Zero as a function name - c++

Question

The following example compiles (VS2010 C++ compiler issues a warning C4353 though) and expression (*) evaluates to 0:
#include <iostream>
#include <string>
int main()
{
0(1, "test"); // (*) - any number and type of arguments allowed
int n = 0(1, "test"); // 0
std::string str(0(1, "test")); // Debug assertion fails - 0 pointer passed
}
Is using 0 as a function name allowed/regulated by C++ standard or its resolution is compiler-specific? I was looking in the N3242 draft but could not find anything related to this. Microsoft compiler obviously resolves such construct (or one with __noop) as an integer with value 0.
warning C4353:
warning C4353: nonstandard extension used: constant 0 as function
expression. Use __noop function intrinsic instead

Answer 1

A function name is an identifier and an identifier needs to start with a non-digit (§2.11):
identifier:
identifier-nondigit
identifier identifier-nondigit
identifier digit

Answer 2

I don't know the answer, but I believe we can find it by a little googling...
Looking at the MSDN, I found two links:
C4353 : http://msdn.microsoft.com/en-us/library/2a68558f.aspx
__noop : http://msdn.microsoft.com/en-us/library/s6btaxcs.aspx
The second link explains the __noop
The __noop intrinsic specifies that a function should be ignored and the argument list be parsed but no code be generated for the arguments. It is intended for use in global debug functions that take a variable number of arguments.
Th example shows the __noop can be very interesting indeed for debug code:
#if DEBUG
#define PRINT printf_s
#else
#define PRINT __noop
#endif
int main() { PRINT("\nhello\n"); }
Another comment on the same page gives an historical hint on the 0 function:
The compiler converts the __noop intrinsic to 0 at compile time.
I guess that, once upon a time, this extension was called 0, not __noop, and that later, Microsoft created the __noop keyword because it was easier to search for, more readable, less "strange" than this 0 thing, and clearly marked as an extension (because of the two leading underscores, like MSVC's __declspec or gcc's __attribute__).
Conclusion: What about 0?
This is an extension (as per the warning message)
This is an historical, deprecated extension
Its use is deprecated in favor of __noop
It was deprecated at least at the VC++2003 time (if not before)