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>
    <allpages>
      <p pageid="3" ns="0" title="Configurando Clientes de E-Mail" />
      <p pageid="20" ns="0" title="Configurando clientes de email iOS7" />
      <p pageid="27" ns="0" title="Outlook:mac 2011" />
      <p pageid="4" ns="0" title="Outlook 2013" />
      <p pageid="1" ns="0" title="Página principal" />
      <p pageid="9" ns="0" title="Redirecionamento de Mensagens" />
    </allpages>
  </query>
</api>