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A '''Unicode block''' is an interval of code points which represent characters that are semantically related to each other. For example, there is a Unicode block for characters from the Devanagari script which is used by several Indian languages. Another Unicode block corresponds to characters which denote mathematical operators, such as those that indicate the union and the intersection of sets.

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'' is an organisational unit , ftp://www.unicode.org/Public/UNIDATA/Blocks.txt, Retrieved 2017-11-03.</ref> of the Unicode code spaceCharacter 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 official list main properties of blocks are described in the blocks is available [ftp:Unicode Standard<ref name="Unicode"//www> (Section 3.4, paragraph D10b).unicode Every block is an interval of code points, and distinct blocks are disjoint from each other.org/Public/UNIDATA/BlocksIn particular, the blocks form a partition of a subset of the Unicode code space.txt  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 Unicode Web site]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.

Every The Unicode Standard gives every block is an interval a unique name that describes the common semantic nature of its code points. Different blocks These names are disjoint from each othercase insensitive, and every code point belongs to at least one blockthe hyphens, spaces, and underscores, in them are insignificant. ThusFor example, one can refer to the blocks form a partition of the set of all block whose Unicode name is {{code|Myanmar Extended-A}} as {{code|myanmarextendeda}}, {{code|MyanmarExtendedA}}, or {{code points|myanmar_extended_a}}. The number ConTeXt chooses the first of these alternative styles for the names of code points in a block varies. Some have just 16 code pointsblocks, and some others have thousands of code pointsas described below.

A code block starts at a code point that is a multiple of 16. The number of code points in each a block is also a multiple of 16varies. ThusSome, such as the hexadecimal representation of the first block named {{code|Syriac Supplement}}, have just 16 code point in a block is of the form ''pqrs''0points, and that of some others, such as the last block named {{code point in it is |CJK Unified Ideographs Extension B}} with 42720 elements, have thousands of the form ''tuvw''F, where ''p'', ''q'', ''r'', ''s'', ''t'', ''u'', and ''v'', are hexadecimal digitscode points.

The Unicode standard gives every Every assigned code point belongs to some block a unique name that describes the common semantic nature of its , but there are blocks which contain unassigned code points. These names are case insensitive, and the hyphens, spaces, and underscores, in them are insignificant. For too; for example, one can refer to the block whose Unicode name is named {{code|Myanmar Extended-ATelugu}} as {{contains the unassigned code|myanmarextendeda}}point 0C50. On the other hand, {{there are some code|MyanmarExtendedA}}points, necessarily unassigned, or {{which do not belong to any block; the code|myanmar_extended_a}}point 0870 is one such. ConTeXt chooses Thus, the first set of all assigned code points is a proper subset of these alternative styles for the names union of all the blocks, as described belowand the union of all the blocks is a proper subset of the Unicode code space.

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 article entitled [[List of Unicode blocks ==]] contains a table of Unicode blocks, their ConTeXt names, and links to more information about them.

See the article [[List == An example usage of Unicode blocks]] for a table of Unicode blocks, their in ConTeXt names, and links to more information about them.==

== Usage A typical use of Unicode blocks is in the blocks 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.

A typical use of Unicode blocks is For example, in the definition of '''fallback''' fonts to provide following document, the base font [[TeX Gyre - Old Content|TeX Gyre Pagella]] does not have the glyphs for certain Cyrillic characters. Sometimes, when writing a document in ConTeXt, one needs to typeset special symbols that whose code points are not available in the base font of the documentUnicode block {{code|Cyrillic}}. In such a situation, one can specify a fallback font The document uses the {{cmd|definefallbackfamily}} command to provide these missing symbols. Another use of fallback fonts arises when one wants to replace get the glyphs for some characters in this block from the base font with glyphs for those characters from another {{code|DejaVu Serif}} font. In such a case, The ConTeXt name of the latter font can be specified block is supplied as a fallback fontthe value of the key {{code|range}} in the last setup of the command.

<context source=yestext="Here is an image showing the relevant part of the PDF file obtained by running context on a file containing this document:">\definefallbackfamily [mainface] [serifrm] [DejaVu Serif] [range=cyrillic,force=yes]

\definefontfamily [mainface] [serifrm] [TeX Gyre Pagella]

\rightaligned{--- — Lewis Caroll, Jabberwocky} 

\rightaligned {--- — Дина Григорьевна Орловская, Бармаглот}