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 gatcontinue="Case_Study|611" />
  </query-continue>
  <query>
    <pages>
      <page pageid="602" ns="112" title="Studies:Alachua County Library District" />
      <page pageid="603" ns="112" title="Studies:Caledon Public Library" />
      <page pageid="604" ns="112" title="Studies:Cornell University Library" />
      <page pageid="605" ns="112" title="Studies:Duke University Library" />
      <page pageid="607" ns="112" title="Studies:ACRLMetrics" />
      <page pageid="608" ns="112" title="Studies:Florida Atlantic University Libraries" />
      <page pageid="609" ns="112" title="Studies:Federation of Ontario Public Libraries" />
      <page pageid="610" ns="112" title="Studies:Jacksonville Public Library" />
      <page pageid="904" ns="10" title="Template:CSS" />
      <page pageid="906" ns="118" title="CSS:CO menu blue" />
    </pages>
  </query>
</api>