Superscript and Subscript Characters in General Use

[Marcel Schneider]

On Wed, 4 Jan 2017 00:36:38 -0500, John W Kennedy wrote to Asmus Freytag:

> As long as this is being discussed, what about the historic practice of using 
> M‘ (nowadays often seen as M’ instead) in Scottish names—e.g., M‘Donald—as a 
> typographic substitute for M(superscript c)? 

My first idea at reading was, that this adds to the examples of character re-use 
from lack of appropriate characters on the keyboard (or in the typecase, as you 
explained later).

On Tue, 3 Jan 2017 22:48:09 -0800, Asmus Freytag (c) replied:

> What about it? There are dozens, perhaps hundreds of fallbacks that have
> been used over time, both in hot metal typography as well as with
> typewriters or digital systems. Some practices may have started in ways
> similar to a fallback, but have now evolved into standard practice.
> Other ones remain fallbacks or went out of fashion.
> 
> It's an interesting example, but what kind of discussion did you have in
> mind? 

This designs the principle of user choices that may supersede standard preferences. 
So Iʼm picking up that the accurate concept is FALLBACK. It probably expands to 
the rule that every character may be re-used as a fallback for any other character 
(unformatted or formatted) if this meets user expectations and preferences. 

Consequently, the entire ranges of modifier letters, punctuation, symbols and other 
characters can be used as fallbacks to write superscript abbreviations. Some of 
them are obviously more appropriate than others: MODIFIER LETTER SMALL C would 
better fit this use case but was unavailable somewhere (typecase, charset, keyboard) 
and thus was not retained, while the second-best (single open-quote, or MODIFIER 
LETTER TURNED COMMA, as Denis Jacquerye suggests) was used.

So we have the confirmation that itʼs up to the users and their keyboard layout 
providers and font designers to choose the best fitting fallbacks among the 
existing Unicode characters. For lack of anything better, MODIFIER LETTER SMALL E 
is the designated fallback candidate for the hypothetical/on-coming/up-coming 
French ordinal indicator _kind-of-'ᵉ'_, and the other three ordinal indicator 
fallbacks 'ʳ', 'ˢ' and 'ᵈ' are also readily available. 

Citing again another example: To represent the French abbreviation of ‘number’, 
MODIFIER LETTER SMALL O would better fit than the widely used DEGREE SIGN, that 
is the only one available on the current keyboard among these two, while the 
RING ABOVE would be too small, MASCULINE ORDINAL INDICATOR (sometimes used as 
another fallback by people who have it on the keyboard) has often an underline 
that is unpreferred in French, and SUPERSCRIPT ZERO is somewhat too big:
                 nᵒ - n° - n˚ - nº - n⁰

The fallback scheme applies to custom vulgar fractions as well: their representation 
with super-/subscript digits has seemingly the status of a fallback, during the time 
when itʼs not yet recognized as alternate standard representation. I mean that 
officially, it is likely to be considered a fallback, while in practice, it has 
already become a working solution.

Further, on Wed, 4 Jan 2017 22:12:00 +0000, Richard Wordingham wrote:
> 
> > 2017-01-04 12:44 GMT+01:00 John W Kennedy :
> >
> > > No it isn’t. It isn’t an apostrophe; it’s a left single quote,
> > > although some modern printers mistakenly suppose it to be an
> > > apostrophe, and substitute one. And it isn’t an elision; it’s meant
> > > as a substitute glyph for a superscript c.
> 
> For which I would suggest U+02BF MODIFIER LETTER LEFT HALF RING would
> be the best modern representative of the substitute character!

While Iʼd thought a wile about the left half ring (having it on the keyboard, in 
group 3), when trying it I found it too tiny: MʿDonald - M‘Donald. 
Why a representative of a substitute? Probably because MODIFIER LETTER SMALL C is 
already used as a substitute of superscript small C, despite of the Standard 
specifying that the modifier letters are not [intended as] a substitute for this. 
So the left half ring might be considered the best representative, while the best 
modern *solution* for a substitute would really be the modifier letter:
               MᶜDonald - M‘Donald ( - MʿDonald).

> 
> Of course, that would further increase confusion of those who initially
> read U+02BF as a superscript 'c', and only later, if ever, realise that
> it's actually a rough breathing carefully distinguished from the
> similar punctuation marks. 

Indeed it would be a pity to stick with alternatives and worst case fallbacks 
if a better solution is readily available. Among MODIFIER LETTERs, TURNED COMMA 
is already a “typographical alternative for” REVERSED COMMA and LEFT HALF RING, 
so that it could seem consistent that SMALL C be a typographical alternative for 
superscript small c, knowing that the (probably) only thing that matters of 
a fallback, is whether it evolves into standard practice, remains a fallback, 
or goes out of fashion. E.g., the DEGREE SIGN had evolved into standard practice 
as a (representative of the) substitute for superscript small o, but could perhaps 
go out of fashion when a comprehensive set of MODIFIER SMALL letters can be easily 
accessed on standard keyboards, in the best case completed with automatic sequences 
for 'nᵒ' and 'Nᵒ', that have the advantage over the degree sign that they can easily 
be complemented with a plural s: 'nᵒˢ' and 'Nᵒˢ'.

Marcel