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="Bosch_GST_150_CE.png|643" />
  </query-continue>
  <query>
    <pages>
      <page pageid="40" ns="3" title="User talk:Gustavo" />
      <page pageid="59" ns="3" title="User talk:Tomasdiez" />
      <page pageid="643" ns="14" title="Category:Hand tools" />
      <page pageid="704" ns="0" title="Bosch BKS4043 Wet &amp; Dry Handheld Vacuum Cleaner" />
      <page pageid="716" ns="0" title="Bosch GST 150 BCE Jigsaw" />
      <page pageid="739" ns="0" title="Bosch GEX 150 AC Orbit Sander" />
      <page pageid="971" ns="0" title="Laser Cutting" />
      <page pageid="1742" ns="0" title="3D PRINTING WITH ROBOTS" />
    </pages>
  </query>
</api>