定义类型并在相同范围内为相同的名称使用声明

I scoured the C++11 standard (well, the n3242 draft) and the internet but could not find a precise answer. The code below compiles fine with clang 3.2 and g++ 4.7.2 as well as Visual Studio 2010, but I would expect to get an error instead.I scoured the C++11 standard (well, the n3242 d