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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>
    <pages>
      <page pageid="1" ns="0" title="Main Page">
        <links>
          <pl ns="0" title="GEOS-Chem 14.4.1" />
          <pl ns="0" title="GEOS-Chem Wiki archives" />
          <pl ns="0" title="GEOS-Chem in CESM" />
          <pl ns="0" title="GEOS-Chem model development priorities" />
          <pl ns="0" title="GEOS-Chem newsletters" />
          <pl ns="0" title="GEOS-Chem overview" />
          <pl ns="0" title="GEOS-Chem versions" />
          <pl ns="0" title="Software maintained by GEOS-Chem community members" />
        </links>
      </page>
    </pages>
  </query>
</api>