这个C++技术是如何将类型添加到一个被调用的类中的?

我刚刚找到了一些C++代码 http://msdn.microsoft.com/en-us/library/k8336763(VS.71).aspx ,它使用了我以前从未见过的技术向现有类添加类型:

class Testpm {
public:
   void m_func1() { cout << "m_func1\n"; }
   int m_num;
};

// Define derived types pmfn and pmd.
// These types are pointers to members m_func1() and m_num, respectively.
void (Testpm::*pmfn)() = &Testpm::m_func1;
int Testpm::*pmd = &Testpm::m_num;

int main() {
   Testpm ATestpm;
   Testpm *pTestpm = new Testpm;

   // Access the member function
   (ATestpm.*pmfn)();
   (pTestpm->*pmfn)();   // Parentheses required since * binds

   // Access the member data
   ATestpm.*pmd = 1;
   pTestpm->*pmd = 2;

   cout  << ATestpm.*pmd << endl
         << pTestpm->*pmd << endl;
}

有人能告诉我这个定义派生类型的技术叫什么,或者让我看一些关于它的文档吗?我在使用C++的13年中从未遇到过这样的问题,希望结束我的无知。