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>
    <alltransclusions gatcontinue="Building_levels|254" />
  </query-continue>
  <query>
    <pages>
      <page pageid="5" ns="10" title="Template:Boxlayout1" />
      <page pageid="11" ns="0" title="Pagina principale" />
      <page pageid="12" ns="4" title="Xhodon:Portale comunità" />
      <page pageid="87" ns="0" title="Albero della vita" />
      <page pageid="238" ns="0" title="Albero della Vita" />
      <page pageid="239" ns="0" title="Scuola delle erbe" />
      <page pageid="248" ns="0" title="Grotta dei cristalli" />
      <page pageid="250" ns="0" title="Radice delle pietre" />
      <page pageid="251" ns="0" title="Filone della resina" />
      <page pageid="252" ns="0" title="Grotta Segreta" />
    </pages>
  </query>
</api>