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<div class="moz-cite-prefix">On 3/21/2023 9:36 PM, Kent Karlsson via
Unicode wrote:<br>
</div>
<blockquote type="cite"
cite="mid:40E26F97-2412-4BB6-8056-A628D7E5200E@bahnhof.se">
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">There is no
law of nature (or of omputing) that says that math expressions<o:p
class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">must be
non-plain text. Just because all of neqn/eqn, (La)TeX, MathML,
OMML, and indeed<o:p class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">UnicodeMath
are representations of math expressions that are *not* plain
text does not<o:p class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">mean that math
expressions must be expressed by a higher level protocol. I.e.
it could<o:p class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">very well be a
text level protocol (where the ”math controls” are not
expressed as</span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">printable
text, but as control codes).</span></div>
</blockquote>
<p>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.</p>
<p>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.</p>
<p>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".</p>
<blockquote type="cite"
cite="mid:40E26F97-2412-4BB6-8056-A628D7E5200E@bahnhof.se">
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB"> </span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">Further, if
some symbol/letter for some reason only ever occurred in
superscript<o:p class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">position in
math expressions, such examples would still be supporting
evidence for<o:p class=""></o:p></span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">that
symbol/letter. The closest practical example I can think of is
the degree sign, which</span></div>
<div style="margin: 0cm; font-size: 11pt; font-family: Calibri,
sans-serif;" class=""><span class="" lang="EN-GB">in origin </span><span
style="font-size: 11pt;" class="">is a superscript 0.</span></div>
</blockquote>
<p>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.</p>
<p>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.<br>
</p>
<p>A./<br>
</p>
<p><br>
</p>
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