Overview#DNSName (really dNSName) is an Abbreviation for Hostname as used in several RFCs (RFC 5280) as the Hostname as it exists within the Domain Name System (DNS) subjectAltName extension contains a domain name system label, the domain name MUST be stored in the DNSName (an IA5 String).
The name MUST be in the "preferred name syntax", as specified by Section 3.5 of RFC 1034 and as modified by Section 2.1 of RFC 1123. Note that while uppercase and lowercase letters are allowed in domain names, no significance is attached to the case. In addition, while the string " " is a legal domain name, subjectAltName extensions with a DNSName of " " MUST NOT be used. Finally, the use of the DNS representation for Internet mail addresses (subscriber.example.com instead of email@example.com) MUST NOT be used; such identities are to be encoded as rfc822Name. Rules for encoding internationalized domain names are specified in Section 7.2. (RFC 5280)