Well the username "~hkopy-vnhyt" would be invalid because they only allow case insensitive a-z, digits and _ underscores. I can see some reasoning, but there's

Well the username "~hkopy-vnhyt" would be invalid because they only allow case insensitive a-z, digits and _ underscores. I can see some reasoning, but there's technically nothing stopping them from allowing more universal ASCII characters at the very least.