IOS-解析HTML内容

怎么解析HTML文件？
在下面的代码中得到HTML文件， 只要BinarySecurityToken XML 节点之间数据。

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
 {
   if(_data)
  {
    //Here am getting the below HTML content
    NSString* content = [[NSString alloc] initWithData:_data
                                              encoding:NSUTF8StringEncoding];
  }
 }    
<input type="hidden" name="wa" value="wsignin1.0" />
<input type="hidden" name="wresult"
    value="<t:RequestSecurityTokenResponse xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust">
<t:Lifetime>
   <wsu:Created >2013-04-29T11:50:29.895Z</wsu:Created>
   <wsu:Expires>2013-04-29T12:00:29.895Z</wsu:Expires>
</t:Lifetime>
<wsp:AppliesTo>     
<EndpointReference>
<Address>urn:orin.converse</Address>
</EndpointReference></wsp:AppliesTo>
<t:RequestedSecurityToken>    
   <wsse:BinarySecurityToken>
         aHR0cCUzYSUyZiUyZnNjaGVtYWd0Sjk0JTNk
   </wsse:BinarySecurityToken>