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>
    <backlinks>
      <bl pageid="1495" ns="0" title="Bert Winiford Wilson" />
      <bl pageid="1526" ns="0" title="William B. Heeter" />
      <bl pageid="1573" ns="0" title="Tree: James Elgie Beals" />
      <bl pageid="1576" ns="0" title="Tree: Winnifred May Kline" />
      <bl pageid="1577" ns="0" title="Tree: John Duncan Williams" />
      <bl pageid="1578" ns="0" title="Tree: Corinna Brady Lowder" />
      <bl pageid="1579" ns="0" title="Tree: Mack Herron King" />
      <bl pageid="1581" ns="0" title="Tree: Bert Winiford Wilson" />
      <bl pageid="1582" ns="0" title="Tree: Clara Mabel Wimer" />
      <bl pageid="2796" ns="0" title="Tree: Nancy Grace Thomas" />
    </backlinks>
  </query>
  <query-continue>
    <backlinks blcontinue="0|Main_Page|5265" />
  </query-continue>
</api>