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>
    <blocks>
      <block id="1053" user="199.83.88.154" by="Matt" timestamp="2013-05-17T16:21:48Z" expiry="infinity" reason="Spamming links to external sites" anononly="" nocreate="" />
      <block id="1052" user="91.198.94.218" by="Matt" timestamp="2013-04-22T13:31:10Z" expiry="infinity" reason="Spamming links to external sites" anononly="" nocreate="" />
      <block id="1051" user="Amely" by="Matt" timestamp="2010-04-21T23:06:00Z" expiry="infinity" reason="Spamming links to external sites" nocreate="" autoblock="" noemail="" />
      <block id="1049" user="Sadfddssdfr" by="Matt" timestamp="2010-04-21T21:28:54Z" expiry="infinity" reason="Spamming links to external sites" nocreate="" autoblock="" />
      <block id="1047" user="Nexium sample" by="Matt" timestamp="2010-04-21T21:18:21Z" expiry="infinity" reason="" nocreate="" autoblock="" />
      <block id="1045" user="Viagra canadian source" by="Matt" timestamp="2010-04-21T18:59:57Z" expiry="infinity" reason="Spamming links to external sites" nocreate="" autoblock="" noemail="" allowusertalk="" />
      <block id="1043" user="Emg use xanax result" by="Matt" timestamp="2010-04-21T18:56:42Z" expiry="infinity" reason="" nocreate="" autoblock="" noemail="" allowusertalk="" />
      <block id="1041" user="Webhosting069" by="Matt" timestamp="2010-04-19T12:42:35Z" expiry="infinity" reason="Spamming links to external sites" nocreate="" autoblock="" noemail="" allowusertalk="" />
      <block id="1039" user="Katrinewhite79" by="Matt" timestamp="2010-04-12T00:05:28Z" expiry="infinity" reason="" nocreate="" autoblock="" noemail="" allowusertalk="" />
      <block id="1038" user="Novatedleasedeals" by="Matt" timestamp="2010-03-27T12:38:32Z" expiry="infinity" reason="Spamming links to external sites" nocreate="" autoblock="" noemail="" allowusertalk="" />
    </blocks>
  </query>
  <query-continue>
    <blocks bkstart="2010-03-27T12:37:50Z" />
  </query-continue>
</api>