On a practical matter, it seems like a bad idea to have codepoints that can take up to an arbitrary number of bytes - this just screams buffer overflow problems.
So in practicality, you’re going to want an arbitrary limit on this (the article suggests as much). But if you place a limit on it then you’ve got one implementation of the standard that can decode certain characters and another that can’t. Better to have one standard that puts a hard limit on the number of bytes and another standard that uses more bytes and so on.
Technically current UTF-8 only goes up to 21 bits (that's the current UNICODE range), for the encoding itself that is an arbitrary limit though, with the 'single lead byte' method of traditional UTF-8 it could go up to 36 bits "payload".
- fully-customizable emojis (think of a RPG-like character customization screen)
- heck, why not full jpegs/gifs?
- some unicode programming script (running Doom)
- ?
That said, some very minor (HN-style) nitpick:
> Otherwise for an n byte code unit this is (5n+1) / 8n, that is 5n+1 content bits out of a total of 8n bits from n bytes. We can rewrite this as (5/8) + 1/(8n) which moderately quickly approaches 5/8 = 62.5%. It is nice that this limit is nonzero and does not depend on n.
Isn't a limit by definition no longer dependent on n?
Imagine someone using the same fully customized emoji multiple times in the same text. Seems like a waste of space. Maybe better to encode just a UUID, and send the image codebook separately.
I agree with you that Unicode urgently needs a scripting capability (*), but my plan was to just implement it using invisible tag characters [1] or something like that - but of course allowing a script to be written in a single codepoint is the much more elegant solution.
It also neatly solves the problem of how to write Unicode strings inside scripts inside Unicode strings and also scripts inside Unicode strings inside scripts inside Unicode strings.
U+E000–U+F8FF, U+F0000–U+FFFFD, and U+100000–U+10FFFD can already provide you with your own emoji, as that range has been reserved for private use. Extending the range further might make sense if you need even more space in your program, but that's a lot of space already.
2-3 bytes are not much space for anything. Sure, you could use multiple successive ones of these code points and define your own "continuation" encoding in these ranges, but that doesn't seem right to me somehow
Another one: encode instructions on how to draw the glyph into the text itself. The string becomes both the text and the font. Why not make it turing complete and as powerful/complex as TTF.
IIRC UTF-8 proposal used to go to 6 bytes as they already felt that not having part of the code point in the first byte was an issue somehow.
I think at least 7 should be allowed. 42 bits could contain all sorts of information.
"UTF-8000" is still ANSI-safe and although it loses some of the properties such as a header code only appearing once in a byte sequence, it is perfectly viable to encode arbitrarily sized unsigned integers.
UTF-8 originally supported up to six-byte encodings (see eg. RFC 2279), but it was restricted to four bytes in 2003 in order to match UTF-16 constraints :(
The number of glyphs available by adding additional bytes drops exponentially because each subsequent byte has one less bit available.
So I think if we ever were in a situation where > 1 million code points isn’t enough, then we should look at an entirely new way to serialise those code points.
I don't quite get it. 5-byte utf-8 encoding gets extra 5 bits compared to 4 byte, and 6-byte gets extra 10 bits. If you were thinking about bits in leading byte, then yes, you are losing one bit for every extra trailing byte, but you also get 6 bits from it. So adding a byte gives you extra 5 bits.
Self-synchronization in UTF-8 is intuitively a great thing to have, yet I don’t remember actively relying on it ever. Does anyone have a good example of when it‘s useful?
Another related nice property that UTF-8 has: substring search reduces to bytestring substring search. I.e. given two Unicode strings in UTF-8 encoding, you can check if one is a substring of the other by just treating them as bytestrings and checking if one bytestring is a substring of the other bytestring. This is a stronger property than self-synchronization: UTF-8 has it, but UTF-8000 doesn’t.
It's more common for programs that say they support UTF-8 to not really do so at all. It wasn't that long ago that "UTF-8" support was often just single byte, so it was little more than ASCII. Even now it's common for programs to choke on the optional BOM. Yes, it is redundant, congratulations. The spec still explicitly allows it. Three and four byte character support is still not the best, too.
> "UTF-8" support was often just single byte, so it was little more than ASCII
"Single byte UTF-8" is ASCII. That's one of its most important properties.
> Even now it's common for programs to choke on the optional BOM
And they should... BOMs (and especially the hilarious UTF-8 BOM) are strictly a legacy Microsoft/Windows thing and should be abolished along with "extended" 8-bit ASCII encodings and UCS-2/UTF-16 (only UTF-32 makes sense, but should only be used at runtime to allow random access on UNICODE code points, but not for data exchange.
It's still a joy to see how frigging elegant and extensible the UTF-8 specification is. And even without the esoteric 0xFF lead byte, the regular UTF-8 encoding with a 0xFE lead byte (11111110) would still have plenty of headroom (36 bits) compared to the current 21 bits for UNICODE.
I was about to immediately suggest UCS-X, and then pleased that the author offers a fair comparison to UCS-X and many other alternatives. Great. Too bad UCS-X is possibly more memorable name.
"your first 2 extensions (5 and 6 bytes) were clearly envisioned.
the standard (up to 4 bytes) was created to cover the size of
unicode. i thought any more description would be a waste of
paper. i think your extension from 7 to 8 bytes is a little hoaky.
i requires reading the whole string rather than "knowing" the
number of follow on bytes. so, i think the only thing new is the
7 byte version.
i appreciate the mail, but i really dont think it is useful. it is
like replacing ipv6 with ipv50."
But the nice thing about UTF-8 is that this proposal isn't really a "complication", but a minimal and natural extension of the original idea to allow more than one lead byte.
So in practicality, you’re going to want an arbitrary limit on this (the article suggests as much). But if you place a limit on it then you’ve got one implementation of the standard that can decode certain characters and another that can’t. Better to have one standard that puts a hard limit on the number of bytes and another standard that uses more bytes and so on.
Not until they decide to expand the emoji range, allocate space for all past and future fictional languages, as well as birdsong and dog barks.
Someone at the consortium is rubbing their hands with glee with all the newfound space.
But honestly, cool hack! If you invent a method to encode large numbers into bytes, why limit yourself to 24-bit numbers?
Technically current UTF-8 only goes up to 21 bits (that's the current UNICODE range), for the encoding itself that is an arbitrary limit though, with the 'single lead byte' method of traditional UTF-8 it could go up to 36 bits "payload".
- fully-customizable emojis (think of a RPG-like character customization screen)
- heck, why not full jpegs/gifs?
- some unicode programming script (running Doom)
- ?
That said, some very minor (HN-style) nitpick:
> Otherwise for an n byte code unit this is (5n+1) / 8n, that is 5n+1 content bits out of a total of 8n bits from n bytes. We can rewrite this as (5/8) + 1/(8n) which moderately quickly approaches 5/8 = 62.5%. It is nice that this limit is nonzero and does not depend on n.
Isn't a limit by definition no longer dependent on n?
I agree with you that Unicode urgently needs a scripting capability (*), but my plan was to just implement it using invisible tag characters [1] or something like that - but of course allowing a script to be written in a single codepoint is the much more elegant solution.
It also neatly solves the problem of how to write Unicode strings inside scripts inside Unicode strings and also scripts inside Unicode strings inside scripts inside Unicode strings.
(*) in RFC 04-01-2027
[1] https://en.wikipedia.org/wiki/Tags_(Unicode_block)
- Unicode-as-a-character, meaning: a whole text displayed as if it were one character, made for infinite zooming
I think at least 7 should be allowed. 42 bits could contain all sorts of information.
"UTF-8000" is still ANSI-safe and although it loses some of the properties such as a header code only appearing once in a byte sequence, it is perfectly viable to encode arbitrarily sized unsigned integers.
So I think if we ever were in a situation where > 1 million code points isn’t enough, then we should look at an entirely new way to serialise those code points.
Nobody needs more than 4.47 trillion characters. (famous last words)
Another related nice property that UTF-8 has: substring search reduces to bytestring substring search. I.e. given two Unicode strings in UTF-8 encoding, you can check if one is a substring of the other by just treating them as bytestrings and checking if one bytestring is a substring of the other bytestring. This is a stronger property than self-synchronization: UTF-8 has it, but UTF-8000 doesn’t.
It's more common for programs that say they support UTF-8 to not really do so at all. It wasn't that long ago that "UTF-8" support was often just single byte, so it was little more than ASCII. Even now it's common for programs to choke on the optional BOM. Yes, it is redundant, congratulations. The spec still explicitly allows it. Three and four byte character support is still not the best, too.
"Single byte UTF-8" is ASCII. That's one of its most important properties.
> Even now it's common for programs to choke on the optional BOM
And they should... BOMs (and especially the hilarious UTF-8 BOM) are strictly a legacy Microsoft/Windows thing and should be abolished along with "extended" 8-bit ASCII encodings and UCS-2/UTF-16 (only UTF-32 makes sense, but should only be used at runtime to allow random access on UNICODE code points, but not for data exchange.
edit: replaced false prophet site with wiki link for the original one and true timecube.com...lost to the sands of ...time.
"your first 2 extensions (5 and 6 bytes) were clearly envisioned. the standard (up to 4 bytes) was created to cover the size of unicode. i thought any more description would be a waste of paper. i think your extension from 7 to 8 bytes is a little hoaky. i requires reading the whole string rather than "knowing" the number of follow on bytes. so, i think the only thing new is the 7 byte version.
i appreciate the mail, but i really dont think it is useful. it is like replacing ipv6 with ipv50."
Some day we'll need this when we finally realise we are not alone in the universe. Alien glyphs ftw.
This is why we need the KISS enforcers.
I mean, I can derive from the text that this can encode arbitrarily large integers. So what? What's the point? I also understand that this is for fun.
https://xkcd.com/1953/