You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <alllinks galcontinue="Contao.Dev_ExtensionsCatalogMailer" />
  </query-continue>
  <query>
    <pages>
      <page ns="0" title="Back end" missing="" />
      <page ns="0" title="Benutzer:BugBuster" missing="" />
      <page ns="0" title="Benutzer:Lucina" missing="" />
      <page ns="0" title="CatalogExt" missing="" />
      <page pageid="117" ns="0" title="Banner" />
      <page pageid="118" ns="0" title="Banner Update v1 to v2" />
      <page pageid="22" ns="0" title="Beginner" />
      <page pageid="88" ns="0" title="Bot Detection" />
      <page pageid="9" ns="0" title="Chat HowTo" />
      <page pageid="383" ns="0" title="Contao.Dev ExtensionsCatalogExt" />
    </pages>
  </query>
</api>