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>
    <allfileusages afcontinue="Block_of_Green_Hexorium_Crystal.png" />
  </query-continue>
  <query>
    <allfileusages>
      <f ns="6" title="File:Basic Conversion Computer.png" />
      <f ns="6" title="File:Black Hexorium Crystal.png" />
      <f ns="6" title="File:Black Hexorium Dye.png" />
      <f ns="6" title="File:Black Hexorium Monolith.png" />
      <f ns="6" title="File:Black Hexorium Nether Monolith.png" />
      <f ns="6" title="File:Black Hexorium Nether Ore.png" />
      <f ns="6" title="File:Black Hexorium Ore.png" />
      <f ns="6" title="File:Black Hexorium Wafer.png" />
      <f ns="6" title="File:Block of Black Hexorium Crystal.png" />
      <f ns="6" title="File:Block of Blue Hexorium Crystal.png" />
    </allfileusages>
  </query>
</api>