That's fair, but why stop there? The example that comes to mind is "Courier 12pt is the only font ever for screenplays". It's required to convey a screenplay, to my mind, like using Fraktur is required in the math space.
Despite what it may seem like, I'm really not trying to mis-parse the reasons here, I'm honestly trying to figure out where the line is, and why it's there.
> why stop there? The example that comes to mind is "Courier 12pt is the only font ever for screenplays". It's required to convey a screenplay, to my mind, like using Fraktur is required in the math space.
The screenplay is still being written in letters. Mathematical ℝ is more accurately thought of as an ideogram than a letter. If you were to write "let r be a member of ℝ", the "ℝ" would be structurally parallel to the full word "member", not to the "r" within it.
Courier for screenplays is a choice you make at the document level; blackboard bold for mathematical entities is not. ℝ is always ℝ no matter what styles apply to your document.
I really don't know, but my guess would be that in mathematics particular symbols denote particular meanings depending on the shape of / decorations on the character. Big g is different from little g which is different from bold g which is different from italic g which is different from Fraktur g. Because Fraktur g is different in meaning from just g, Fraktur gets a spot in the Unicode specs. Courier, while it is standard for screenplays, does not affect the meaning of the text of the screenplay as opposed to the use of another font.
Historically, a few were included in the Letterlike Symbols block¹ because they were present in some pre-Unicode character set. Much later it was argued that since a few were present, they all should be present.
Also note that these selective ones were part of the basic multilingual plane, where space was always a bit at a premium. They were assigned before Unicode expanded to have 17 complete 16-bit planes and space stopped being a problem.
You mix the Fraktur and Roman letters in the same mathematical manuscript, the way you mix Greek and Roman letters in the same mathematical manuscript.
Fractur is more than a font difference as it has a few ligatures (e.g. tz) that are not found in the Roman alphabet as used in modern German (ß is the only one that made the transition). And these “ligatures” aren’t really true ligatures in the sense of, say, the “fi” ligature in some fonts; they are glyphs that are close to being fully fledged letters, as, say, ö, which is an accented (umlautened) letter in Germany is a fully-fledged letter in Swedish, or how W became a freestanding letter in English.
The introduction of the Fraktur font introduces different meaning. 'R' in Fraktur would mean something different than R in another font in the same text.
I think you could argue the same for typewriter (monospace serif) fonts. Plenty of texts use them to denote the name of a variable or function in-line, much as we would use backticks to talk about `leftPad` here.
This is actually what started me down this path a while ago. I had to do a full text search feature for some text of questionable sources, and some users had taken to using the full width characters for emphasis (I think, they clearly had rules in their head for whey they'd use it, but I didn't know what the rules were). There are libraries that can handle the official Unicode normalization rules, but users don't exactly always pay attention to the official rules, so I get to start finding all sorts of weird little corners of Unicode.
Though, as I understand it, the full-width characters are there not for any modern use cases, but for historical reasons having to deal with older character sets.
I don't think there's much call for fullwidth Latin characters for that purpose. Ordinary use means typing with whatever your input method gives you. This is generally not fullwidth characters.
A clean grid would be desirable in formal use, but formal use means trying to avoid Latin characters as much as possible. It's generally possible. Plaques and the like are much more likely to say e.g. 二〇二〇年 than to say 2020年.
Grids are not just for formal use, they're useful any time you want to have aligned text, e.g. if you want to write a markdown table mixing Latin and CJK characters.
And I doubt you'd want to eliminate all formal uses of Latin characters. E.g. a plaque about a person would likely want to use their preferred name, which might be in Latin characters.
I think the full adoption of different alphabet styles as independent unicode glyphs is, overall, a conceptual mistake.
But, note that the identical process, much earlier, is how we got separate capital and lowercase forms. Writing systems never do that when they're developed.
Spacing was used for emphasis in blackletter, and consequently persisted in roman in German even after other means (e.g. italics) became common in other languages. https://de.wikipedia.org/wiki/Sperrsatz
[0] https://en.wikipedia.org/wiki/Fraktur#After_1941
[1] https://mathoverflow.net/questions/87627/fraktur-symbols-for...