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="Conclusion" />
  </query-continue>
  <query>
    <alltransclusions>
      <t ns="10" title="Template:Bathing Your Chinchilla Cat" />
      <t ns="10" title="Template:Be gentle" />
      <t ns="10" title="Template:Before bringing a Chinchilla cat home, you should prepare your living space to ensure their safety and comfort." />
      <t ns="10" title="Template:Beneficial for their urinary tract health" />
      <t ns="10" title="Template:Caring for a Chinchilla cat is a commitment" />
      <t ns="10" title="Template:Cat-specific" />
      <t ns="10" title="Template:Chinchilla cat" />
      <t ns="10" title="Template:Chinchilla cats are known for their sweet, gentle, and affectionate nature." />
      <t ns="10" title="Template:Clean and tidy" />
      <t ns="10" title="Template:Common Health Issues" />
    </alltransclusions>
  </query>
</api>