>
<blockquote>
<p>This is the first level of quoting.</p>
<blockquote>
<p>This is nested blockquote.</p>
</blockquote>
<p>Back to the first level.</p>
</blockquote>
<ul>
<li>Red</li>
<li>Green</li>
<li>Blue</li>
</ul>
<div class="sourceCode"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">main ::</span> <span class="dt">IO</span> ()</code></pre></div>

#!/usr/bin/env runhaskell
import Text.Pandoc.Builder
import Text.Pandoc.JSON

webFormats :: [String]
webFormats =
  [ "html"
  , "html5"
  ]

script :: String -> Block
script src = Para $ toList $ rawInline "html" ("<script type='application/javascript'>" <> src <> "</script>")

injectScript :: Maybe Format -> Block -> IO Block
injectScript (Just (Format format)) cb@(CodeBlock (_id, classes, _namevals) contents) =
  if "web-script" `elem` classes then
    if format `elem` webFormats then
      return $ script contents
    else
      return Null
  else
    return cb
injectScript _ x = return x

main :: IO ()
main = toJSONFilter injectScript