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"?>
    <allfileusages gafcontinue="B623d3dc1b8d59bc6053328551c3edbb.jpg|7038" />
      <page pageid="1958" ns="0" title="Gabriel Fallopio" />
      <page pageid="2672" ns="0" title="Basílica de San Pedro" />
      <page pageid="3146" ns="0" title="Inmaculada Concepción" />
      <page pageid="3300" ns="0" title="Devoción al Sagrado Corazón de Jesús" />
      <page pageid="8559" ns="0" title="Papa Juan Pablo I" />
      <page pageid="10419" ns="0" title="Intellectus Fidei" />
      <page pageid="12377" ns="0" title="Catequesis para niños: Alfabeto del niño Jesús" />
      <page pageid="12491" ns="0" title="Tiempos litúrigicos y solemidades" />
      <page pageid="14761" ns="0" title="Mano poderosa" />