module Mail
  grammar RFC2045

    rule tspecials
      "(" / ")" / "<" / ">" / "@" /
      "," / ";" / ":" / '\\' / "<" / ">" /
      "/" / "[" / "]" / "?" / "="
    end
    
    rule ietf_token
      "7bit" / "8bit" / "binary" /
      "quoted-printable" / "base64"
    end
    
    rule custom_x_token
      [xX] "-" token+
    end

    rule iana_token
      token+
#     <A publicly-defined extension token. Tokens
#     of this form must be registered with IANA
#     as specified in RFC 2048.>
    end
    
    rule token
      [\x21-\x27] /       # any (US-ASCII) CHAR 
      [\x2a-\x2b] /       # except SPACE, 
      [\x2c-\x2e] /       # CTLs,
      [\x30-\x39] /       # or tspecials
      [\x41-\x5a] /
      [\x5e-\x7e]
    end
    
  end
end