[ietf-dkim] plain-text and g=

[Tony Hansen]

I misspoke in the meeting about there being no ABNF for plain-text. It
turns out that there is no use of the term plain-text in any ABNF
production. So there does not need to be an ABNF for plain-text.

However, the term "plain text" is not defined anywhere.

Furthermore, the tags that *are* marked as requiring plain text all use
productions that do not permit utf8.

For example, g= is defined in terms of dot-atom:

   key-g-tag       = %x67 [FWS] "=" [FWS] key-g-tag-lpart
   key-g-tag-lpart = [dot-atom] ["*"] [dot-atom]

which is taken from 2822 and is defined to include only the following:

dot-atom        =       [CFWS] dot-atom-text [CFWS]

dot-atom-text   =       1*atext *("." 1*atext)

atom            =       [CFWS] 1*atext [CFWS]

atext           =       ALPHA / DIGIT /
	"!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" /	"-" / "/" /
	"=" / "?" / "^" / "_" / "`" / "{" / "|" / "}" / "~"

If we want to extend g= to permit utf8, or any other tag values, we'll
need to do that explicitly and choose a different set of ABNF leaf tokens.

	Tony Hansen
	tony at att.com