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="Caution|630" />
  </query-continue>
  <query>
    <pages>
      <page pageid="5" ns="0" title="Core from Subversion" />
      <page pageid="9" ns="0" title="Chat HowTo" />
      <page pageid="24" ns="12" title="Help:Contents" />
      <page pageid="30" ns="0" title="Xing" />
      <page pageid="86" ns="0" title="Visitors" />
      <page pageid="117" ns="0" title="Banner" />
      <page pageid="383" ns="0" title="Contao.Dev ExtensionsCatalogExt" />
      <page pageid="413" ns="0" title="Contao.Dev ExtensionsFormauto" />
      <page pageid="422" ns="0" title="Contao.Dev ExtensionsCatalog" />
      <page pageid="679" ns="10" title="Template:C2g" />
    </pages>
  </query>
</api>