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="CESG" />
  </query-continue>
  <query>
    <allpages>
      <p pageid="1422" ns="0" title="Bamberg, Staatsbibliothek, lit. 25 (olim Ed.IV.11)" />
      <p pageid="1552" ns="0" title="Benevento, Archivio Capitolare, V 19" />
      <p pageid="1553" ns="0" title="Benevento, Archivio Capitolare, V 20" />
      <p pageid="1420" ns="0" title="Berlin, Staatsbibliothek zu Berlin Preußischer Kulturbesitz, Mus. 40047" />
      <p pageid="1358" ns="0" title="Bologna, Museo internazionale e biblioteca della musica" />
      <p pageid="1544" ns="0" title="Budapest, Egyetemi Könyvtár, lat. 118" />
      <p pageid="1545" ns="0" title="Budapest, Egyetemi Könyvtár, lat. 119" />
      <p pageid="1546" ns="0" title="Budapest, Egyetemi Könyvtár, lat. 121" />
      <p pageid="1547" ns="0" title="Budapest, Egyetemi Könyvtár, lat. 122" />
      <p pageid="221" ns="0" title="CEEC" />
    </allpages>
  </query>
</api>