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="Frontal_arousal_rhythm_(average)_eegpedia.png|38" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Beta e double banana.png" />
      <f ns="6" title="File:Blink artifacts (average) eegpedia.png" />
      <f ns="6" title="File:Breach rhythm right centroparietal (double banana) eegpedia.png" />
      <f ns="6" title="File:Breathing artifact P4 in a intubated patient (source) eegpedia.png" />
      <f ns="6" title="File:Childhood absence epilepsy 4,5 year old girl (source) EEGpedia.png" />
      <f ns="6" title="File:EEG of the month 1(source).png" />
      <f ns="6" title="File:ESES in a 5.5-year-old girl (double banana) EEGpedia.png" />
      <f ns="6" title="File:FIRDA (source) EEGpedia.png" />
      <f ns="6" title="File:FOLDs (double banana).png" />
      <f ns="6" title="File:Frontal arousal rhythm, boy 4 years old eegpedia.png" />
    </allfileusages>
  </query>
</api>