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>
    <allredirects garcontinue="Bomba_del_setge_(s.XVII)|586" />
  </query-continue>
  <query>
    <pages>
      <page pageid="4" ns="0" title="Balma de la regullosa" />
      <page pageid="523" ns="0" title="El setge de 1645" />
      <page pageid="578" ns="0" title="Baluard de Sant Joan" />
      <page pageid="591" ns="0" title="Baluard de Sant Jordi" />
      <page pageid="600" ns="0" title="Baluard de Sant Andreu" />
      <page pageid="603" ns="0" title="Baluard de Sant Jaume" />
      <page pageid="605" ns="0" title="Barri hel.lenístic (Ciutadella)" />
      <page pageid="1282" ns="0" title="Pení" />
      <page pageid="4228" ns="0" title="Biblioteca municipal" />
      <page pageid="4517" ns="0" title="Les cases dels pescadors" />
    </pages>
  </query>
</api>