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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.
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<?xml version="1.0"?>
<api>
  <query-continue>
    <alltransclusions gatcontinue="Marco_Pagan_Books" />
  </query-continue>
  <query>
    <pages>
      <page pageid="71" ns="10" title="Template:Contrib" />
      <page pageid="6460" ns="10" title="Template:Digby Smith Books" />
      <page pageid="89" ns="10" title="Template:French Army References" />
      <page pageid="824" ns="10" title="Template:French Drummer with Royal Livery" />
      <page pageid="6425" ns="10" title="Template:French Gendarmerie Service" />
      <page pageid="6462" ns="10" title="Template:Germania Figuren" />
      <page pageid="115" ns="10" title="Template:Hanoverian Army References" />
      <page pageid="125" ns="10" title="Template:Hesse-Kassel Army References" />
      <page pageid="474" ns="10" title="Template:Hungarian Line Infantry Colours" />
      <page pageid="6240" ns="10" title="Template:Map of Schweidnitz" />
    </pages>
  </query>
</api>