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>
    <backlinks blcontinue="0|Main_Page|3080" />
  </query-continue>
  <query>
    <backlinks>
      <bl pageid="1513" ns="2" title="User:St/Sandbox My Sandbox" />
      <bl pageid="1543" ns="4" title="Apache OpenOffice Wiki:About" />
      <bl pageid="1604" ns="2" title="User:Jacqueline" />
      <bl pageid="1703" ns="1" title="Talk:Http://www.google.com/accounts/RP?c=CK-a v2ivt nkwEQuJ7l3OOzlpVu&amp;hl=lt" />
      <bl pageid="2152" ns="0" title="Extensions development" />
      <bl pageid="2165" ns="0" title="FR" />
      <bl pageid="2363" ns="0" title="Bibliographic/Developer Page/Current Implementation of the Bibliographic Component" />
      <bl pageid="2575" ns="10" title="Template:Language" />
      <bl pageid="2907" ns="0" title="Deutsche Übersetzung" />
      <bl pageid="2965" ns="2" title="User:St/Main Page" />
    </backlinks>
  </query>
</api>