function toUnicode(domain) {
		return mapDomain(domain, function(string) {
			return regexPunycode.test(string)
				? decode(string.slice(4).toLowerCase())
				: string;
		});
	}
Converts a Punycode string representing a domain name to Unicode. Only the
Punycoded parts of the domain name will be converted, i.e. it doesn't
matter if you call it on a string that has already been converted to
Unicode.
@memberOf punycode
@param {String} domain The Punycode domain name to convert to Unicode.
@returns {String} The Unicode representation of the given Punycode
string.