Thanks Ali, I think I get close:
bool is_id(dchar c)
{
return c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= 0xc0
&& c <= 0x0d || c >= 0xd8 && c <= 0xf6 || c >= 0xf8 && c <= 0xff;
}
this doesn't include some math symbols. like c >= 0xc0 did.
