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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.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allimages gaicontinue="Adnatosphaeridium_caulleryi.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="13948" ns="6" title="File:Achilleodinium.jpg">
        <duplicatefiles>
          <df name="Achilleodinium_biformoides.jpg" user="Maintenance script" timestamp="2015-09-01T05:28:56Z" />
        </duplicatefiles>
      </page>
      <page pageid="13985" ns="6" title="File:Achilleodinium biformoides.jpg">
        <duplicatefiles>
          <df name="Achilleodinium.jpg" user="Maintenance script" timestamp="2015-09-01T05:28:53Z" />
        </duplicatefiles>
      </page>
      <page pageid="14322" ns="6" title="File:Achomosphaera alcicornu.jpg" />
      <page pageid="14117" ns="6" title="File:Achomosphaera andalousiensis.jpg" />
      <page pageid="14801" ns="6" title="File:Achomosphaera crassipellis.jpg" />
      <page pageid="14160" ns="6" title="File:Achomosphaera neptuni.jpg" />
      <page pageid="13907" ns="6" title="File:Achomosphaera sagena.jpg" />
      <page pageid="13913" ns="6" title="File:Acti115.gif">
        <duplicatefiles>
          <df name="Acti177.gif" user="Maintenance script" timestamp="2015-09-01T05:29:04Z" />
        </duplicatefiles>
      </page>
      <page pageid="14087" ns="6" title="File:Acti177.gif">
        <duplicatefiles>
          <df name="Acti115.gif" user="Maintenance script" timestamp="2015-09-01T05:28:50Z" />
        </duplicatefiles>
      </page>
      <page pageid="13977" ns="6" title="File:Adnatosphaeridium.jpg">
        <duplicatefiles>
          <df name="Adnatosphaeridium_vittatum.jpg" user="Maintenance script" timestamp="2015-09-01T05:29:35Z" />
        </duplicatefiles>
      </page>
    </pages>
  </query>
</api>