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>
    <embeddedin eicontinue="10|Stub|1991" />
  </query-continue>
  <query>
    <embeddedin>
      <ei pageid="1631" ns="0" title="Super Mario 64" />
      <ei pageid="1812" ns="0" title="Super Mario Sunshine" />
      <ei pageid="1857" ns="0" title="Quake II" />
      <ei pageid="1903" ns="0" title="New Super Mario Bros. Wii" />
      <ei pageid="1971" ns="0" title="Metroid Prime/Speed Tricks" />
      <ei pageid="1972" ns="0" title="Metroid Prime/Boss Tricks" />
      <ei pageid="1973" ns="0" title="Metroid Prime/Version Differences" />
      <ei pageid="1974" ns="0" title="Metroid Prime/Secret Worlds" />
      <ei pageid="1987" ns="0" title="Metroid Prime 2: Echoes/Techniques" />
      <ei pageid="1989" ns="0" title="Metroid Prime 2: Echoes/Early Items" />
    </embeddedin>
  </query>
</api>