Re: operator | for an enum?

I wonder if I'm breaking any rules here?

Consider

enum MYTYPE { ZERO=0, ONE, TWO, THREE, FOUR, FIVE, SIX, SEVEN };

The names have been changed to protect the innocent, but I like
enums like this as the names are shown in the debugger, and if they
are meaningful it means I don't have to grope around in the
recesses of my memory to find what 6 represents.

But one thing which doesn't automatically work is

MYTYPE a=ONE; b=TWO;
MYTYPE c = a|b;

But it appears to be fine if I include in my header file

inline MYTYPE operator | (MYTYPE a, MYTYPE b )
{
   return (MYTYPE)( ((UINT)a) | ((UINT)b) );
}

Is it legal to define such operators on enums? - So far I haven't
found it in the language spec anywhere but it seems to compile fine.

And while we're at it, is the following syntax ok?

inline MYTYPE operator |= (MYTYPE a, MYTYPE b )
{
  a = (MYTYPE)( ((UINT)a) | ((UINT)b) );
   return a;
}

[I usually do such things with class members, but obviously that's
not appropriate here, and I'm blowed if I can remember the syntax
(or indeed find it).]