TYPO3 Core

Any output add by an upgrade wizard using writeln() as recommended in the docs is written in one line because the whole output is only wrapped in:

<div class="callout-body">...</div>

To fix formatting, the out could be wrapped additionally in "pre" tags:

<div class="callout-body"><pre>.../pre></div>
</pre>
Alternatively, this could be added to the CSS for the ".callout-body" class:
<pre>
.callout-body {
  line-break: pre;
}
</pre>