Unicode guide: Difference between revisions
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* Properties for each character | * Properties for each character | ||
* How to encode characters for storage | * How to encode characters for storage | ||
* How to normalize characters in to a canonical | * How to normalize characters in to a canonical format | ||
* How to segment text in to words, sentences, lines, and paragraphs | * How to segment text in to words, sentences, lines, and paragraphs | ||
* How to map text between different cases | * How to map text between different cases | ||
Revision as of 09:14, 30 September 2022
This is a WIP page, take nothing here as final.
Introduction
There's a lot of information out on the Internet about Unicode. Generally it falls in to a few separate categories:
- How Unicode has lots of characters
- How Unicode is unintuitive
- How new programming languages make ignoring Unicode easier
- How to encode Unicode characters
- standards are the source
- explain this is a guide or on ramp
What is Unicode?
Before I get in to the main article I'd like to provide a quick overview of what Unicode is.
Unicode defines the following:
- A large multilingual set of abstract characters (known just as 'characters')
- Properties for each character
- How to encode characters for storage
- How to normalize characters in to a canonical format
- How to segment text in to words, sentences, lines, and paragraphs
- How to map text between different cases
- How to order text for sorting
- How to match text for searching
- How to incorporate Unicode in to regular expressions
Many of these can be further tailored by locale-dependent rules and custom algorithms.
The layered model
- 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
- The Unicode Standard, Version 15.0 chapters 1, 2, 3, 4 and 23
- Unicode Glossary
- Unicode Technical Reports
- Unicode Frequently Asked Questions
You might also find the following tools helpful:
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.