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>
    <allpages>
      <p pageid="154" ns="0" title="BEAUTY 2013" />
      <p pageid="225" ns="0" title="BF2013" />
      <p pageid="152" ns="0" title="BLV2013" />
      <p pageid="283" ns="0" title="BNL 2013 Top10" />
      <p pageid="365" ns="0" title="BNL Link to Nobel Prize" />
      <p pageid="238" ns="0" title="BPS 2013" />
      <p pageid="377" ns="0" title="Belle II" />
      <p pageid="375" ns="0" title="Bilas Pal" />
      <p pageid="325" ns="0" title="Bill Morse" />
      <p pageid="366" ns="0" title="Breakthrough Prize 2016" />
    </allpages>
  </query>
  <query-continue>
    <allpages apcontinue="Breakthrough_of_2012" />
  </query-continue>
</api>