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>
    <pages>
      <page pageid="101" ns="0" title="Basic GitHub Tutorial" />
      <page pageid="3" ns="0" title="Frequency Tuning" />
      <page pageid="38" ns="0" title="Gain Control" />
      <page pageid="85" ns="0" title="Polarization Mixing Correction (Old)" />
      <page pageid="25" ns="0" title="System Gain Calibration" />
      <page pageid="7" ns="0" title="Total Power Calibration" />
    </pages>
  </query>
</api>