On Sun, 29 Sep 2002, Devdas Bhagat wrote:
IIRC, the character set *is* restricted to [A-Za-z0-9-] for any part of a name (a FQDN will be name.name....). _ and ' ' and other pounctuation characters are not allowed in domain names.
DNS does not place these restrictions. However, the scope of DNS is way way beyond host names. Genereally, such restrictions are application (as in an application of DNS) dependent, so for host names, other characters may not be allowed, but for something else (say email addresses (yes, DNS can be used to map email addresses to mailboxes too)), they would be (yes, a space is allowed in an email address. you can also have comments in an email address. heck, you can have nested comments.).
DNS was designed so that it could be used for anything. DNS could also be used for SSL certification authorities. You'd just add a new CLASS. Current existing classes are INternet (default), CHaosnet, and HeSiod.