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="BlockBox|147" />
  </query-continue>
  <query>
    <pages>
      <page pageid="13" ns="0" title="Wiki" />
      <page pageid="65" ns="0" title="Biome" />
      <page pageid="69" ns="0" title="Block" />
      <page pageid="74" ns="0" title="Gebi Sand" />
      <page pageid="79" ns="0" title="Gebi Rock" />
      <page pageid="81" ns="0" title="Carved Stone" />
      <page pageid="88" ns="0" title="Gebi Bricks" />
      <page pageid="96" ns="0" title="Tiles" />
      <page pageid="100" ns="0" title="Sulfur Ore" />
    </pages>
  </query>
</api>