!!! Overview
[{$pagename}] (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]) 

!! [RFC 5280] and [{$pagename}]
When the [subjectAltName] extension contains a [domain name|DNS Domain] system label, the domain name [MUST] be stored in the [{$pagename}] (an [IA5 String|IA5String]).

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.|Case-insensitive]  In addition, while the string " " is a legal domain name, [subjectAltName] extensions with a [{$pagename}] of " " [MUST NOT] be used.  

Finally, the use of the [DNS] representation for Internet mail addresses (subscriber.example.com instead of subscriber@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])


!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]