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="Diving_Areas" />
  </query-continue>
  <query>
    <pages>
      <page ns="10" title="Template:CMAS Diving Courses" missing="" />
      <page ns="10" title="Template:DDI Diving Courses" missing="" />
      <page pageid="155" ns="10" title="Template:Contact Details" />
      <page pageid="9830" ns="10" title="Template:Coords Format" />
      <page pageid="9842" ns="10" title="Template:Corinthian Gulf Areas" />
      <page pageid="9843" ns="10" title="Template:Corinthian Gulf Schools" />
      <page pageid="9844" ns="10" title="Template:Crete Areas" />
      <page pageid="9845" ns="10" title="Template:Crete Schools" />
      <page pageid="9833" ns="10" title="Template:Cyclades Areas" />
      <page pageid="9834" ns="10" title="Template:Cyclades Schools" />
    </pages>
  </query>
</api>