Re: [groff] [patch] modernize -T ascii rendering of opening single quote

[Ralph Corderoy]

Hi Ingo,

> The latest US-ASCII standard, ANSI INCITS 4-1986 (R2007),
>
>   http://sliderule.mraiow.com/w/images/7/73/ASCII.pdf
>
> says on page 16;
>
>   0x60 LEFT SINGLE QUOTATION MARK, GRAVE ACCENT
>
> with this footnote:
>
>   These characters should not be used in international interchange
>   without determining that there is agreement between sender and
>   recipient (see Section B5 in Appendix B).
>
> which appears to go back to at least RFC 20 (yes, *twenty*), 1969:
>
>   http://art.tools.ietf.org/html/rfc20  (page 5)

I think you have misinterpreted the above.
The table on physical page 16 of the above US-ASCII standard says

    Graphic  Name                       Coded Representation
       '     Apostrophe, Right Single
               Quotation Mark,
               Acute Accent*            2/7
       `     Left Single
               Quotation Mark,
               Grave Accent†            6/0

    *The use of the symbols in 2/2, 2/7, 2/12, 5/14, and 7/14
     as diacritical marks is described in A5.2 in Appendix A.
    †These characters should not be used in international interchange
     without determining that there is agreement between sender and
     recipient (see Section B5 in Appendix B).

That makes clear that 27 and 60 are paired as left and right single
quotation marks.

The referenced A5.2 is

    A5.2  In order to permit the representation of languages other than
    English, two diacritical (or accent) marks have been included, and
    provision has been made for the use of four punctuation symbols
    alternatively as diacritical marks in conjunction with backspace.
    (The use of BS to form composite characters is now deprecated (see
    Section 5)).  The pairing of these punctuation symbols with their
    corresponding diacritical marks was done to facilitate the design of
    a typeface that would be acceptable for both uses.  These
    arrangements are given in Table A1. 

                          Table A1 
                Punctuation and Diacritical Marks 

        Col/  Code Table  ____________ Use _____________
        Row     Symbol      Punctuation     Diacritical

        2/2       "       QUOTATION MARK    DIAERESIS
        2/7       '       APOSTROPHE        ACUTE ACCENT
        2/12      ,       COMMA             CEDILLA
        5/14      ^       (None)            CIRCUMFLEX
        6/0       `       LEFT SINGLE
                            QUOTATION MARK  GRAVE ACCENT
        7/14      ~       (None~            TILDE

This re-states 60 is a left single quotation mark.  It also makes clear
that 27's diacritical use is as an acute accent.  A5.2 says the aim is
`a typeface that would be acceptable for both uses'.  Thus one that
makes 60 and 27 look like a left/right pair of single quotes, and also
grave and acute accents for over-striking.

RFC 20, that you cite, makes the same case but calls them opening and
closing single quotation mark instead of left and right.

> While that of course cannot retroactively change what ASCII used to
> define in the 1960ies to 1980ies, i do think an argument can be made
> that there is value in discontinuing usage of ASCII that conflicts
> with Unicode before we enter the third decade of the new millenium.

ASCII is ASCII.  Unicode may choose to change the interpretation of its
runes that overlap, but it doesn't change ASCII.

-- 
Cheers, Ralph.