What does the \u{...} notation mean in UNICODE and why are only some characters displayed like this in the CLDR project? - unicode

Question

In this link you will find the most used characters for each language. Why are some characters in some languages displayed under the \u{...} notation?
I think that what is in the brackets is the hexadecimal code of the character, but I can't understand why they would only do it with some characters.

Answer 1

The character sequences enclosed in curly brackets {} are digraphs (trigraphs, …) counted as a distinct letter in given language (supposedly with its own place in the alphabet), for instance
digraph {ch} in cs (Czech language);
trigraph {dzs} in hu (Hungarian alphabet);
more complex digraph examples in kkj (Kako language) shows the following Python code snippet:
>>> kkj='[a á à â {a\u0327} b ɓ c d ɗ {ɗy} e é è ê ɛ {ɛ\u0301} {ɛ\u0300} {ɛ\u0302} {ɛ\u0327} f g {gb} {gw} h i í ì î {i\u0327} j k {kp} {kw} l m {mb} n {nd} nj {ny} ŋ {ŋg} {ŋgb} {ŋgw} o ó ò ô ɔ {ɔ\u0301} {ɔ\u0300} {ɔ\u0302} {ɔ\u0327} p r s t u ú ù û {u\u0327} v w y]'
>>> print( kkj)
[a á à â {a̧} b ɓ c d ɗ {ɗy} e é è ê ɛ {ɛ́} {ɛ̀} {ɛ̂} {ɛ̧} f g {gb} {gw} h i í ì î {i̧} j k {kp} {kw} l m {mb} n {nd} nj {ny} ŋ {ŋg} {ŋgb} {ŋgw} o ó ò ô ɔ {ɔ́} {ɔ̀} {ɔ̂} {ɔ̧} p r s t u ú ù û {u̧} v w y]
>>>
For instance, {a\u0327} renders as {a̧} i.e. something like Latin Small Letter A with Combining Cedilla which has no Unicode equivalent. A counterexample:
ņ (U+0146) Latin Small Letter N With Cedilla with decomposition 004E 0327:
>>> import unicodedata
>>> print( 'ņ', unicodedata.normalize('NFC','{n\u0327}'))
ņ {ņ}
Edit:
Characters presented as unicode literals (\uxxxx = a character with 16-bit hex value xxxx) are unrenderable ones (or hard to render, at least). The following Python script shows some of them (Bidi_Class Values L-Left_To_Right, R-Right_To_Left, NSM-Nonspacing_Mark, BN-Boundary_Neutral):
# -*- coding: utf-8 -*-
import unicodedata
pa = 'ੱੰ਼੍ੁੂੇੈੋੌ'
pa = '\u0327 \u0A71 \u0A70 \u0A3C ੦ ੧ ੨ ੩ ੪ ੫ ੬ ੭ ੮ ੯ ੴ ੳ ਉ ਊ ਓ ਅ ਆ ਐ ਔ ੲ ਇ ਈ ਏ ਸ {ਸ\u0A3C} ਹ ਕ ਖ {ਖ\u0A3C} ਗ {ਗ\u0A3C} ਘ ਙ ਚ ਛ ਜ {ਜ\u0A3C} ਝ ਞ ਟ ਠ ਡ ਢ ਣ ਤ ਥ ਦ ਧ ਨ ਪ ਫ {ਫ\u0A3C} ਬ ਭ ਮ ਯ ਰ ਲ ਵ ੜ \u0A4D ਾ ਿ ੀ \u0A41 \u0A42 \u0A47 \u0A48 \u0A4B \u0A4C'
pa = '\u0300 \u0301 \u0302 \u1DC6 \u1DC7 \u0A71 \u0A70 \u0A3C \u0A4D \u0A41 \u0A42 \u0A47 \u0A48 \u0A4B \u0A4C \u05B7 \u05B8 \u05BF \u200C \u200D \u200E \u200F \u064B \u064C \u064E \u064F \u0650'
# above examples from ·kkj· ·bas· ·pa· ·yi· ·kn· ·ur· ·mzn·
print( pa )
for chr in pa:
if chr != ' ':
if chr == '{' or chr == '}':
print( chr )
else:
print( '\\u%04x' % ord(chr), chr,
unicodedata.category(chr),
unicodedata.bidirectional(chr) + '\t',
str( unicodedata.combining(chr)) + '\t',
unicodedata.name(chr, '?') )
Result: .\SO\63659122.py
̀ ́ ̂ ᷆ ᷇ ੱ ੰ ਼ ੍ ੁ ੂ ੇ ੈ ੋ ੌ ַ ָ ֿ ‌ ‍ ‎ ‏ ً ٌ َ ُ ِ
\u0300 ̀ Mn NSM 230 COMBINING GRAVE ACCENT
\u0301 ́ Mn NSM 230 COMBINING ACUTE ACCENT
\u0302 ̂ Mn NSM 230 COMBINING CIRCUMFLEX ACCENT
\u1dc6 ᷆ Mn NSM 230 COMBINING MACRON-GRAVE
\u1dc7 ᷇ Mn NSM 230 COMBINING ACUTE-MACRON
\u0a71 ੱ Mn NSM 0 GURMUKHI ADDAK
\u0a70 ੰ Mn NSM 0 GURMUKHI TIPPI
\u0a3c ਼ Mn NSM 7 GURMUKHI SIGN NUKTA
\u0a4d ੍ Mn NSM 9 GURMUKHI SIGN VIRAMA
\u0a41 ੁ Mn NSM 0 GURMUKHI VOWEL SIGN U
\u0a42 ੂ Mn NSM 0 GURMUKHI VOWEL SIGN UU
\u0a47 ੇ Mn NSM 0 GURMUKHI VOWEL SIGN EE
\u0a48 ੈ Mn NSM 0 GURMUKHI VOWEL SIGN AI
\u0a4b ੋ Mn NSM 0 GURMUKHI VOWEL SIGN OO
\u0a4c ੌ Mn NSM 0 GURMUKHI VOWEL SIGN AU
\u05b7 ַ Mn NSM 17 HEBREW POINT PATAH
\u05b8 ָ Mn NSM 18 HEBREW POINT QAMATS
\u05bf ֿ Mn NSM 23 HEBREW POINT RAFE
\u200c ‌ Cf BN 0 ZERO WIDTH NON-JOINER
\u200d ‍ Cf BN 0 ZERO WIDTH JOINER
\u200e ‎ Cf L 0 LEFT-TO-RIGHT MARK
\u200f ‏ Cf R 0 RIGHT-TO-LEFT MARK
\u064b ً Mn NSM 27 ARABIC FATHATAN
\u064c ٌ Mn NSM 28 ARABIC DAMMATAN
\u064e َ Mn NSM 30 ARABIC FATHA
\u064f ُ Mn NSM 31 ARABIC DAMMA
\u0650 ِ Mn NSM 32 ARABIC KASRA

Answer 2

It seems like all codepoints that don't have a well-defined stand-alone look (or are not meant to be used as stand-alone characters) are represented with this notation.
For example U+0A3C is present in the "character" {ਫ\u0A3C}. U+0A3C is a combining codepoint that modifies the one that is before it.