title: What strings are allowed in the "common name" attribute in an X.509 certificate?
body: <p>In the <em>common name</em> field of the DN of a X509 certificate, as defined in ASN.1 notation for OID "2.5.4.3", what are the allowed values?</p>
  
  <p>I know that the limit is up to 64 characters, but are all characters allowed? Digits?<br>
  E.g. are <code>.</code>s allowed? Is an IP address (x.x.x.x) a valid sequence per the ASN definition?<br>
  Is a domain name allowed?  </p>