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>
    <allfileusages gafcontinue="Environmental_portal_lussemburgo.png" />
  </query-continue>
  <query>
    <pages>
      <page ns="6" title="File:Embed Geonorge.png" missing="" />
      <page pageid="434" ns="6" title="File:Barrastrumenti.png" />
      <page pageid="337" ns="6" title="File:Ckan1.jpg" />
      <page pageid="338" ns="6" title="File:Ckan2.png" />
      <page pageid="102" ns="6" title="File:Consumatori.png" />
      <page pageid="172" ns="6" title="File:Create new project rstudioserver.png" />
      <page pageid="174" ns="6" title="File:Create new project rstudioserver 01.png" />
      <page pageid="353" ns="6" title="File:Data catalogue lussemburgo.png" />
      <page pageid="418" ns="6" title="File:Displacement issue.png" />
      <page pageid="229" ns="6" title="File:EDIT MD.png" />
    </pages>
  </query>
</api>