TouchXML namespace resolving?

I am trying to parse the following XML via TouchXML:

<s:Envelope xmlns:s="namespace_1">
   <s:Body>
      <DefinedEntitiesResponse xmlns="namespace_2">
         <DefinedEntitiesResult xmlns:a="namespace_3" xmlns:i="namespace_4">
            <a:DefinedEntity>
               <a:Description>Some Description</a:Description>
               <a:Name>Some entity name</a:Name>
            </a:DefinedEntity>
         </D开发者_如何学编程efinedEntitiesResult>
      </DefinedEntitiesResponse>
   </s:Body>
</s:Envelope>

I try to parse this like so:

CXMLDocument *doc = [[[CXMLDocument alloc] initWithXMLString:[request responseString] options:0 error:nil] autorelease];

NSArray *resultNodes = [doc nodesForXPath:@"/s:Envelope" error:nil];
NSLog(@"Resultnodes: %@", resultNodes);

And getting the error:

XPath error : Undefined namespace prefix
XPath error : Invalid expression

Question 1: What am I doing wrong? Question 2: Should I use TouchXML as a library, or is there something that works easier and better?

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Use the following project on github to parse your XML into NSDictionary. You can then use NSPredicate to look up values in the parsed dictionary.