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>
    <pageswithprop pwpcontinue="90" />
  </query-continue>
  <query>
    <pageswithprop>
      <page pageid="3" ns="0" title="Main Page" value="WikiOverland" />
      <page pageid="8" ns="0" title="Peru" value="Overland Peru Travel" />
      <page pageid="9" ns="0" title="Ecuador" value="Overland Ecuador Travel" />
      <page pageid="11" ns="10" title="Template:Metadata country" value="Overland Metadata country Travel" />
      <page pageid="12" ns="0" title="Country template" value="Overland Country template Travel" />
      <page pageid="21" ns="0" title="El Salvador" value="Overland El Salvador Travel" />
      <page pageid="24" ns="0" title="Argentina" value="Overland Argentina Travel" />
      <page pageid="83" ns="0" title="Bolivia" value="Overland Bolivia Travel" />
      <page pageid="88" ns="0" title="Panama" value="Overland Panama Travel" />
      <page pageid="89" ns="0" title="Costa Rica" value="Overland Costa Rica Travel" />
    </pageswithprop>
  </query>
</api>