When I have the text hello in my text block, the DOM tree looks like
<div contenteditable="true" class="st-text-block">
<p>
hello<br>
</p>
</div>
When I then select the text and add a link to http://google.de, the resulting DOM tree is
<div contenteditable="true" class="st-text-block">
<p>
<a href="http://google.de">
http://google.de
</a>
hello<br>
</p>
</div>