Unicode guide

This is a WIP page, take nothing here as final.

If you've ever tried to learn Unicode you've most likely looked at online tutorial and learning resources. These tend to focus on specific details about how Unicode works instead of the broader picture.

This guide is my attempt to help you build a mental model of Unicode that can be used to write functional software and navigate the official Unicode standards and resources.

As a disclaimer: I'm just a random person, some of this might be wrong. But hopefully by the end of reading this you should be able to correct me.

Standards

The Unicode standard defines the following:

• A large multilingual set of abstract characters (known just as 'characters')
• A database of properties for each character
• How to encode and decode characters to bytes
• How to normalize equivalent sequences of characters
• How to map text between different cases
• How to segment text in to words, sentences, lines, and paragraphs
• How to determine text direction

Some portions of the standard may be overridden (also known as 'tailoring') to aid in localization.

TODO:

These standards are freely available online.

- The Core Specification https://www.unicode.org/versions/latest/

- Unicode Standard Annexes https://www.unicode.org/reports/index.html#annexes

• How to order text for sorting

• How to incorporate Unicode in to regular expressions

Technical Standards https://www.unicode.org/reports/index.html#standards

CLDR https://cldr.unicode.org/index

https://www.unicode.org/policies/

What are characters?

TODO

What are strings?

- levels of abstraction

- indexing

- sort

- match

- search

- normalize

- serialize

- case map

- properties

- breaking/segmentation

- reversing

Level 1: Bytes

level 1: bytes. you can compare, search, splitting, sorting. your basic unit is the byte

filesystem/unix/C

Level 2: Code units

level 2: code units. your basic unit is the smallest unit of your unicode encoding: a byte for utf-8, a 16-bit int for UTF-16, a 32-bit int for UTF-32. you can compare, search, splitting, sort. to get to this point you have to handle endianness

windows

Level 3: Unicode scalars

level 3: unicode scalars. your basic unit is a number between 0x0 and 0x1fffff inclusive, with some ranges for surrogates not allowed. to get tho this point you have to decode utf-8, utf-16 or utf-32. you can compare, search, split, etc but it's important to note that these are just numbers. there's no meaning attached to them

python

Level 4: Unicode characters

level 4: unicode characters: your basic unit is a code point that your runtime recognizes and is willing to interpret using a copy of the unicode database. results vary according to the supported unicode version. you can normalize, compare, match, search, and splitting, case map strings. locale specific operations may be provided. to get these the runtime needs to check if the characters are supported.

???

Level 5: Segmented text

level 5: unicode texts: your basic unit is a string of unicode characters of some amount, such as a word, paragraph, grapheme cluster. to get these you need to convert from a string of unicode characters with breaking/segmentation rules

swift/raku

Further reading

I highly recommend reading the following resources

1. The Unicode Standard, Version 15.0 chapters 1, 2, 3, 4 and 23
2. Unicode Glossary
3. Unicode Technical Reports
4. Unicode Frequently Asked Questions

You might also find the following tools helpful:

• Unicode Utilities
• Unicode Code Charts
• Unicode Character Database

The Unicode Common Locale Data Repository provides locale-specific information that aids in this tailoring Unicode algorithms and other localization tasks.

TODO:

languages/locales

Non-Unicode compatibility

- preserving data

- While writing this page I researched and documented Unicode support in various programming languages. You can see my notes here: Unicode guide/Implementations.