Is º an unicode alphabetic character?

[AsmMan via Digitalmars-d-learn]

what's an unicode alphabetic character? I misunderstood 
isAlpha(), I used to think it's to validate letters like a, b, è, 
é .. z etc but isAlpha('º') from std.uni module return true. How 
can I validate only the letters of an unicode alphabet in D or 
should I write one?

I know I can do:
bool is_id(dchar c)
{
        return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'z' || c >= 0xc0;
}

but I'm looking for a native, if any