Unicode Normalization Forms: When ö ≠ ö
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blog.opencore.ch
Years ago I read a rant by someone who insisted that being able to mix arbitrary languages into a single String object makes sense for linguists but for most of us we would be better off being able to a assert that a piece of text was German, or sanskrit, not a jumble of both. It's been living rent free in my head for almost two decades and I can't agree with it, nor can I laugh it off.
It might have been better if the 'code pages' idea was refined instead of eliminated (that is, the string uses one or more code pages, not the process). I don't know what the right answer is, but I know Every X is a Y almost always gets us into trouble.
That's simple - it is provably wrong. While relatively uncommon there are plenty of examples that would contradict this statement. And it's not about being able to encode the Rosetta Stone - non-scientists mix languages all the time, from Carmina Burana to Blinkenlights. They even make meaningful portmanteau words and write them with characters from multiple unrelated writing systems, like "заshitано" (see - Latin and Cyrillic scripts in the same single word!)
The word is a joke and there is no well-defined meaning. I've seen it used as both "it counts but it's shitty" and as a way to give credit for a failure.
Surely that's not the best example, but it's a word I've remembered.
For languages that have Latin-derived writing systems, it's not uncommon to use English letters (without diacritics) to write the language -- how would that be handled? In addition, thanks to Han unification (though this would've been a problem anyway -- loads of characters would've been unified anyway) all similar CJK Hanzi/Kanji/漢字 characters are mapped to the same codepoint regardless of language. This means that for some sentences it is entirely possible for you to not know whether a sentence fragment is Chinese or Japanese without more context and a native-like understanding of the language.
Also in many languages English words are written verbatim meaning that you can have sentences like (my Japanese is not perfect, this is just an example):
> あの芸人のYouTube動画を見たの？面白すぎるww
And (at least in Japanese) there are loads of other usage of Latin characters aside from loan words that would be too unwieldy to write in katakana -- "w" is like "lol", and fair few acronyms (BGM = Background Music, CM = Advertisement, TKG = 卵かけご飯 = (Raw) Egg on Rice). There are other languages that have similar "issues", but unfortunately I can't give any more examples because the only other language I speak (Serbian) writes everything (even people's names) phonetically.
As an aside -- if anyone ever has to support CJK languages (in subtitles for instance), please make sure you use the right fonts. While Unicode has encoded Han characters with the same codepoint, in different languages the characters are often drawn differently and you need to use the right font for the corresponding language (and area -- Mandarin speakers in different areas write some characters differently -- 返 is different in every CJK locale). Many media players and websites do not handle this correctly and it is fairly frustrating -- the net result is that Japanese is often displayed using Chinese fonts which makes it uncomfortable to read (it's still obvious what the character is, it's just off-putting).
I've made so many horrible localization errors in the past because I had to translate things into 30 different languages and I can only barely read a handful of them, so I just copy and paste whatever the translators give me.
Incidently, I saw Japanese text recently that was quoting both English AND Arabic in the same sentence. And this was in a block of vertical text. That is literally a worst-case scenario I think. You have RTL-vertical text also containing RTL- and LTR-horizontal text. And unlike English, which when placed into vertical Japanese text, you can essentially choose whether you want the characters going vertically or sideways - you can't do that with Arabic as the letters must be joined together, I don't believe you can break them down and stack them on top of each other.
Why can't we all just convert to Esperanto? ;)
Look up Mongolian script and you might change your mind :)
From Wikipedia: "Computer operating systems have been slow to adopt support for the Mongolian script, and almost all have incomplete support or other text rendering difficulties."
On *nix systems, I ran this through the base64 command; the data was UTF8, which meant that in practice it was ASCII (because we didn't have any special characters in our commit messages).
On Windows systems... oh god. The system treats all text as UTF-16 with whatever byte order, and it took me ages to figure out how to get it to convert the data to UTF-8 before encoding it. Eventually it started working, and it worked for a while until it didn't for whatever reason. I ended up tearing out all the code and just encoding the UTF-16 in base64 and then processing that into UTF-8 on the master where I had access to much saner tools.
Generally speaking, "Unicode" works great in most cases, but when you're dealing with systems with weird or unusual encoding habits, like Windows using UTF-16 or MySQL's "utf8" being limited to three bytes per unicode character instead of four, everything goes out the window and it's the wild west all over again.
The utf-16 fact about Windows was apparently unknown to my predecessor.
Who wrote some nasty c-language binary to copy the data, knock the upper byte off of each character ahead, and save the now ASCII text to a new file of the mysql load.
The encoding='utf-16' argument was all that was needed.
For want of a nail. . .
The "maybe strip null bytes" code lived for years "just in case" after I fixed that because people couldn't believe that's all that was ever "wrong" with the data.
Mostly because of weird interactions of different libraries, languages and operating systems.
This isn't true, for starters it's two encodings UTF-16LE and UTF-16BE.
Thing is, people who are not linguists do want to mix languages. It's very common in some cultures to intersperse the native language with English. But even if not, if the language in question uses a non-Latin alphabet, there are often bits and pieces of data that have to be written down in Latin. So that "most of us" perspective is really "most of us in US and Western Europe", at best.
For domains and such, what I think is really needed is a new definition of string equality that boils down to "are people likely to consider these two the same?". So that would e.g. treat similarly-shaped Latin/Greek/Cyrillic letters the same.
But you also have "Script" (for ö "Latin). Some characters belong to more than one script though. Unicode will tell you that.
Unicode also has a variety of algorithms available already written. One of the most relevant ones here is... normalization. To compare two strings in the broadest semantic sense of "are people likely to consider these the same", you want want a "compatibility" normalization. NFKC or NFKD. They will for instance make `1` and `¹`[superscript] the same, which is definitely one kind of "consider these the same" -- very useful for, say, a search index.
That won't be iron-clad, but that will be better than trying to role your own algorithm involving looking at character metadata yourself! But it won't get you past intentional attacks using "look-alike" characters that are actually different semantically but look similar/indistinguishable depending on font. The trick is "consider these the same" really, it turns out, depends on context and purpose, it's not always the same.
Unicode also has a variety of useful guides as part of the standard, including the guide to normalization https://unicode.org/reports/tr15/ and some guides related to security (such as https://unicode.org/reports/tr36/ and http://unicode.org/reports/tr39/), all of which are relevant to this concern, and suggest approaches and algorithms.
Unicode has a LOT of very clever stuff in it to handle the inherently complicated problem of dealing with the entire universe of global languages that Unicode makes possible. It pays to spend some time with em.
I recommend the Moderate Restrictive Security profile for identifiers for mixed scripts. TR39. Plus allow Greek with Latin. This way you can identify Cyrillic, Greek, CFK or any recommended script, but are not allowed to mix Cyrillic with Greek. And you still can write math with Greek Symbols.
What we don't have are a standard string library to compare or find strings. wcscmp does not do normalization. There is no wcsfc (foldcase) for case insensitivity. There's no wcsnorm or wcsnfc. I'm maintaining such a library.
coreutils, diff, grep, patch, sed and friends all cannot find Unicode strings, they have no string support. They can only mimic filesystems, finding binary garbage. Strings are so rthi g different than pure ASCII or BINARY garbage. Strings have an encoding and are Unicode.
Filesystems are even worse because they need to treat filenames as identifiers, but do not. Nobody cares about TR31, TR39, TR36 and so on.
Here is an overview of the sad state of Unicode unsafeties in programming languages: https://github.com/rurban/libu8ident/blob/master/c11.md
One of the problems is, how do you distinguish symbols and words? A simple way to do this is to classify something as a symbol if it is just a single character, and as a word otherwise. For example, "α-β" would consist of two symbols, separated by a hyphen, but "αβ" is a word and normalised to "av" based on some convention on how to "latinise" greek words.
In English, jalapeño is correctly spelled with or without the eñe (and AFAIK the letter doesn't have a name in English, you have to use the Spanish name). So, there's an English word that doesn't use the letters assigned to the English alphabet. How do we place the word? Well, obviously English borrowed the word from Spanish, so it's a Spanish word. Well, no, it's only the Spanish adjectivization of Nahautl words used to name the place called Xalapa...
It's hard enough to know what a letter is in unicode. Breaking things into words is just another massive headache.
Presumably the person who wrote it speaks a single language.
Just because something is not useful to them, it doesn't mean it is not useful in general. There are millions of polyglots as well as documents that include words and names in multiple scripts.
Of course you'd always need an "unrestricted" string (to speak to the rest of the system if necessary), but there are very few natural strings out there in the world that consist of half-a-dozen languages just mishmashed together. Those exceptions can be treated as exceptions.
> there are very few natural strings out there in the world that consist of half-a-dozen languages just mishmashed together
...in your experience. What is an almost-absurd exception to you, is every day life to others.
Presumably the person who wrote it speaks English.
If a programming language allows text processing but can't even properly compare unicode text, it is buggy and needs to be fixed. If an operating system can't deal with unicode, it's buggy and needs to be fixed.
I'm not exactly sure how a code page is supposed to help us here. Developers have trouble supporting multiple languages when they're all in the Unicode Standard. Supporting code pages for languages they've never heard of? Not a chance.
In Unicode spec terms, 'UTS 39 (Security)' contains the description of how to do this, mostly in section 5, and it relies on 'UTX 24 (Scripts)'.
It's more nuanced than your example but only slightly. If you replace "German" with "Japanese" you're talking about multiple scripts in the same 'writing system', but the spec provides files with the lists of 'sets of scripts' each character belongs to.
The way that the spec tells us to ensure that the word 'microsoft' isn't made up of fishy characters is that we just keep the intersection of each character's augmented script sets. If at the end, that intersection is empty, that's often fishy -- ie, there's no intersection between '{Latin}, {Cyrillic}'.
However, the spec allows the legit uses of writing systems that use more than one script; the lookup procedure outlined in the spec could give script sets like '{Jpan, Kore, Hani, Hanb}, {Jpan, Kana}' for two characters, and that intersection isn't empty; it'd give us the answer "Okay, this word is contained within the Japanese writing system".
In any case, there are emoji which are expected to be a part of text.
On one hand, it would be great to separate areas of different encodings inside a string. But character codes are already such separators.
Two things need to go though: the assumption of linear-time index-based access to characters in a string, and the custom to compare strings as byte arrays.
The first us already gone from several advanced string implementations. The second is harder: e.g. Linux filesystems support Unicode by being encoding-agnostic and handling names as byte sequences. Reworking that would be hard if practical at all.
I think more generally, the idea that a langauge std lib can provide string equality for human langauge strings is just silly. String equality is an extremely context dependent, fuzzy operation, and should be handled by each context differently. For example for Unicode hostname to certificate mapping, hostname equality should be handled by rendering the hostname in several common web fonts and checking if the resulting bitmaps are similar. If they are, then assigning different certificates to these equal hostanmes should not be done.
Of course, in other contexts, there are different rules. For example, if looking up song names, the strings "jalapeno" and "jalapeño" should be considered equal, in English text at least.
Unless I missed something that is impossible with Unicode. Mixing multiple languages would require a way to specify the language used for case conversion, sorting and font rendering settings mid string and I don't think that Unicode has that. For example try to write a program that correctly uppercase a single string containing both an English i and a Turkish i in your favorite Unicode supporting language, the code point is the same for both, and you generally only get to specify one language globally or per function call.
Obviously yes, it would have been better.
But Unicode was designed by the same people who designed ASCII - monolingual Americans who never had to deal on a daily basis with anything that doesn't fit into the 26 letters of the English alphabet. So here we are.
This is not even remotely true.
Also, do you remember what (polyglot computing) life was like before Unicode?
These are all myths, and APIs for such things are bugs. The only thing you can meaningfully do with two pieces of arbitrary Unicode text is to say if they are byte-by-byte equal. For any other operation, you need to have specific business logic.
For example, are "Ionuț" and "Ionut" and "Ionutz" the same string or different strings? There is no generic answer: depending on the intended business logic, they may be identical or not (e.g. if we consider these to be Romanian names, they should be considered identical for search purposes, but probably not identical for storage purposes, where you want to remember exactly how the person spelled their name).
A related problem is that most langauges have no separate types for Text/String on one hand, and Symbol on the other. Text or other Strings should be opaque human text, that can only be interpreted by specific code, offering almost no API (only code point iteration). Symbols should be a restricted subset of Unicode that can offer fuller features, such as lengths, equality, separation into words etc. This would be the type of JSON key names used in serialization and deserialization, for example.
In fact what Unicode has end up with is so horrible, it's a major exercise in coding just to answer a simple question like "is there an 'o' in this sentence", as in Python3's "'o' in sentence" does not always return the right result.
Unicode's starting point was all wrong. There is an encoding that did a perfectly good job of mapping graphemes to numbers: ISO-10646. In fact Unicode is based on it, by then committed their original sin: they decided all the proposed ISO-10646 encodings (ie, how the numbers are encoding into byte streams) were crap, so they released a standard that combined two concepts that should have remained orthogonal: codepoints and encoding those codepoints to a binary stream.
Now it's true ISO-10646 proposed encodings were undercooked. That became painfully apparent when Ken Thompson came up with utf-8. But no biggie right: utf-8 was just another ISO-10646 encoding, just let it take over naturally. The Unicode solution to the encoding problem was to first decide we would never need more than 2^16 codepoints, then wrap it up in "one true encoding everyone can use": UCS2. Windows and Java, among others, bought the concept, and have paid the price ever since.
They were wrong of course. 2^16 was not enough. So they replaced the USC2 encoding with UTF-16 which was sort of backwards compatible. But not one UTF-16, oh no, that would be too simple. We got UFT-16LE and UTF-16BE. Notice what has happened here: take identical pieces of text, encode them as valid Unicode, and end up with two binary objects that were different. Way to go boys!
But that wasn't the worst of it: they managed to screw up UTF-16 so badly it didn't expand the code space to the 2^32 points, just 2^20. And in case you can't guess what happens next, I tell you: turns out there are more than 2^20 grapheme's out there.
What to do? Well there are a lot of characters that are "minor variants” of each other, like, like o and ö. Now Unicode already had a single code point for ö but to make it all fit and be uniform they decided "Combining Diaeresis” was the way these things should be done in future. So now the correct way to represent ö is a code point that says "add an umlaut to the next character (provided it isn't another diaeresis)" followed by the code point for o. But as the original codepoint for ö still exists, we can have two identical graphemes that don't compare as equal under Unicode, which is how we get to ö ≠ ö.
So it's not only Python3 "'o' in sentence" that doesn't always always work. We arrived at the point that "'ö' in sentence" can't be done without some heavy lifting that must be done by a library. Just to make it plain: some CPU's can do "'o' in sentence" in a single instruction. That simple design decison have lost is orders of magnitude in CPU efficiency.
I know these are strong words, but IMO this is a brain dead, monumental fuckup, making things acre feet, furlong fortnights look positively sane. It's time to abandon Unicode, and it's “Combining Diaeresis” in particular and go back to basics: ISO-10646 and utf-8. UTF-8 provides a 28 bit encoding space, which is more than enough to realise the one the single guiding principle that ISO-10646 was founded on: one codepoint per grapheme.
It won’t happen of course, so as a programmer I’ll have to deal with the shit sandwich the Unicode consortium has served up for the rest of my life.
And, many of the examples I gave earlier will not go away. The problem of similar URLs using different characters would be smaller, but not gone - microsoft.com and mícrosoft.com still look too similar. Text search should still support alternate spellings (color and colour). People's names would still have multiple legally identical spellings.
This could occur on systems that normalise to NFC as well: NFC lengthens some strings, e.g. 𝅗𝅥 (U+1D15E MUSICAL SYMBOL HALF NOTE) normalises to 𝅗𝅥 (U+1D157 MUSICAL SYMBOL VOID NOTEHEAD, U+1D165 MUSICAL SYMBOL COMBINING STEM) in both NFC and NFD (similar happens in various Indic scripts, pointed Hebrew, and the isolated case of U+2ADC FORKING which is special for reasons UAX #15 explains), but I don’t think there are any file systems that actually normalise to NFC? (APFS prefers NFC, but doesn’t normalise at the file system level.)
The remaining concern would be that NFC could take more UTF-8 code units than NFD despite adding a character, but in practice this doesn’t occur (checked on NormalizationTest-3.2.0.txt).
I thought the generally recommended way to deal with file names is to treat as a block of bytes (to the extent that e.g. rust has an entirely separate string type for OS provided strings), or just to allow direct encoding/decoding but not normalisation or alteration.
Or you could have one file `göteborg.txt`, and when you try to ask for it as `göteborg.txt`, the system tells you "no file by that name".
Unicode normalization is the solution to this. And the unicode normalization algorithms are pretty good. The bug in this case is that the system did not apply unicode normalization consistently. It required a non-default config option to be turned on to do so? I don't really understand what's going on here, but it sounds like a bug in the system to me that this would be a non-default config option.
Dealing with the entire universe of human language is inherently complicated. But unicode gives us some actually pretty marvelous tools for doing it consistently and reasonably. But you still have to use them, and use them right, and with all software bugs are possible.
But I don't think you get fewer crazy edge cases by not normalizing at all. (In some cases you can even get security concerns, think about usernames and the risk of `jöhn` and `jöhn` being two different users...). I know that this is the choice some traditional/legacy OSs/file systems make, in order to keep pre-unicode-hegemony backwards compat. It has problems as well. I think the right choice for any greenfield possibilities is consistent unicode normalization, so `göteborg.txt` and `göteborg.txt` can't be two different files with two different filenames.
[btw I tried to actually use the two common different forms of ö in this text; I don't believe HN normalizes them so they should remain.]
Unless it was meant to be for performance?
Linux filenames are a sequence of non-zero bytes (they might be ASCII, or at least UTF-8, they might be an old 8-bit charset, but they also might just be arbitrary non-zero bytes) and Windows file names are a sequence of non-zero 16-bit unsigned integers, which you could think of as UTF-16 code units but they don't promise to encode UTF-16.
Probably the files have human readable names, but, maybe not. If you're accepting command line file names it's not crazy to insist on human readable (thus, Unicode) names, but if you process arbitrary input files you didn't create, particularly files you just found by looking around on disks unsupervised - you need to accept that utter gibberish is inevitable sooner or later and you must cope with that successfully.
Rust's OSStr variants match this reality.
A) The programmer is a almighty god who knows everything, we just expose him to the raw thing
B) The programmer is a immature toddler who cannot be trusted, so we handle things for them
One example is when you submit a file in Safari it doesn't normalize the file name while js file.name does.
As for APFS, it ~~doesn’t~~didn’t normalize but I believe it still requires UTF-8. And the OS will normalize filenames at a higher level. EDIT: they added native normalization. At least for iOS, I didn’t dig enough to check it macOS is doing native normalizing or is just normalization-insensitive.
(On the use of version 3.1, note that in practice version 3.2 is used, correcting one typo: see <https://www.unicode.org/versions/corrigendum3.html>.)
I find a few references to it being slightly different, but not one of them actually says what’s different; Wikipedia is the only one with a citation (<https://en.wikipedia.org/wiki/HFS_Plus>: “and normalized to a form very nearly the same as Unicode Normalization Form D (NFD)[12]”), and that citation says it’s UAX #15 NFD, no deviations. One library that handles HFS+ differently switches to UCD 3.2.0 for HFS+ <https://github.com/ksze/filename-sanitizer/blob/e990e963dc5b...>, but my impression from UAX #15 is that this should be superfluous, not actually changing anything. (Why is UCD 3.2.0 still around there? Probably because IDNA 2003 needs it: <https://bugs.python.org/issue42157#msg379674>.)
Update: https://developer.apple.com/library/archive/technotes/tn/tn1... has actual technical information, but the table in question doesn’t show Unicode version changes like they claim it does, so I dunno. Looks like maybe from macOS 10.3 it’s exactly UAX #15, but 8.1–10.2 was a precursor? I’m fuzzy on where the normalisation actually happens, anyway.
# FIXME: improve HFS+ handling, because it does not use the standard NFD. It's
# close, but it's not exactly the same thing.
'hfs+': (255, 'characters', 'utf-16', 'NFD'),
> The characters with codes in the range u+2000 through u+2FFF are punctuation, symbols, dingbats, arrows, box drawing, etc. The u+24xx block, for example, has single characters for things like "(a)". The characters in this range are not fully decomposed; they are left unchanged in HFS Plus strings. This allows strings in Mac OS encodings to be converted to Unicode and back without loss of information. This is not unnatural since a user would not necessarily expect a dingbat "(a)" to be equivalent to the three character sequence "(", "a", ")" in a file name.
> The characters in the range u+F900 through u+FAFF are CJK compatibility ideographs, and are not decomposed in HFS Plus strings.
The bit about the u+24xx block is misleading, the decomposition of the characters I looked at there (such as ⒜) are compatibility canonicalizations. However the CJK compatibility ideographs is a working example. U+F902 (車) decomposes to U+8ECA (車) regardless of normalization form but the technote says these must not be decomposed.
$ echo test > $'\xc3\xb6'
$ cat $'\x6f\xcc\x88'
cat: ö: No such file or directory
$ zfs create -o normalization=formD pool/dataset
$ echo test > $'\xc3\xb6'
$ cat $'\x6f\xcc\x88'
testAnd then brought it back. It normalizes now.
> Wrappers around it like whatever Nextcloud is doing should be treating the filenames as a dumb pile of bytes.
What do you do when the input isn't a dumb pile of bytes, but actual text? (Like from a text box the user typed into?)
The point I'm trying to get at being, you need to worry about the representation at multiple layers, not just at the bottom FS layer.
I have just been arguing the same thing in far too much detail in this thread: https://news.ycombinator.com/item?id=29722019
In Japanese, くるま, クルマ, and 車 are all the same word (the first two are the phonetic spelling "kuruma", the later is the Chinese character). However in order to know that 車 is read くるま you need to be a native Japanese speaker (or have a dictionary) -- should filesystems have dictionaries to match what a human would think? Search engines that support Japanese have to handle this to some degree, but I humbly suggest implement Google Search's language handling code into a filesystem would be an ill-advised decision.
If you wanted to implement the most minimal version of this you would map between katakana and hiragana, but that means you'll need to do this for other languages. For instance, Serbian. Serbian uses two scripts (both of which have upper and lower case forms) and any native Serbian speaker would see "tuđa ljuta paprika" and "туђа љута паприка" as the same text (note that lj became љ). Should that also be automatically translated in the filesystem?
In German, capitalisation is not reversible. ß becomes SS when capitalised but will be lowercased as ss. (There is now a capital version -- ẞ -- but from what I gather it's not widely used.)
Even in English you have British and American spellings of a given word -- native speakers would recognise them as the same thing but it would not be reasonable to expect a filesystem to map them to the same thing. Initialisms can have different identical representations (N.S.A vs NSA). And you also have cases where capitalisation actually does distinguish words (May vs may, PRISM vs prism, CAT vs cat, etc). What about fullwidth and halfwidth latin characters (Ｈｅｌｌｏ vs Hello)? Arguably those are even more identical than upper and lower case.
For all of the above reasons, case insensitivity is something which most systems will only ever implement for English and a few other European languages, meaning that it's more of a wart than a fully-working feature. If the argument really is "well, a human would recognise these two names as the same thing, so the filesystem should too" then why are none of the other examples given above handled? If it's too difficult to do correctly (which is my view) then why support any of this in the first place? However, everything should be normalised (NFC or NFD depending on your usecase).
I don't think I've seen any good argument against normalization, though.
I don't know about anyone else, but I read WORD as someone yelling, Word as designating/specifying a "word" with some importance, and woRD as the mocking Spongebob meme. I absolutely don't read "case insensitive" and I don't think filesystems should either.
Imagine if you could only search for ‘dog’ if you had to specify whether the author yelled it or not before you could find it.
Dog in bold, italics, red, green, uppercase, lowercase, initialcaps, smallcaps, are all the same word. What "the same" means has fuzzy boundaries and sometimes needs very precise specification, but I personally want the default to be the fuzzy convenient and the hyper-literal to be available as a fallback.
[I notice that I used 'color' and 'colour' here. My native language is UK English and programming languages and much of the internet use US English. I'm not sure if I would want `vim colour.txt` to open `color.txt`. Probably not. PowerShell 7 has a suggestions feature for "you typed a command which wasn't found, here are the most similar command names:" - mentioned in https://github.com/PowerShell/PowerShell/issues/10546 ]
But that is a feature of the word Dog, try the German words maßen (limited amounts) and massen (large amounts), historically they share the same upper case rendering MASSEN. Now someone versed in German could change to the alternative MASZEN or use the rather modern upper case version of ß. However the default naive (and most of the time correct) conversion between cases looses a significant amount of information.
What about people who CAN read English that way, but think having to match case when searching or referencing text hinders more than it helps?
Only if different case-variants do not have meaning. When two words that differ only in case have different meaning, we distinguish them (e.g. "moon" and "Moon").
Meaning doesn't go when the case changes in anything like the way meaning goes when the letters change. "neil armstrong was the first human to walk on the roof" is a very different sentence, you can't get anything like that difference with just case changes. If I spoke it, you wouldn't be able to tell if I spoke the correct case or not. Would you want school children searching for "one small step for man, one giant leap for mankind" and Google says "no results" because they used a lowercase m in mankind? Would you want a TV quiz show asking "What is Europa?" and a contenstant answers "a moon of jupiter" and the host asks "do you mean moon with a capital m or lowercase m?" before they decide whether the answer is correct?
Sorry to say I tend to use case sensitivity as a filter for me offering support to other developers. I'm not willing to find time for people who can't get their head around "turn on/off caps lock". You don't do it in professional writeups or applications (and I hope not in a CV) so don't pollute my filesystems or codebases with that madness.
If the mapping is non trivial then unless you're careful you end up breaking basic consistency between input and stored data hence the weird issues with mangling the unicode chars. If the mapping is trivial theres almost nothing to discuss. If the mapping is many to many you're going to have a bad time unless your consistent with your use of the maps. Then the fun is broken mappings where you get data loss due to incorrect many to one and one to many mappings.
There are times when caps matter, I e. code and filesystems are human readable so should not be arbitrary, but searching these for instance makes sense to be insensitive when needed (perhaps even default)
Second one: no, emails are not filenames, and more generally distinguishability is more important for identifiers. In cases where identifiers like emails need to be mapped to filenames, like caches, they should be normalized.
Case (in)sensitivity for filenames is a non-issue in my experience. Never had problems with either convention. As for emails, I do think insensitivity was the right choice.
The local-part of a mailbox MUST BE treated as case sensitive.
Section 2.4 RFC 2821, https://www.ietf.org/rfc/rfc2821.txt
do capital letters have a good enough usage case to justify their continued existence?
The same applies for a.txt and A.txt on case insensitive file systems (as someone pointed out the most common desktop file systems are).
[0]: https://forum.duolingo.com/comment/17787660/Bug-Correct-Viet...
But even worse than that is Python's NFKC, which normalizes ℌ to H and so on. The recommended normalizations are NFC for offline normalization (like in compiled languages and databases) and NFD for online, where speed trump's space. unicode.org talking that much about NFKC was a big mistake. NFKC is crazy and doesn't even roundtrip. The whole TR31 XID_Start/Continue sets are mostly because of NFKC issues, not so about stability. But people bought it for its stability argument.
I'm just writing a library and linter for such issues: https://github.com/rurban/libu8ident
Also note that C++23 will most likely enforce NFC identifiers only. Same problem as with this filesystem. My implementation was to accept all normal. forms and store it internally and in the object files as NFC. The C ABI should declare it also. Currently they don't care as much as Linux filesystems: Nada. Identifiers being unidentifiable
Nope, the lack of normalization on both accounts by the SMB server caused the issue. It could have normalized before emitting but it definitely should have normalized on receiving for comparison.
The problem are the compatible variants, NFKC and NFKD. But then you have usecases where you need them, and more to actually find strings. Levenshtein should not be the default when searching for strings.
"If you vote for my nutburger glyph my kid drew for a kindergarten assignment, I'll vote for the chicken scratching you noticed in the barnyard dust."
XML does not require normalisation: per <https://www.w3.org/TR/xml11/#sec-normalization-checking>, XML data SHOULD be fully normalised, but MUST NOT be transformed by processors; in other words, it’s a dead letter “SHOULD”, and no one actually cares, just like almost everything else.
The first line of Genesis reads thus: (from right-to-left, although the earliest Hebrew is actually LTR) בְּרֵאשִׁית, בָּרָא אֱלֹהִים, אֵת הַשָּׁמַיִם, וְאֵת הָאָרֶץ.
And the beginning of the Gospel of Mark thus: Ἀρχὴ τοῦ εὐαγγελίου Ἰησοῦ Χριστοῦ υἱοῦ θεοῦ.
(and if we're getting super technical there are a bunch of Aramaic phrases in the Bible that Jesus spoke, although I know little of Aramaic and I don't know how it would have been written in Biblical times between the Greek characters)
So the Lord would be needing those 16-bits after all..
Additionally there are (iirc) multiple ways to encode characters even in the ASCII set.
This is purely a failing in consistent normalization schemes.