c# - XPathNavigator.Evaluate 返回不正确的值？

Question

我期待这段代码返回true，但它没有？我在这里想念什么。

 string xml = @"<!DOCTYPE root [ <!ELEMENT e (e*) ><!ATTLIST e  id    ID    #REQUIRED>]>
         <data><e id=""NUM_CPUS"">2</e><e id=""ACE_PRESENT"">1</e></data>";
  XPathDocument doc = new XPathDocument(new StringReader(xml));
  string expr = "(id('NUM_CPUS'))>=1 and (id('ACE_PRESENT'))=1";
  XPathNavigator nav = doc.CreateNavigator();

  XPathExpression query = nav.Compile(expr);

  object result = nav.Evaluate(query);
  bool b = bool.Parse(result.ToString());

  if (!b)
    throw new Exception("Should be true");

Answer 1

添加标题，使这项工作：

<!DOCTYPE root [ <!ELEMENT e (e*) ><!ATTLIST e  id    ID    #REQUIRED>]>