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 apcontinue="Distretti_sanitari_in_Puglia" />
  </query-continue>
  <query>
    <allpages>
      <p pageid="492" ns="0" title="Carte de santé" />
      <p pageid="632" ns="0" title="Cittadino UE" />
      <p pageid="631" ns="0" title="Cittadino extra-UE" />
      <p pageid="465" ns="0" title="Code STP" />
      <p pageid="196" ns="0" title="Codice ENI" />
      <p pageid="195" ns="0" title="Codice STP" />
      <p pageid="466" ns="0" title="Código STP" />
      <p pageid="41" ns="0" title="Distretti nel comune di Bari" />
      <p pageid="79" ns="0" title="Distretti nel comune di Roma" />
      <p pageid="163" ns="0" title="Distretti sanitari in Emilia Romagna" />
    </allpages>
  </query>
</api>