Upper and lowercase t

 m

1. bread

Inflection[edit]

Declension of t (masculine)

Alternative forms[edit]

Alternative hieroglyphic writings of t  

Derived terms[edit]

• t ꜣšr
• t-ḥḏ

Esperanto[edit]

Pronunciation[edit]

• (letter name): IPA^(key): /to/
• (phoneme): IPA^(key): /t/

• Audio

  (file)

Letter[edit]

t (lower case, upper case T)

1. The twenty-fourth letter of the Esperanto alphabet, called to and written in the Latin script.

See also[edit]

• (Latin-script letters) litero; A a, B b, C c, Ĉ ĉ, D d, E e, F f, G g, Ĝ ĝ, H h, Ĥ ĥ, I i, J j, Ĵ ĵ, K k, L l, M m, N n, O o, P p, R r, S s, Ŝ ŝ, T t, U u, Ŭ ŭ, V v, Z z

Faroese[edit]

Pronunciation[edit]

• IPA^(key): /tʰ/

Letter[edit]

t (upper case T)

1. The twenty-second letter of the Faroese alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) bókstavur; A a, Á á, B b, D d, Рð, E e, F f, G g, H h, I i, Í í, J j, K k, L l, M m, N n, O o, Ó ó, P p, R r, S s, T t, U u, Ú ú, V v, Y y, Ý ý, Æ æ, Ø ø

Finnish[edit]

Pronunciation[edit]

• Audio

  (file)

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the Finnish alphabet, called tee and written in the Latin script.

See also[edit]

• (Latin-script letters) kirjain; A a, B b, C c, D d, E e, F f, G g, H h, I i, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s (Š š), T t, U u, V v (W w), X x, Y y, Z z (Ž ž), Å å, Ä ä, Ö ö

Noun[edit]

t

1. Abbreviation of tavu.

Etymology[edit]

Pronunciation[edit]

• (letter name) IPA^(key): /te/

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the French alphabet, written in the Latin script.

Contraction[edit]

t

1. (text messaging, Internet slang) Informal spelling of t'es

See also[edit]

• -t-
• t'

Pronunciation[edit]

• IPA^(key): /t/

Letter[edit]

t (lower case, upper case T)

1. A letter of the Fula alphabet, written in the Latin script.

Usage notes[edit]

• Common to all varieties of Fula (Fulfulde / Pulaar / Pular).

See also[edit]

• (Latin-script letters) karfeeje; ', A a, B b, Mb mb, Ɓ ɓ, C c, D d, Nd nd, Ɗ ɗ, E e, F f, G g, Ng ng, Ɠ ɠ, H h, I i, J j, Nj nj, K k, L l, M m, N n, Ŋ ŋ, Ñ ñ, Ɲ ɲ, O o, P p, R r, S s, T t, U u, W w, Y y, Ƴ ƴ

Pronunciation[edit]

• Audio

  (file)

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the German alphabet, called te and written in the Latin script.

Derived terms[edit]

• Wohlklangs-t

Related terms[edit]

• t euphonicum

Romanization[edit]

t

1. Romanization of 𐍄

Hungarian[edit]

Pronunciation[edit]

• (phoneme): IPA^(key): [ˈt]
• (letter name): IPA^(key): [ˈteː]

Letter[edit]

t (lower case, upper case T)

1. The thirty-second letter of the Hungarian alphabet, called té and written in the Latin script.

Declension[edit]

Possessive forms of t
possessor	single possession	multiple possessions
1st person sing.	t-m	t-im
2nd person sing.	t-d	t-id
3rd person sing.	t-je	t-i
1st person plural	t-nk	t-ink
2nd person plural	t-tek	t-itek
3rd person plural	t-jük	t-ik

See also[edit]

• (Latin-script letters) betű; A a, Á á, B b, C c, Cs cs, D d, Dz dz, Dzs dzs, E e, É é, F f, G g, Gy gy, H h, I i, Í í, J j, K k, L l, Ly ly, M m, N n, Ny ny, O o, Ó ó, Ö ö, Ő ő, P p, R r, S s, Sz sz, T t, Ty ty, U u, Ú ú, Ü ü, Ű ű, V v, Z z, Zs zs. Only in the extended alphabet: Q q W w X x Y y. Commonly used: ch. Also defined: à ë. In surnames (selection): ä aa cz ds eé eö ew oe oó th ts ÿ.

Further reading[edit]

• t in Bárczi, Géza and László Országh. A magyar nyelv értelmező szótára (‘The Explanatory Dictionary of the Hungarian Language’). Budapest: Akadémiai Kiadó, 1959–1962. Fifth ed., 1992: →ISBN

Pronunciation[edit]

• (context pronunciation) IPA^(key): /t/
• (letter name) IPA^(key): /te/

Letter[edit]

t (upper case T)

1. The twentieth letter of the Ido alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) litero; A a, B b, C c, D d, E e, F f, G g, H h, I i, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s, T t, U u, V v, W w, X x, Y y, Z z

Italian[edit]

Letter[edit]

t m or f (invariable)

1. see under T

Letter[edit]

t

1. A letter of the Latin alphabet.

References[edit]

• t in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)

Latvian[edit]

Latvian Wikipedia has an article on:

t

Wikipedia ^lv

Etymology[edit]

Proposed in 1908 as part of the new Latvian spelling by the scientific commission headed by K. Mīlenbahs, which was accepted and began to be taught in schools in 1909. Prior to that, Latvian had been written in German Fraktur, and sporadically in Cyrillic.

Pronunciation[edit]

• IPA^(key): [t]

Letter[edit]

t (lower case, upper case T)

1. The twenty-eighth letter of the Latvian alphabet, called tē and written in the Latin script.

See also[edit]

• Letters of the Latvian alphabet:

  burti: Aa, Āā, Bb, Cc, Čč, Dd, Ee, Ēē, Ff, Gg, Ģģ, Hh, Ii, Īī, Jj, Kk, Ķķ, Ll, Ļļ, Mm, Nn, Ņņ, Oo, Pp, Rr, Ss, Šš, Tt, Uu, Ūū, Vv, Zz, Žž

Livonian[edit]

Pronunciation[edit]

• (phoneme) IPA^(key): /t̪/

Letter[edit]

t (upper case T)

1. The thirty-third letter of the Livonian alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) kēratēḑ; A a, Ā ā, Ä ä, Ǟ ǟ, B b, D d, Ḑ ḑ, E e, Ē ē, F f, G g, H h, I i, Ī ī, J j, K k, L l, Ļ ļ, M m, N n, Ņ ņ, O o, Ō ō, Ȯ ȯ, Ȱ ȱ, Õ õ, Ȭ ȭ, P p, R r, Ŗ ŗ, S s, Š š, T t, Ț ț, U u, Ū ū, V v, Z z, Ž ž

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the Malay alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) A a, B b, C c, D d, E e, F f, G g, H h, I i, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s, T t, U u, V v, W w, X x, Y y, Z z

Maltese[edit]

Pronunciation[edit]

• IPA^(key): /t/
• IPA^(key): /d/ (by assimilation to a following voiced obstruent)

Letter[edit]

t (lower case, upper case T)

1. The twenty-fourth letter of the Maltese alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) ittra; A a, B b, Ċ ċ, D d, E e, F f, Ġ ġ, G g, Għ għ, H h, Ħ ħ, I i, Ie ie, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s, T t, U u, V v, W w, X x, Ż ż, Z z

Norwegian Bokmål[edit]

Pronunciation[edit]

• (letter name): IPA^(key): /teː/
• (phoneme): IPA^(key): /t/, (in rt) /ʈ/

• Audio

  (file)

Letter[edit]

t

1. The 20th letter of the Norwegian alphabet.

Norwegian Nynorsk[edit]

Norwegian Nynorsk Wikipedia has an article on:

T

Wikipedia ⁿⁿ

Etymology 1[edit]

Pronunciation[edit]

• (letter name): IPA^(key): /teː/
• (phoneme): IPA^(key): /t/, (in rt) /ʈ/

• Audio

  (file)

Letter[edit]

t m (upper case T, definite singular t-en, indefinite plural t-ar, definite plural t-ane)

1. The 20th letter of the Norwegian alphabet.
2. Something in the shape of a T

Etymology 2[edit]

Noun[edit]

t

1. Abbreviation of time.
2. Abbreviation of tonn.
3. (music) Abbreviation of tempo.
4. (music) Abbreviation of tenor.
5. (historical) Initialism of tilfredsstillande (academic grade).
6. Abbreviation of tara.
7. (music) Abbreviation of tonika (“tonic”).

Preposition[edit]

t

1. (text messaging, informal) Abbreviation of til (“to”).

References[edit]

• “t” in The Nynorsk Dictionary.

Pronunciation[edit]

• (phoneme): IPA^(key): /t/

Letter[edit]

t (lower case, upper case T)

1. The twenty-third letter of the Nupe alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) banki; A a (Á á, À à), B b, C c, D d, Dz dz, E e (É é, È è), F f, G g, Gb gb, H h, I i (Í í, Ì ì), J j, K k, Kp kp, L l, M m (Ḿ ḿ, M̀ m̀, M̄ m̄), N n (Ń ń, Ǹ ǹ, N̄ n̄), O o (Ó ó, Ò ò), P p, R r, S s, Sh sh, T t, Ts ts, U u (Ú ú, Ù ù), V v, W w, Y y, Z z, Zh zh

Pronunciation[edit]

• IPA^(key): /tɛ/

Letter[edit]

t (upper case T, lower case)

1. The twenty-sixth letter of the Polish alphabet, called te and written in the Latin script.

See also[edit]

• (Latin-script letters) A a, Ą ą, B b, C c, Ć ć, D d, E e, Ę ę, F f, G g, H h, I i, J j, K k, L l, Ł ł, M m, N n, Ń ń, O o, Ó ó, P p (Q q), R r, S s, Ś ś, T t, U u (V v), W w (X x), Y y, Z z, Ź ź, Ż ż

Further reading[edit]

• t in Wielki słownik języka polskiego, Instytut Języka Polskiego PAN
• t in Polish dictionaries at PWN

Portuguese[edit]

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the Portuguese alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) letra; A a (Á á, À à,  â, àã), B b, C c (Ç ç), D d, E e (É é, Ê ê), F f, G g, H h, I i (Í í), J j, K k, L l, M m, N n, O o (Ó ó, Ô ô, Õ õ), P p, Q q, R r, S s, T t, U u (Ú ú), V v, W w, X x, Y y, Z z

Pronunciation[edit]

• IPA^(key): /t/

Letter[edit]

t (lower case, upper case T)

1. (International Standard) The twenty-sixth letter of the Romani alphabet, written in the Latin script.
2. (Pan-Vlax) The twenty-seventh letter of the Romani alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) A a, B b, C c, D d, E e, F f, G g, H h, X x, I i, J j, K k, Kh kh, L l, M m, N n, O o, P p, Ph ph, R r, S s, T t, Th th, U u, V v, Z z International Standard: (À à, Ä ä, Ǎ ǎ), Ć ć, Ćh ćh, (È è, Ë ë, Ě ě), (Ì ì, Ï ï, Ǐ ǐ), (Ò ò, Ö ö, Ǒ ǒ), Rr rr, Ś ś, (Ù ù, Ü ü, Ǔ ǔ), Ź ź, Ʒ ʒ, Q q, Ç ç, ϴ θ. Pan-Vlax: Č č, Čh čh, Dž dž, (Dź dź), Ř ř, Š š, (Ś ś), Ž ž, (Ź ź).

Romanian[edit]

Pronunciation[edit]

• IPA^(key): /t/

Letter[edit]

t (lower case, upper case T)

1. The twenty-fourth letter of the Romanian alphabet, called te or tî and written in the Latin script.

See also[edit]

• (Latin-script letters) A a, Ă ă,  â, B b, C c, D d, E e, F f, G g, H h, I i, Πî, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s, Ș ș, T t, Ț ț, U u, V v, W w, X x, Y y, Z z

Saterland Frisian[edit]

Pronunciation[edit]

• IPA^(key): /ət/
• Hyphenation: t

Article[edit]

t

1. Unstressed form of dät

References[edit]

• Pyt Kramer (1996) Kute Seelter Sproakleere‎^[1], Mildam, page 10

Serbo-Croatian[edit]

Alternative forms[edit]

• (uppercase) T

Pronunciation[edit]

• (phoneme) IPA^(key): /t/

Letter[edit]

t (Cyrillic spelling т)

1. The 26th letter of the Serbo-Croatian Latin alphabet (gajica), preceded by š and followed by u.

Skolt Sami[edit]

Pronunciation[edit]

• (phoneme) IPA^(key): /t/

Letter[edit]

t (upper case T)

1. The thirtieth letter of the Skolt Sami alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) bukva; A a,  â, B b, C c, Č č, Ʒ ʒ, Ǯ ǯ, D d, Đ đ, E e, F f, G g, Ǧ ǧ, Ǥ ǥ, H h, I i, J j, K k, Ǩ ǩ, L l, M m, N n, Ŋ ŋ, O o, Õ õ, P p, R r, S s, Š š, T t, U u, V v, Z z, Ž ž, Å å, Ä ä, ʹ

Spanish[edit]

Pronunciation[edit]

• (phoneme) IPA^(key): /t/

• (letter name) IPA^(key): /ˈte/, [ˈt̪e]

  • Audio (Spain)

    (file)

Letter[edit]

t (lower case, upper case T)

1. the 21st letter of the Spanish alphabet

Swedish[edit]

Pronunciation[edit]

• IPA^(key): /teː/

• audio

  (file)

• Homophones: T, te
• Rhymes: -eː

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the Swedish alphabet

Declension[edit]

Turkish[edit]

Letter[edit]

t (lower case, upper case T)

1. The twenty-fourth letter of the Turkish alphabet, called te and written in the Latin script.

See also[edit]

• (Latin-script letters) harf; A a, B b, C c, Ç ç, D d, E e, F f, G g, Ğ ğ, H h, I ı, İ i, J j, K k, L l, M m, N n, O o, Ö ö, P p, R r, S s, Ş ş, T t, U u, Ü ü, V v, Y y, Z z

Turkmen[edit]

Pronunciation[edit]

• (phoneme) IPA^(key): /t/

Letter[edit]

t (upper case T)

1. The twenty-fourth letter of the Turkmen alphabet, called te and written in the Latin script.

See also[edit]

• (Latin-script letters) harp; A a, B b, Ç ç, D d, E e, Ä ä, F f, G g, H h, I i, J j, Ž ž, K k, L l, M m, N n, Ň ň, O o, Ö ö, P p, R r, S s, Ş ş, T t, U u, Ü ü, W w, Y y, Ý ý, Z z

Pronunciation[edit]

• (phoneme): IPA^(key): /t/
• (letter name): IPA^(key): /tí/

Letter[edit]

t (lower case, upper case T)

1. The twenty-second letter of the Yoruba alphabet, called tí and written in the Latin script.

See also[edit]

• (Latin-script letters) lẹ́tà; A a (Á á, À à, Ā ā), B b, D d, E e (É é, È è, Ē ē), Ẹ ẹ (Ẹ́ ẹ́, Ẹ̀ ẹ̀, Ẹ̄ ẹ̄), F f, G g, Gb gb, H h, I i (Í í, Ì ì, Ī ī), J j, K k, L l, M m (Ḿ ḿ, M̀ m̀, M̄ m̄), N n (Ń ń, Ǹ ǹ, N̄ n̄), O o (Ó ó, Ò ò, Ō ō), Ọ ọ (Ọ́ ọ́, Ọ̀ ọ̀, Ọ̄ ọ̄), P p, R r, S s, Ṣ ṣ, T t, U u (Ú ú, Ù ù, Ū ū), W w, Y y

• As used in Benin: (Latin-script letters) lɛ́tà; A a, B b, D d, E e, Ɛ ɛ, F f, G g, Gb gb, H h, I i, J j, K k, Kp kp, L l, M m, N n, O o, Ɔ ɔ, P p, R r, S s, Sh sh, T t, U u, W w, Y y

Letter[edit]

t (lower case, upper case T)

1. The twentieth letter of the Zulu alphabet, written in the Latin script.

See also[edit]

• (Latin-script letters) A a, B b, C c, D d, E e, F f, G g, H h, I i, J j, K k, L l, M m, N n, O o, P p, Q q, R r, S s, T t, U u, V v, W w, X x, Y y, Z z

The truth about character case that programmers need to know / Habr

At the North Bay Python conference in 2018, I gave a talk on usernames. Most of the information in the report was compiled by me over 12 years of maintaining django-registration. This experience gave me a lot more knowledge than I had planned to have on how complex "simple" things can be.

At the beginning of the report, I did mention that this would not be another exposé from the series of "misconceptions about X that programmers believe." You can find any number of such revelations. However, I don't like these articles. They list various things that are allegedly false, but very rarely explain why this is so, and what should be done instead. I suspect that people will simply read articles like this, congratulate themselves on this achievement, and then go on to find new and interesting ways to make mistakes not mentioned in these articles. It's because they didn't really understand the problems that these bugs give rise to.

Therefore, in my report, I tried to explain some of the problems as best as possible and explain how to solve them - I like this approach much more. One topic that I've only touched on in passing (it was just one slide and a couple of mentions on other slides) is the complexities that can be associated with character case. There is an official Correct Answer™ for the problem I was discussing - comparing case-insensitive identifiers - and in the talk I gave the best solution I know, using only the Python standard library.

However, I briefly mentioned the deeper complications with Unicode case, and I want to spend some time describing the details. This is interesting, and understanding this can help you make decisions when designing and writing code that processes text. Therefore, I offer you something opposite to the articles "misconceptions about X that programmers believe" - ​​"the truth that programmers should know."

One more thing: Unicode is full of terminology. In this article, I will mainly use the definitions of "upper case" and "lower case" because the Unicode standard uses these terms. If you like other terms, like lowercase/uppercase letters, that's fine. Also, I will often use the term "symbol", which some may consider incorrect. Yes, in Unicode the concept of "character" isn't always what people expect, so it's often best to avoid it by using other terms. However, in this article, I will use the term as it is used in Unicode, to describe an abstract entity about which claims can be made. When it matters, I will use more specific terms like "code point" for clarification.

There are more than two registers

Speakers of European languages ​​are accustomed to using case in their languages ​​to denote specific things. For example, in English [and Russian] we usually start sentences with an uppercase letter and most often continue with lowercase letters. Also, proper nouns start with uppercase letters, and many acronyms and abbreviations are written in uppercase.

And we usually think that there are only two registers. There is an "A" and there is an "a". One is in upper case, the other is in lower case, isn't it?

However, there are three cases in Unicode. There is an upper one, there is a lower one, and there is a title case [titlecase]. In English, this is how names are written. For example, Avengers: Infinity War. Usually, to do this, the first letter of each word is simply written in uppercase (and depending on different rules and styles, some words, such as articles, are not capitalized).

The Unicode standard gives this example of a capital case character: U+01F2 LATIN CAPITAL LETTER D WITH SMALL Z. It looks like this: Dz.

Such characters are sometimes required to handle the negative consequences of one of the early design decisions of the Unicode standard: compatibility with existing text encodings in both directions. It would be more convenient for Unicode to compose sequences using the standard's character combination capabilities. However, in many systems already in existence, space has already been allocated for ready-made sequences. For example, in the ISO-8859-1 ("latin-1") standard, the character "é" has a prepared form numbered 0xe9. In Unicode, it would be preferable to write this letter with a separate "e" and an accent mark. But to ensure full compatibility in both directions with existing encodings such as latin-1, Unicode also assigns code points for predefined characters. For example, U+00E9 LATIN SMALL LETTER E WITH ACUTE.

Although this character's code position is the same as its latin-1 byte value, don't rely on it. It is unlikely that the character encoding in Unicode will retain these positions. For example, in UTF-8 code position U+00E9written as the byte sequence 0xc3 0xa9.

And, of course, there are characters in already existing encodings that needed special treatment when using title case, which is why they were included in Unicode "as is". If you want to look at them, search your favorite Unicode database for characters in the Lt ("Letter, titlecase") category.

There are several ways to determine the register

The Unicode Standard (§4. 2) lists three different definitions of case. Perhaps the choice of one of the three makes your programming language for you; otherwise, your choice will depend on the specific purpose. Here are the definitions:

1. A character is uppercase if it belongs to the category Lu ("Letter, uppercase"), and lowercase if it belongs to the category Ll ("Letter, lowercase"). The standard recognizes the limitations of this definition: each specific character has to be attributed to only one of the categories. Because of this, many characters that "should be" in upper or lower case will not meet this requirement because they belong to some other category.
2. The character is uppercase if it inherits the Uppercase property, and lowercase if it inherits the Lowercase property. It is a combination of defining one with other character properties, which may include case.
3. A character is in uppercase if it does not change after a case mapping to uppercase has been applied to it. A character is in lowercase if, after applying a lowercase case mapping to it, it does not change. A rather general definition, however, it can also behave non-intuitively.

If you are working with a limited subset of characters (specifically, letters), then 1 definition may be enough for you. If your repertoire is broader - it includes characters that look like letters that are not letters, the 2nd definition may suit you. It is also recommended by the Unicode standard, §4.2:

Programmers manipulating Unicode strings should work with string functions such as isLowerCase (and its functional cousin toLowerCase) if they do not operate on character properties directly.

The function mentioned here is defined in §3.13 of the Unicode Standard. Formally, the 3rd definition uses the isLowerCase and isUpperCase functions from §3.13, defined in terms of fixed positions in toLowerCase and toUpperCase, respectively.

If your programming language has functions for checking or converting the case of strings or individual characters, it's worth looking into which of the definitions mentioned are used in the implementation. If you're wondering, Python's isupper() and islower() methods use the 2nd definition.

Cannot understand the case of a character by its appearance or name

By the appearance of many characters, you can understand what case they are in. For example, "A" is in upper case. This is clear from the name of the symbol: "LATIN CAPITAL LETTER A". However, sometimes this method does not work. Let's take the code position U+1D34. It looks like this: ᴴ. In Unicode, it's assigned a name: MODIFIER LETTER CAPITAL H. So it's in uppercase, right?

In fact, it inherits the Lowercase property, so by definition #2 it is in lower case, despite the fact that it visually resembles a capital H, and the name contains the word "CAPITAL".

Some characters have no case at all

Definition 135 in §3.13 of the Unicode Standard reads:

The character C is case-sensitive if and only if C has a Lowercase or Uppercase property, or the value of the General_Category parameter is Titlecase_Letter.

So a lot of Unicode characters - in fact, most of them - are caseless. Questions about their case do not make sense, and case changes do not affect them. However, we can get the answer to this question by definition #3.

Some characters behave as if they have multiple cases

It follows from this that if you use definition #3 and ask if an uncase character is in uppercase or lowercase, you will get the answer "yes".

The Unicode standard gives an example (Table 4-1, line 7) of the U+02BD MODIFIER LETTER REVERSED COMMA character (which looks like this: ʽ). It does not have the inherited Lowercase or Uppercase properties, and is not in the Lt category, so it is not case-sensitive. However, converting to upper case does not change it, and converting to lower case does not change it, so by definition 3 it answers yes to both questions: "Are you upper case?" and “are you lowercase?”

This seems like a lot of unnecessary confusion, but the point is that definition #3 works with any sequence of Unicode characters, and simplifies case conversion algorithms (caseless characters just turn into themselves).

Case dependent on context

You might think that if the Unicode case conversion tables cover all characters, then this conversion is simply a matter of finding the right place in the table. For example, the Unicode database says that U+0041 LATIN CAPITAL LETTER A will be U+0061 LATIN SMALL LETTER A in lowercase. Simple, right?

One example where this approach does not work is Greek. The character Σ—that is, U+03A3 GREEK CAPITAL LETTER SIGMA—is mapped to two different characters when converted to lowercase, depending on where it appears in the word. If it is at the end of a word, then it will be ς (U+03C2 GREEK SMALL LETTER FINAL SIGMA) in lower case. Anywhere else it will be σ (U+03C3 GREEK SMALL LETTER SIGMA).

This means that the register has no one-to-one or transitivity. Another example is ß (U+00DF LATIN SMALL LETTER SHARP S, or escet). In uppercase it would be "SS", although there is now another uppercase form of it (ẞ, U+1E9E LATIN CAPITAL LETTER SHARP S). And converting "SS" to lowercase results in "ss", so (using Unicode terminology for case conversion): toLowerCase(toUpperCase(ß)) != ß.

Locale-specific case

Different languages ​​have different case conversion rules. The most popular example: i (U+0069 LATIN SMALL LETTER I) and I (U+0049 LATIN CAPITAL LETTER I) are converted to each other in most locales - most, but not all. In the az and tr locales (Turkic), the uppercase i is İ (U+0130 LATIN CAPITAL LETTER I WITH DOT ABOVE) and the lowercase I is ı (U+0131 LATIN SMALL LETTER DOTLESS I). Sometimes the right notation really means the difference between life and death.

Unicode itself does not handle all possible case conversion rules for all locales. In the Unicode database, there are only general rules for converting all characters that are not dependent on the locale. Also there are special rules for some languages ​​and compound forms - Lithuanian, Turkic languages, some features of Greek. Everything else is not there. §3.13 of the standard mentions this and recommends introducing locale-specific conversion rules when necessary.

One example that will be familiar to English speakers is the title case of certain names. "o'brian" must be converted to "O'Brian" (not to "O'brian"). However, in this case, "it's" must be converted to "It's", and not to "It's". Another example that is not handled in Unicode is the Dutch character "ij", which, when converted to title case, must be converted to uppercase if it appears at the beginning of a word. Thus, a large bay in the Netherlands would be "IJsselmeer" in the title case, not "Ijsselmeer". Unicode has the characters IJ U+0132 LATIN CAPITAL LIGATURE IJ and ij U+0133 LATIN SMALL LIGATURE IJ if you need them. By default, case conversion converts them to each other (although Unicode normalization forms using compatibility equivalence will split them into two separate characters).

Case-insensitive comparison requires folded case conversion

Returning to the material presented in the report. The complexity of dealing with case in Unicode means that case-insensitive comparison cannot be done using the standard lowercase or uppercase conversion functions found in many programming languages. For such comparisons, Unicode has the concept of case folding, and §3.13 of the standard defines the toCaseFold and isCaseFolded functions.

You might think that folding to folded case is like casting to lowercase, but it's not. The Unicode standard warns that a folded-case string will not necessarily be in lowercase. The Cherokee language is given as an example - there, in a line that is in folded case, characters in upper case will also come across.

One of the slides in my report implements the recommendations of Unicode Technical Report #36 in Python as fully as possible. NFKC is normalized and then the casefold() method (only available in Python 3+) is called on the resulting string. Even so, some edge cases fall out, and this is not exactly what is recommended for comparing identifiers. First, the bad news: Python doesn't expose enough Unicode properties to filter out characters that aren't in XID_Start or XID_Continue, or characters that have the Default_Ignorable_Code_Point property. To my knowledge it does not support NFKC_Casefold mapping. It also lacks an easy way to use the modified NFKC UAX #31§5.1.

The good news is that most of these edge cases do not involve any real security risks posed by the characters in question. And case folding is in principle not defined as a normalization-preserving operation (hence the NFKC_Casefold mapping, which renormalizes to NFC after case folding). Generally, when comparing, you don't care if both strings are normalized after preprocessing. What you care about is whether the preprocessing is inconsistent, and whether it guarantees that only strings that "should" be different afterwards will be different afterwards. If this bothers you, you can manually renormalize after case addition.

Enough for now

This article, like the previous report, is not exhaustive, and it is hardly possible to fit all this material into a single post. I hope this has been a useful overview of the complexities associated with this topic and that you will find enough starting points in it to look for further information. Therefore, in principle, you can stop here.

Wouldn't it be naïve for me to hope that other people would stop writing exposés from the series of "misconceptions about X that programmers believe" and start writing articles like "the truth programmers should know"?

LOWER (Transact-SQL) - SQL Server

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• Article
• 09/26/2022
• Reading takes 2 minutes

Scope: SQL Server (all supported versions) Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Platform System (PDW)

Returns a character expression after converting uppercase characters to lowercase characters.

Syntax notation in Transact-SQL

Syntax

 LOWER ( character_expression ) 

Note

For links to descriptions of the Transact-SQL syntax for SQL Server 2014 and earlier, see Legacy Documentation.

Arguments

character_expression
Character or binary data expression. character_expression can be a constant, variable or column. Argument character_expression must be of a data type that can be implicitly converted to type varchar . Otherwise, use CAST to explicitly convert character_expression .

Return types

varchar or nvarchar

Examples

The following example uses the LOWER 9 functions0162 and UPPER , with the UPPER function nested within the LOWER function, when selecting product names priced between $11 and $20.

 -- Uses AdventureWorks SELECT LOWER(SUBSTRING(EnglishProductName, 1, 20)) AS Lower, UPPER(SUBSTRING(EnglishProductName, 1, 20)) AS Upper, LOWER(UPPER(SUBSTRING(EnglishProductName, 1, 20))) As LowerUpper FROM dbo. 
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