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>
    <alltransclusions atcontinue="Blueprint" />
  </query-continue>
  <query>
    <alltransclusions>
      <t ns="10" title="Template:Belgium" />
      <t ns="10" title="Template:Block CLD AUD" />
      <t ns="10" title="Template:Block Mobs" />
      <t ns="10" title="Template:Block eu time" />
      <t ns="10" title="Template:Block new features" />
      <t ns="10" title="Template:Block page views" />
      <t ns="10" title="Template:Block recent changes" />
      <t ns="10" title="Template:Block share" />
      <t ns="10" title="Template:Block tips" />
      <t ns="10" title="Template:Block welcome" />
    </alltransclusions>
  </query>
</api>