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>
    <allpages gapcontinue="Rule-Based_Computational_Modeling_of_Modular_Signaling_Protein_Interactions" />
  </query-continue>
  <query>
    <pages>
      <page pageid="144" ns="0" title="Robust multicellular computing using genetically-encoded NOR gates and chemical “wires”">
        <revisions>
          <rev />
        </revisions>
      </page>
      <page pageid="152" ns="0" title="Robustness in Nature: Challenges and Opportunities for the Systems Biology Community">
        <revisions>
          <rev />
        </revisions>
      </page>
    </pages>
  </query>
  <warnings>
    <revisions xml:space="preserve">Unrecognized value for parameter 'rvprop': content&quot;</revisions>
  </warnings>
</api>