Missing Latin superscript lowercase letters

[Asmus Freytag]

On 3/21/2023 9:36 PM, Kent Karlsson via Unicode wrote:
> There is no law of nature (or of omputing) that says that math expressions
> must be non-plain text. Just because all of neqn/eqn, (La)TeX, MathML, 
> OMML, and indeed
> UnicodeMath are representations of math expressions that are *not* 
> plain text does not
> mean that math expressions must be expressed by a higher level 
> protocol. I.e. it could
> very well be a text level protocol (where the ”math controls” are not 
> expressed as
> printable text, but as control codes).

Using control sequences or codes for your markup does not make your 
content plain text. The fact remains that mathematical notation is 
fundamentally recursive when it comes to super/subscript: it's not 
individual letters, but entire expressions that are super/subscripted 
(and at least in theory, they cover the full range  of mathematical 
expressions) and they are recursive: they can contain nested 
super/subscripted expressions. Again, in theory, this recursion is not 
limited, except that for reasons of practicality such recursion has to 
be realized in ways that the overall expression remains legible.

Therefore, if your goal is mathematical notation, you want an operator 
that super/subscripts an expression and not code points for single 
characters. The key takeaway is the natural scoping: super/subscripting 
is applied on the level of a whole expression. That means that your 
markup needs to be scoped and that definitely makes it rich text.

The existing single characters are (almost) all encoded for use in 
phonetic notation, which is not recursive and doesn't super/subscript 
entire expressions. Instead it uses super/subscripting to indicate 
modification. Hence "modifier letters".

> Further, if some symbol/letter for some reason only ever occurred in 
> superscript
> position in math expressions, such examples would still be supporting 
> evidence for
> that symbol/letter. The closest practical example I can think of is 
> the degree sign, which
> in origin is a superscript 0.

The degree sign is either the exception that proves the rule, or 
something else: a symbol that occurs frequently in contexts that are not 
full mathematical expressions, as it is typical for unit symbols. When 
used with temperature, it's interesting to note that not all temperature 
scales use it consistently. You don't see it with Fahrenheit very often, 
for example, reflecting differences in traditional keyboard layouts.

Note that many unit symbols have one-off encodings that Unicode had to 
support via compatibility characters or even canonical duplicates (think 
micro and Ohm vs. their Greek letter counterparts). Without the need to 
support a transition from pre-existing character sets, these duplicates 
would not exist. But they do and so does the degree sign. Neither of 
them, however, form precedents for non-compatibility characters.

A./

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