[ietf-dkim] dots in selectors

[Eric Allman]

In an attempt to clarify selectors and their interaction with DNS, 
I've made the following changes to the draft:

Section 3.1, paragraph 3 now reads:

        Periods are allowed in selectors and are component
        separators. If keys are stored in DNS, the period defines DNS
        label boundaries in a manner similar to the conventional use
        in domain names. Selector components might be used to combine
        dates with locations; for example, "march2005.reykjavik". In
        a DNS implementation, this can be used to allow delegation of
        a portion of the selector name-space.

The ABNF following that paragraph also says:

        selector =   sub-domain *( "." sub-domain )

(this is unchanged).  The sub-domain non-terminal is defined in RFC 
2821:

      sub-domain = Let-dig [Ldh-str]
      Let-dig = ALPHA / DIGIT
      Ldh-str = *( ALPHA / DIGIT / "-" ) Let-dig

I hope this makes it clear that dots are not permitted as part of a 
DNS label that is representing a component of a selector.  If not, 
please suggest improved language.

eric