XML DTD parsing - foundElementDeclarationWithName: not passing any value in model

Question

For a DTD such as below, NSXMLParser does not seem to be returning anything in the model argument of foundElementDeclarationWithName. What am I missing here?

DTD -

<!DOCTYPE note [ <!ELEMENT note (to,heading)><!ELEMENT to (#PCDATA)><!ELEMENT heading (#PCDATA)>]>

NSXMLParserDelegate method -

- (void)parser:(NSXMLParser *)parser foundElementDeclarationWithName:(NSString *)elementName model:(NSString *)model 
{NSLog(@"Element - %@, Model - %@", elementName, model);}

Output -

2014-05-18 12:55:39.730 TestNSXMLParser[2146:303] Element - note Model -

2014-05-18 12:55:39.730 TestNSXMLParser[2146:303] Element - to Model -

2014-05-18 12:55:39.731 TestNSXMLParser[2146:303] Element - heading Model -

Why is no value being passed in the model argument? I would have expected the list of sub-elements, etc. found in every !ELEMENT declaration to be there.