br

sundown.php

<?php
$render = new \Sundown\Render\HTML();
$md = new \Sundown\Markdown($render, array("autolink"=>true));

$stringOfDeath = <<<EOD

``` yaml
#someLabel
some code text
```


Testing inline markup for code ```triple tick text```
EOD;

echo $md->render($stringOfDeath);
$extensions = $md->getExtensions();
var_dump($extensions);

~ php sundown.php

``` yaml

someLabel

some code text ```

Testing inline markup for code triple tick text

array(1) {
'autolink' =>
bool(true)
}

~ php sundown.php 
<p>``` yaml</p>
<h1>someLabel</h1>
<p>some code text
```</p>
<p>Testing inline markup for code <code>triple tick text</code></p>
array(1) {
  'autolink' =>
  bool(true)
}

you need to activate the fenced code blocks if you want the GFM syntax for code blocks.
Otherwise, when using standard markdown, they need to be indented