bug#20385: Support curved quotes in doc strings

[Ivan Shmakov]

>>>>> Eli Zaretskii <eliz@gnu.org> writes:
>>>>> From: Ivan Shmakov  Date: Thu, 14 May 2015 07:20:17 +0000

 >> The ` character is not a quotation mark at all.  In fact, it’s the
 >> spacing variant of the very same diacritical mark as is shown above
 >> e in è.

 > Any references for this?

        You mean, other than UnicodeData.txt and its derivatives?
        To quote NamesList.txt, for instance:

0060    GRAVE ACCENT
        * this is a spacing character
        x (modifier letter grave accent - 02CB)
        x (combining grave accent - 0300)
        x (reversed prime - 2035)
00B4    ACUTE ACCENT
        * this is a spacing character
        x (modifier letter prime - 02B9)
        x (modifier letter acute accent - 02CA)
        x (combining acute accent - 0301)
        x (prime - 2032)
        # 0020 0301
0300    COMBINING GRAVE ACCENT
        = Greek varia
        x (grave accent - 0060)
        x (modifier letter grave accent - 02CB)
0301    COMBINING ACUTE ACCENT
        = stress mark
        = Greek oxia, tonos
        x (apostrophe - 0027)
        x (acute accent - 00B4)
        x (modifier letter prime - 02B9)
        x (modifier letter acute accent - 02CA)
        x (greek tonos - 0384)

        I presume that if U+0060 was /not/ be meant to be a spacing
        grave accent – there would be some other code point for that
        purpose, just like there /is/ such a code point (U+00B4) for a
        spacing /acute/ accent.

        Given that standards are intended to document existing practice,
        I’d expect Unicode to note that ‘`’ may be used as a quotation
        mark in legacy applications.  I’d be surprised to find it
        /recommending/ such use, though.

        Also, while I have no copy of USAS X3.4-1968 at hand, RFC 20
        (which, AIUI, was intended to be a copy of it itself) has the
        following note:

   6/0         `           Grave Accent [2, 3] (Opening Single Quotation
                                   Mark)

[…]

      2 The use of the symbols in 2/2, 2/7, 2/12, 5/14, /6/0, and 7/14
   as diacritical marks is described in Appendix A, A5.2

        Alas, the appendices are not included in RFC 20.  Still, ECMA-6
        (which also names 6/0 GRAVE ACCENT) reads:

    B.2.3

    Composite graphic characters and repertoire

    ECMA-6 permits the construction of composite graphic characters by
    using the control characters BACKSPACE and CARRIAGE RETURN to image
    two or more graphic characters at the same character position.

-- 
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