I vaguely recall that the double-hyphen used to be disallowed in domain names, reserving them for future definition. "xn--" becoming that future definition. I'

I vaguely recall that the double-hyphen used to be disallowed in domain names, reserving them for future definition. "xn--" becoming that future definition. I'm having trouble confirming this as the double-hyphen is now very much allowed, thanks to IDN.