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="Green|1710" />
  </query-continue>
  <query>
    <pages>
      <page pageid="1518" ns="0" title="ConfigurationCompilerLibrary" />
      <page pageid="1520" ns="0" title="OldConfigurationMigration" />
      <page pageid="1535" ns="0" title="OldConfigurationConditions" />
      <page pageid="1537" ns="0" title="Installing Microsoft C compiler (Visual Studio 2010 and older, or Windows SDK 7.1 and older)" />
      <page pageid="1680" ns="0" title="ProposalProjectFiles" />
      <page pageid="1838" ns="0" title="GUI Capture (Developement)" />
      <page pageid="1840" ns="0" title="GUI Replay (Developement)" />
      <page pageid="2298" ns="0" title="Installing Microsoft C compiler 6.1 and older" />
      <page pageid="2343" ns="0" title="Testing Tool (Architecture)" />
      <page pageid="2533" ns="0" title="Unicode Free Operator" />
    </pages>
  </query>
</api>