説明や実例から推定し、 RFC 2822, RFC 2045, RFC 2231 などを参考に でっちあげた BNF。Message::* Perl modulesではこれを元に実装。
moe-content = moe-character *("," FWS moe-character)
/ obs-moe-content
moe-character = moe-char-name *(";" FWS moe-parameter)
/ obs-moe-character
moe-char-name = moe-value / obs-moe-char-name
moe-parameter = http-token "=" parameter-value
;; [RFC2231] extensions can be used
/ obs-moe-parameter
moe-value = value / slash-token / at-token
/ obs-moe-value
value = http-token / quoted-string
/ obs-value
parameter-value = http-token / quoted-string
/ obs-parameter-value
slash-token = value "/" value ;; belong/name
/ obs-slash-token
at-token = value FWS "@" FWS value ;; name @ belong
/ obs-at-token
obs-moe-content = [CFWS] moe-character *([CFWS] "," [CFWS] moe-character)
obs-moe-character = moe-char-name *([CFWS] ";" [CFWS] moe-char-name)
obs-moe-char-name = moe-value [CFWS]
obs-moe-parameter = token [CFWS] "=" [CFWS] parameter-value [CFWS]
/ moe-value
obs-moe-value = value *(CFWS value) [CFWS]
/ *<OCTET except ",", "*"> ;; BAD PRACTICE
obs-value = encoded-word
obs-parameter-value = token / quoted-string
obs-slash-token = value [CFWS] "/" [CFWS] value [CFWS]
obs-at-token = value [CFWS] "@" [CFWS] value [CFWS]X-Brother, X-Daughter, X-FavoriteSong, X-Husband, X-Maid, X-Me, X-Moe, X-Respect, X-Sister, X-Son, X-Sublimate, X-Wife
→あるみたいです。
示される萌えの対象は人以外にも拡大されている模様。