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>
    <allimages gaicontinue="Fig1.31_Two_Levels_of_ICMP_Encapsulation.gif" />
  </query-continue>
  <query>
    <pages>
      <page pageid="598" ns="6" title="File:AH Header Format.gif" />
      <page pageid="643" ns="6" title="File:AH Position in IPv4 and IPv6.gif" />
      <page pageid="641" ns="6" title="File:ESP Header Format.gif" />
      <page pageid="644" ns="6" title="File:ESP Position in IPv4 and IPv6.gif" />
      <page pageid="717" ns="6" title="File:Ethernet fields values.gif" />
      <page pageid="716" ns="6" title="File:Ethernet frame with payload.gif" />
      <page pageid="719" ns="6" title="File:Ethernet payload for PPPoE.gif" />
      <page pageid="395" ns="6" title="File:Fig1.11 ARP Transmission Sequence.gif" />
      <page pageid="396" ns="6" title="File:Fig1.12 ARP Message.gif" />
      <page pageid="397" ns="6" title="File:Fig1.21 Special Forms of IP Addresses.gif" />
    </pages>
  </query>
</api>