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 afcontinue="Integration_graphique.svg|107" />
  </query-continue>
  <query>
    <allfileusages>
      <f fromid="107" ns="6" title="Fichier:Ballon reflux flexion deformee.svg" />
      <f fromid="1" ns="6" title="Fichier:Boiteamail.jpg" />
      <f fromid="152" ns="6" title="Fichier:Boiteamail.jpg" />
      <f fromid="21" ns="6" title="Fichier:Cmac.jpg" />
      <f fromid="21" ns="6" title="Fichier:Colored neural network.svg" />
      <f fromid="21" ns="6" title="Fichier:Estimation of Distribution Algorithm animation.gif" />
      <f fromid="21" ns="6" title="Fichier:Fig 2 The iteration of the number of components in intellectual systems.jpg" />
      <f fromid="21" ns="6" title="Fichier:Fig 3 Emergence of info-interaction and evolution of ICT within populations of Humanity.jpg" />
      <f fromid="107" ns="6" title="Fichier:Integral.svg" />
      <f fromid="107" ns="6" title="Fichier:Integral example.png" />
    </allfileusages>
  </query>
</api>