Updated 2015-03-01 00:52:13 by AMG

Unicode is a standard for coding multingual text. ISO has standardized a portion of Unicode as ISO646

Reference  edit

The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!), Joel Spolsky, 2003-10-08
Characters and Combining Marks, The Unicode Consortium
If a programmer is going to read only one document summarizing Unicode this is the one to read. It presents the key terms, such as text element, character, code unit, code point, and grapheme cluster, canonical equivalence, and compatibility decomposition.
Unicode Standard Annex #29, Unicode Text Segmentation
another Unicode document that is particularly relevant to programmers.
ISO Standard 10646:2012 (and electronic inserts), Information technology -- Universal Coded Character Set (UCS)
The ISO standard based on the character coding portions of Unicode
ISO Amendment 10646:2012/Amd 1:2013 (and electronic inserts)
The first amendment to ISO646:2012
Book Review: Unicode Explained, by Jukka K. Korpela (alternate), Cameron Laird

See Also  edit

Unicode and UTF-8
Unicode file reader
A little Unicode editor
i18n tester
quickly shows what parts of Unicode are supported by your fonts
dead keys for accents
a tiny package allowing easier entering of accented characters
i18n - writing for the world
some random korean text

Resources  edit

Unicode fonts and tools for X11
The classic X bitmap fonts in an ISO 10646-1/Unicode extension
Multilingual Unicode TrueType Fonts on the Internet, Slavic Text Processing and Typography
links to free TrueType fonts for larger or smaller subsets of the Unicode.
Welcome to Computers and Writing Systems, SIL International
source of free Unicode fonts in various languages, with a particular focus on more obscure languages and local dialects.
I18n Guy
a website dedicated to program internationalization
Character Sets And Code Pages At The Push Of A Button, Tex Texin
code charts from all over.
ascii2uni and uni2ascii
bidirectional conversion between Unicode and more than thirty 7-bit ASCII equivalents, including RFC 2396 URI, RFC 2045 Quoted Printable format, and the \uXXXX notation used in Tcl
Deja Vu Fonts
a set of free fonts based on the Vera fonts, and providing a wider range of characters

Description  edit

Unicode is complex. Whereas ASCII defines 127 characters, Unicode defines 1,114,112 code points, and characters are composed of one or more code points. Unicode provides code charts, but doesn't stop there. The following things are also specified by Unicode:

  • character classes such as capitalization, and sort order
  • Rendering hints
  • composition of characters from individual codepoints, and decomposed into individual code points.
  • normalization of code-point sequences
  • hyphenation and line-breaking
  • boundaries of words and sentences
  • user interaction for processes such as text deletion and highlighting

RS: Until version 3.0, 16 bits (\u0000-\uFFFD: the "Basic Multilingual Plane", BMP) were sufficient for any Unicode. From 3.1, we must expect longer codes - up to 31 bits long, as specified in ISO 10646. Why 31 bits? Because that is the maximum that can be expressed in UTF-8: 6 bytes, omitting the taboo values \xFE and \xFF.
1111110a 10aaaaaa 10bbbbbb 10bbcccc 10ccccdd 10dddddd

, where small letters stand for "payload" bits of bytes a..d, highestmost has only 7 bits

comp.lang.tcl 2008-04:
Newsgroups: comp.lang.tcl
From: r_haer...@gmx.de
Date: Sat, 26 Apr 2008 11:55:45 -0700 (PDT)
Local: Sat, Apr 26 2008 2:55 pm 
Subject: unicode - get character representation from \uxxx notation

to show my problem see the following example: 

> set tcl_patchLevel 

> set str "n\u00E4mlich" 

> set c 0xE4 
> set str "n\\u[format %04.4X $ch]mlich" 

How do I get the \u00E4 in the character representation let's say 
iso8859-1 ? 

> encoding convertto iso8859-1 $str 

Newsgroups: comp.lang.tcl
From: billpo...@alum.mit.edu
Date: Sat, 26 Apr 2008 14:21:27 -0700 (PDT)
Local: Sat, Apr 26 2008 5:21 pm 
Subject: Re: unicode - get character representation from \uxxx notation

To convert the hex number expressed as a string 0x00e4 to a Unicode 
character, use: 

format "%c" 0x00e4 

You can then use encoding convertto to convert this to another 
encoding, e.g.: 

encoding convertto iso8859-1 [format "%c" 0x00e4]

LV 2008-07-08:

I've a request from a developer concerning whether Tcl is capable of handling characters larger than the Unicode BMP. His application was using tdom and it encountered the 𝒜 character, which is a script-A, unicode value 0x1D49C, which tdom reports it can't handle because it is limited to UTF-8 chars up to 3 bytes in length.

What do Tcl programmers do to properly process the longer characters?

Note this is in an enterprise setting. Finding a solution is critical in the publishing (web or print) arena.

RS 2008-07-09: Unicode out of BMP (> U+FFFF) requires a deeper rework of Tcl and Tk: we'd need 32 bit chars and/or surrogate pairs. UTF-8 at least can deal with 31-bit Unicodes by principle.

LV During July, 2008, there was some discussion in the TCT mailing list [1] (let's see how long that URL lasts...) about ways that the Tcl code itself could evolve to handle things better. But for right now, users have to face either dealing with their wide unicode via a different programming language in some way (whether converting wide characters to some other similar character, using some sort of macro representation, etc.)

AMG, 2015: It's been seven years since the above discussion. What progress has been made?

tcl.h contains the comment:
"Tcl is currently UCS-2 and planning UTF-16 for the Unicode string rep that Tcl_UniChar represents. Changing the size of Tcl_UniChar is not supported."

Fast random access to characters is quite important, e.g. for regular expressions, so I don't see how standard UTF-16 meets Tcl's needs unless augmented by some kind of indexing mechanism. Maybe the thought is reduced performance is acceptable for strings outside the BMP due to their assumed rarity, though I hope for logarithmic rather than linear, perhaps with some caching to further optimize the common situation of the sought-for character indexes being near each other.

But this is kind of a worst-of-both-worlds sort of deal. If you're going to have to pay for variable-width representation, might as well go with UTF-8 rather than -16.

AMG: How are combining characters handled? They seem to be treated as individual characters, and they're only combined in the display. Trouble with this is that the cursor can go between combining characters, along with similar problems like cutting a string in the middle of what's called a grapheme cluster.