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There's a popular belief in Japan that a person's blood type influences their personality[0]. This probably made Japanese emoji designers add them to their pre-unicode emoji sets, which then got rolled into the first set of unicode emoji in 2010[1], along with a bunch of other Japanese symbols.

[0] https://en.wikipedia.org/wiki/Blood_type_personality_theory

[1] https://emojipedia.org/unicode-6.0/

>Sure, but why?

Some OSes display some unicode characters as emoji-default. These characters were selected for that for exactly the reason you surmise. There’s a [text presentation selector][] to enforce the text variation. This is also useful for making (yellow triangle with exclamation point inside) become (single color triangle outline with same-color exclamation point inside).

ETA: Ah, OK, here’s a post with pictures demonstrating this: https://stackoverflow.com/questions/48534667/how-to-display-...

[text presentation selector]: http://www.unicode.org/reports/tr51/#def_text_presentation_s...

> Some OSes display some unicode characters as emoji-default.

Those characters have the Emoji_Presentation Unicode property, as listed in https://www.unicode.org/Public/13.0.0/ucd/emoji/emoji-data.t...

If a site wished to exclude garish blobs from comments while permitting textual symbols, that would be the right way to do it.

The committee thinks/thought that the Fraktur letters aren’t just a different way to write letters, but symbols with a different meaning, just as ℂ, ℕ, and ℝ aren’t a different way to write C, N and R.

(And yes, they included not only 𝔸𝔹ℂ𝔻𝔼𝔽𝔾ℍ𝕀𝕁𝕂𝕃𝕄ℕ𝕆ℙℚℝ𝕊𝕋𝕌𝕍𝕎𝕏𝕐ℤ, but also 𝕒𝕓𝕔𝕕𝕖𝕗𝕘𝕙𝕚𝕛𝕜𝕝𝕞𝕟𝕠𝕡𝕢𝕣𝕤𝕥𝕦𝕧𝕨𝕩𝕪𝕫 and 𝟘𝟙𝟚𝟛𝟜𝟝𝟞𝟟𝟠𝟡 in Unicode. In iOS Safari, using the font for entering HN comments, ℂℍℙℚ renders a bit taller and bolder for me. ℝ and ℤ render taller, but not bolder. Why beats me.)

I agree with them on ℂ, ℕ, and ℝ. I also think that makes it hard to disagree with them on the Fraktur letters.

What bothers me is that for some reason only some latin letters and numbers are available as subscripts and superscripts...

Most of the Latin subscript glyphs are from the Phonetic Extensions block. They only added those that were actually used in various phonetic notations.

This Wikipedia page has a good list of why various ones were added, in addition to those from the Subscripts and Superscripts block: https://en.wikipedia.org/wiki/Unicode_subscripts_and_supersc...

> In iOS Safari, using the font for entering HN comments, ℂℍℙℚ renders a bit taller and bolder for me. ℝ and ℤ render taller, but not bolder. Why beats me.

Font fallback. HN specifies Verdana, Geneva, sans-serif. Geneva has the six characters mentioned. The rest will be rendered using a different font that covers more parts of Unicode, or that covers Unicode math specifically. With the built-in system fonts, that would be Cambria Math on Windows and one of the STIX fonts on macOS.

(Source: Firefox → Inspect Element → Fonts tab of the right Inspector pane. Chrome can do that too in a slightly different place, macOS Safari is too user-hostile to have this feature.)

I guessed that, but still can’t figure out what makes ℂℍℙℚ special. Looking again, I notice ℕ is taller, too, but not bolder. ℂℍℕℙℚℝℤ is much more “I can see why a font would have these, but not others”. That solves the issue enough for me.

(And, by the way, iOS doesn’t have Geneva, but it has a version of Verdana)

CHNPRQ and Z are the ones with actual canonical meaning:

- Complex

- Quaternion (H for Hamilton)

- Natural

- Prime

- Rational (Q for quotient)

- Real

- Zinteger

just kidding. i think Z stands for something in German.

Z for Zahlen, "numbers". "Zinteger" is an improvement, being more precise.

I have also seen

- ℙ used to denote a probability distribution

- 𝔼[X] as the expected value of a random variable X

- 𝟙_S as an indicator function for a set S (which is denoted as a subscript)

- 𝕕 as the differential and integral operator denouncing which variable to integrate over 𝕕f/𝕕x f(x) or ∫ f(x) 𝕕x

I've also seen 𝔸 for affine space, 𝔹 for the Booleans, 𝔽 for a field, 𝕂 for a field, 𝕆 for octonions and 𝕊 for surreals.

I think I've seen 𝕀 and 𝕚 for identity matrices and suchlike, and I'm sure 𝟘 also gets some use.

N are the positive integers including zero, Z are all integers.

Isn't N just the positive integers and W the one with zero?

No, the positive intergers are Z⁺ (Z^+ / Z<sup>+</sup>). N is natural numbers aka nonnegative integers aka positive integers along with (not "including", since it isn't positive) zero.

This is the math equivalent of tabs vs spaces

> The committee thinks/thought that the Fraktur letters aren’t just a different way to write letters, but symbols with a different meaning, just as ℂ, ℕ, and ℝ aren’t a different way to write C, N and R.

As to the mathematical uses, this thought is correct. Niche, obviously, but Unicode has no trouble with niche characters.

It's hard to justify the full alphabet on those lines, though.

Is it though?

There's, imo, a reasonable expectation that if some of those characters were used then some other might be later, and it's easier to have them already in the standard than reserving space for them and then having to backfill it, I suppose.

These can result in crossness amongst mathematicians: everyone uses them on the blackboard (they are called blackboard-bold after all) but half use them in printed matter and the other half insist on actual bold. Discussions on the matter lead to cold stares and the poking of fingers in the chest.

Weird that this comes up today. My Steam handle has an O and I used "negative squared Latin" characters -- I was investigating this yesterday (I found no answers!).

Last year my Steam name showed properly on MS Win10 and on Kubuntu. About 6 months ago Win 10 started showing it with the O as red. Last week the red O doesn't show at all in one part of Steam but shows white in another part.

I copied the symbols to a Unicode decoder and it showed the O name with a {blood red} modifier, something like that.

I searched briefly but couldn't find the symbol without the red colour, but it only shows red in some places: I'd pasted it into the search bar in Firefox (on Kubuntu), it showed as a number-square (1Fxxx) but then after searching it showed as the red-O character.

Utf8 is weird.

In case you enjoy the technical pedantry: UTF-8 is "just" an encoding scheme to represent the characters defined in the Unicode standard. There are other schemes in the standard (like UTF-16 or UCS-4).

Your issue here is with the characters and their representation, not with the specific encoding. Hence, what you wanted to say is: "Unicode is weird" ;)

This is the most nicely delivered pedantry I've ever read, kudos!

Here you go:

    o = "\U0001F17E"
    black = o + "\ufe0e"
    red = o + "\ufe0f"
    print(black, red)

HN seems to strip the special sequences, here it is on a pastebin instead: https://paste.debian.net/1169485/

More details: http://unicode.org/faq/vs.html http://www.unicode.org/Public/emoji/5.0/emoji-variation-sequ...

Kwpolska, most of your comments since 2011 are shadow banned. Occasionally HN readers vouch them back into visibility.

Fraktur is used in mathematics, chiefly when discussing/denoting Lie groups. I've listed some sources but you can probably Google for more.

[0] https://en.wikipedia.org/wiki/Fraktur#After_1941

[1] https://mathoverflow.net/questions/87627/fraktur-symbols-for...

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.

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.

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.

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.

¹ https://en.wikipedia.org/wiki/Letterlike_Symbols

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.

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.

𝚃𝚑𝚊𝚝'𝚜 𝚊 𝚐𝚘𝚘𝚍 𝚙𝚘𝚒𝚗𝚝. 𝚃𝚑𝚎𝚢 𝚜𝚑𝚘𝚞𝚕𝚍 𝚒𝚗𝚌𝚕𝚞𝚍𝚎 𝚝𝚑𝚘𝚜𝚎 𝚒𝚗 𝚄𝚗𝚒𝚌𝚘𝚍𝚎. 𝙾𝚑.

Welp!

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.

Still interesting.

Full-width latin characters are used to fit in the grid of Chinese/Japanese/Korean characters...they're not going anywhere.

https://en.wikipedia.org/wiki/Halfwidth_and_fullwidth_forms

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.

That style of using full width characters for emphasis might be called vaporwave, or at least related to it.

V A P O R W A V E

ＡＥＳＴＨＥＴＩＣ

https://en.m.wikipedia.org/wiki/Vaporwave

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

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.

> 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.

> The one I've stumbled across recently are the "Negative Squared Latin Capital Letter" (1F170 - 1F189 [1]). The 26 letters are there, but "A", "B", "O", and "P" are special.

In which way are they special? As far as unicode is concerned they are all the same. It's just that some have an emoji rendering variant for the blood type reasons. The rendering can be picked through representation characters: http://www.unicode.org/reports/tr51/#def_text_presentation_s...

I don't see what's special about ABOP on that page?

Interesting, every font I've seen renders them like this: https://imgur.com/a/ZPBfaK0

I thought it was suggested to render them like that from Unicode somewhere, but it's 100% possible I'm making that part up.

My recollection is for the textual characters that got repurposed as emoji, it’s implementation-defined as to whether the character defaults to text or emoji but that most renderers opt for emoji (which I believe is copying Apple’s decision here). There are variation selectors you can use to force textual or emoji presentation.

It's not implementation defined, i's defined by the Emoji_Presentation property in https://www.unicode.org/Public/13.0.0/ucd/emoji/emoji-data.t...

Some implementations are just wrong.

That file is new in Unicode 13. Also I think it might be based on Apple's behavior. I just tested every single emoji codepoint listed there, and it's almost entirely consistent with Apple's default rendering. And the very few exceptions (like ) actually seem to depend on whether the text renderer is styled or not, where it becomes emoji in styled fields (like Spotlight) and text in plain-text fields (like this comment box). This seems to only be done for the small handful of pre-existing text symbols that got turned into emoji and given the Emoji_Presentation property.

On my Android Chrome those characters are indeed not rendered specially.

Those four are listed specially as having optional emoji presentation: https://unicode.org/emoji/charts/emoji-variants.html

These all have Emoji_Presentation=No as specified in emoji-data.txt, for precisely this reason (to avoid discrepancies in rendering), but most platforms don't respect these defaults, as it's common to get strings containing emoji from mobile devices, which usually default to emoji presentation. I talk about this a little in my recent "Text layout is a loose hierarchy of segmentation" blog post.

Doesn't do anything special on desktop Firefox, but on a chromium browser A,B,O and AB have a red background while P has a green background