Why does C++11 allow you to declare a local variable as thread_local? [duplicate]

Question

int main()
{
    thread_local int n;
}

The code above is legal in C++11.

According to cppreference:

The thread_local keyword is only allowed for objects declared at namespace scope, objects declared at block scope, and static data members.

I just wonder:

A local variable is always on the current thread's stack, so it's always thread-local. thread_local int n; is completely identical to int n; in such contexts.

Why does C++11 allow to declare a local variable as thread_local, rather than explicitly disable it to avoid abuse?

Answer 1

According to the standard, a thread_local variable at block scope is also implicitly static. However, not all static variables are thread_local.

So

 int main()
 {
       thread_local int x;
 }

is actually equivalent to

 int main()
 {
       thread_local static int x;
 }

but different from;

 int main()
 {
       int x;    //  auto implied
 }