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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>
    <allredirects garcontinue="List_of_diagnostics_archived_to_bpch_format|1284" />
  </query-continue>
  <query>
    <pages>
      <page pageid="179" ns="0" title="Emissions overview" />
      <page pageid="202" ns="0" title="Version control with Git" />
      <page pageid="208" ns="0" title="Using Git with GEOS-Chem" />
      <page pageid="1582" ns="0" title="GEOS-Chem v11-03" />
      <page pageid="1583" ns="0" title="GEOS-Chem v11-03 benchmark history" />
      <page pageid="1708" ns="0" title="GEOS-Chem coding style guide" />
      <page pageid="1795" ns="0" title="Benchmark/" />
      <page pageid="2077" ns="0" title="Benchmark/GEOS-Chem 13.0.0" />
      <page pageid="2181" ns="0" title="Emissions and Deposition Working Group" />
      <page pageid="2273" ns="0" title="GEOS-Chem Adjoint" />
    </pages>
  </query>
</api>