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Diffstat (limited to 'doc/unigbrk.texi')
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diff --git a/doc/unigbrk.texi b/doc/unigbrk.texi index db4df6a..196bd9f 100644 --- a/doc/unigbrk.texi +++ b/doc/unigbrk.texi @@ -2,11 +2,18 @@ @chapter Grapheme cluster breaks in strings @code{<unigbrk.h>} @cindex grapheme cluster breaks +@cindex grapheme cluster boundaries @cindex breaks, grapheme cluster +@cindex boundaries, between grapheme clusters This include file declares functions for determining where in a string ``grapheme clusters'' start and end. A ``grapheme cluster'' is an approximation to a user-perceived character, which sometimes -corresponds to multiple Unicode characters. The letter @samp{@'e}, +corresponds to multiple Unicode characters. Editing operations such as +mouse selection, cursor movement, and backspacing often operate on +grapheme clusters as units, not on individual characters. + +Some grapheme clusters are built from a base character and a combining +character. The letter @samp{@'e}, for example, is most commonly represented in Unicode as a single character U+00E8 @sc{LATIN SMALL LETTER E WITH ACUTE}. It is, however, equally valid to use the pair of characters U+0065 @sc{LATIN @@ -14,6 +21,12 @@ SMALL LETTER E} followed by U+0301 @sc{COMBINING ACUTE ACCENT}. Since the user would perceive this pair of characters as a single character, they would be grouped into a single grapheme cluster. +But there are also grapheme clusters that consist of several base characters. +For example, a Devanagari letter and a Devanagari vowel sign that follows it +may form a grapheme cluster. Similarly, some pairs of Thai characters and +Hangul syllables (formed by two or three Hangul characters) are grapheme +clusters. + @menu * Grapheme cluster breaks in a string:: * Grapheme cluster break property:: @@ -65,10 +78,11 @@ grapheme cluster break at start of text. @node Grapheme cluster break property @section Grapheme cluster break property -This is a more low-level API. The grapheme cluster break property is a property defined -in Unicode Standard Annex #29, section ``Grapheme Cluster Boundaries, see -@url{http://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries}.@texnl{} It is -used for determining the grapheme cluster breaks in a string. +This is a more low-level API. The grapheme cluster break property is a +property defined in Unicode Standard Annex #29, section ``Grapheme Cluster +Boundaries'', see +@url{http://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries}.@texnl{} +It is used for determining the grapheme cluster breaks in a string. The following are the possible values of the grapheme cluster break property. More values may be added in the future. @@ -87,7 +101,8 @@ property. More values may be added in the future. @deftypevrx Constant int GBP_LVT @end deftypevr -The following function looks up the grapheme cluster break property of a character. +The following function looks up the grapheme cluster break property of a +character. @deftypefun int uc_graphemeclusterbreak_property (ucs4_t @var{uc}) Returns the Grapheme_Cluster_Break property of a Unicode character. @@ -102,7 +117,7 @@ Returns true if there is an grapheme cluster boundary between Unicode characters @var{a} and @var{b}. There is always a grapheme cluster break at the start or end of text. -Specify zero for @var{a} or @var{b} to indicate start of text or end +You can specify zero for @var{a} or @var{b} to indicate start of text or end of text, respectively. This implements the extended (not legacy) grapheme cluster rules |