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Unicode blocks in ConTeXt (view source)
Revision as of 16:09, 4 November 2017
, 16:09, 4 November 2017no edit summary
ConTeXt has special names for all Unicode blocks. These names can be used to specify ranges of code points in the setups of several commands.
This article uses some basic terms, such as ''character'', ''code point'', and ''assigned code point'', from the Unicode Standard<ref name="Unicode">The Unicode Consortium, ''The Unicode Standard'', Version 10.0.0, The Unicode Consortium, Mountain View, CA, USA, 2016, http://www.unicode.org/versions/Unicode10.0.0/, Retrieved 2017-11-03.</ref>. For brief descriptions of these terms, see the Unicode glossary<ref name="Unicode-glossary">The Unicode Consortium, ''Glossary'', http://www.unicode.org/glossary/, Retrieved 2017-11-03.</ref>.
== Unicode blocks ==
A Unicode block, or, simply, a block, is any of the subsets of the Unicode code space that are listed in the file {{code|Blocks.txt}}<ref name="Blocks">The Unicode Consortium, ''Blocks.txt'', ftp://www.unicode.org/Public/UNIDATA/Blocks.txt, Retrieved 2017-11-03.</ref> of the Unicode Character Database. The Unicode code space is the set of all code points, that is, the set of all integers from 0 to the integer whose hexadecimal representation is 10FFF.
The main properties of blocks are described in the Unicode Standard<ref>The name="Unicode Consortium, ''The Unicode Standard'', Version 10.0.0, The Unicode Consortium, Mountain View, CA, USA, 2016, http://www.unicode.org/versions/Unicode10.0.0/, Retrieved 2017-11-03.<"/ref> (Section 3.4, paragraph D10b). Every block is an interval of code points, and distinct blocks are disjoint from each other. In particular, the blocks form a partition of a subset of the Unicode code space.
A block starts at a code point that is a multiple of 16. The number of code points in each block is also a multiple of 16. Thus, the hexadecimal representation of the first code point in a block is of the form ''pqrs''0, and that of the last code point in it is of the form ''tuvw''F, where ''p'', ''q'', ''r'', ''s'', ''t'', ''u'', ''v'', and ''w'', are hexadecimal digits.
The number of code points in a block varies. Some, such as the block named {{code|Syriac Supplement}}, have just 16 code points, and some others, such as the block named {{code|CJK Unified Ideographs Extension B}} with 42720 elements, have thousands of code points.
Every assigned code point belongs to some block, but there are blocks which contain unassigned code points too; for example, the block named {{code|Telugu}} contains the unassigned code point 0C50. LastlyOn the other hand, there are some code points, necessarily unassigned, which do not belong to any block; the code point 0870 is one such. Thus, the set of all assigned code points is a proper subset of the union of all the blocks, and the union of all the blocks is a proper subset of the Unicode code space.
== ConTeXt names of Unicode blocks ==
ConTeXt has its own names for all the Unicode blocks. These names are defined in the source file {{src|char-ini.lua}}. Most of them are obtained by converting the Unicode name of the block to the lower case, and removing the hyphens and spaces in the name. == The list of blocks == See the article entitled [[List of Unicode blocks]], for contains a table of Unicode blocks, their ConTeXt names, and links to more information about them.
== An example usage of Unicode blocks in ConTeXt ==
A typical use of Unicode blocks is in the definition of '''fallback''' fonts to provide glyphs for certain characters. Sometimes, when writing a document in ConTeXt, one needs to typeset special symbols that are not available in the base font of the document. In such a situation, one can specify a fallback font to provide these missing symbols.
For example, in the following document, containing verses from the Wikipedia article on ''Jabberwocky''<ref>Wikipedia contributors, ''Jabberwocky'', Wikipedia: The Free Encyclopaedia, 2017-11-03, 07:58 UTC, https://en.wikipedia.org/w/index.php?title=Jabberwocky&oldid=808507152, Retrieved 2017-11-03.</ref>, the base font [[TeX Gyre|TeX Gyre Pagella]] does not have the glyphs for Cyrillic characters, whose code points are in the Unicode block {{code|Cyrillic}}. The document uses the {{cmd|definefallbackfamily}} command to get the glyphs for this block from the {{code|DejaVu Serif}} font. The ConTeXt name of the block is supplied as the value of the key {{code|range}} in the last setup of the command.
<context source=yes text="Here is an image showing the relevant part of the PDF file obtained by running context on a file containing this document:">
\stoptext
</context>
The verses in the above example are from the Wikipedia article on the poem ''Jabberwocky''<ref>Wikipedia contributors, ''Jabberwocky'', Wikipedia: The Free Encyclopaedia, 2017-11-03, 07:58 UTC, https://en.wikipedia.org/w/index.php?title=Jabberwocky&oldid=808507152, Retrieved 2017-11-03.</ref> by Lewis Carroll.
== Another example ==
so {{code|context}} is indeed, and as expected, taking some of the glyphs from the fallback font, which, in this case, is provided by the local operating system.
== See also ==
* [[List of Unicode blocks]]
* {{cmd|definefontfallback}} — manual page with more information on the ConTeXt names of blocks, and their usage.
* {{src|char-ini.lua}} — source file containing the definitions of the ConTeXt names of Unicode blocks.
== References ==
<references/>
