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>
    <alllinks galcontinue="R_Native_API" />
  </query-continue>
  <query>
    <pages>
      <page pageid="3" ns="0" title="Code Coverage Tool for R" />
      <page pageid="12" ns="0" title="Distributed Computing Working Group" />
      <page pageid="20" ns="0" title="Distributed Computing Working Group Progress Report 2016" />
      <page pageid="11" ns="0" title="Initial Survey of API Usage" />
      <page pageid="7" ns="0" title="Native API stats of R.h" />
      <page pageid="9" ns="0" title="Native API stats of Rinternals.h with USE R INTERNALS" />
      <page pageid="8" ns="0" title="Native API stats of Rinternals.h without USE R INTERNALS" />
      <page pageid="10" ns="0" title="Native API stats of all header files" />
      <page pageid="16" ns="0" title="R Certification" />
      <page pageid="15" ns="0" title="R Consortium and the R Community Code of Conduct" />
    </pages>
  </query>
</api>