ntextWordBreak(n)				 ntext Word Boundary Detection for the Text Widget				 ntextWordBreak(n)

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NAME

       ntextWordBreak - ntext Word Boundary Detection for the Text Widget

SYNOPSIS

       package require Tcl  8.5

       package require Tk  8.5

       package require ntext  ?0.81?

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DESCRIPTION

       The ntext package provides a binding tag named Ntext for use by text widgets in place of the default Text binding tag.

       Navigation and selection in a text widget require the detection of words and their boundaries.  The word boundary detection facilities pro-
       vided by Tcl/Tk through the Text binding tag are limited because they define only one class of "word" characters and  one  class  of  "non-
       word"  characters.  The Ntext binding tag uses more general rules for word boundary detection, that define two classes of "word" characters
       and one class of "non-word" characters.

CONFIGURATION OPTIONS

       The behaviour of Ntext may be configured application-wide by setting the values of a number of namespace variables.  One of these is  rele-
       vant to word boundary detection:

       ::ntext::classicWordBreak

       o      0  -  (default  value)  selects Ntext behaviour, i.e. platform-independent, two classes of word characters and one class of non-word
	      characters.

       o      1 - selects classic Text behaviour, i.e. platform-dependent, one class of word characters and one class of non-word characters

       o      After changing this value, Ntext 's regexp matching patterns should be recalculated.  See FUNCTIONS for details and advanced config-
	      uration options.

ADVANCED USE

VARIABLES (ADVANCED USE)
       ::ntext::tcl_match_wordBreakAfter

       ::ntext::tcl_match_wordBreakBefore

       ::ntext::tcl_match_endOfWord

       ::ntext::tcl_match_startOfNextWord

       ::ntext::tcl_match_startOfPreviousWord

       These  variables  hold  the regexp patterns that are used by Ntext to search for word boundaries.  If they are changed, subsequent searches
       are immediately altered.  In many situations, it it unnecessary to alter the values of these variables directly: instead call  one  of  the
       functions ::ntext::initializeMatchPatterns, ::ntext::createMatchPatterns.

       In  the Text binding tag one can change the search rules by changing the values of the global variables tcl_wordchars and tcl_nonwordchars.
       The equivalent operation in the Ntext binding tag is to call ::ntext::createMatchPatterns with appropriate arguments.

FUNCTIONS (ADVANCED USE)
       If a simple regexp search should prove insufficient, the following functions (analogous to the Tcl/Tk core's tcl_wordBreakAfter etc) may be
       replaced by the developer:

       ntext::new_wordBreakAfter

       ntext::new_wordBreakBefore

       ntext::new_endOfWord

       ntext::new_startOfNextWord

       ntext::new_startOfPreviousWord

FUNCTIONS

       Each  function calculates the five regexp search patterns that define the word boundary searches.  These values are stored in the namespace
       variables listed above.

       ::ntext::initializeMatchPatterns

       o      This function is called when Ntext is first used, and needs to be called again only if  the  script  changes  the  value	of  either
	      ::ntext::classicWordBreak  or  ::tcl_platform(platform).	 The  function is called with no arguments.  It is useful when the desired
	      search patterns are the default patterns for either the Ntext or Text binding tag, and so are implicitly specified by the values	of
	      ::ntext::classicWordBreak and ::tcl_platform(platform) alone.

       ::ntext::createMatchPatterns new_nonwordchars new_word1chars ?new_word2chars?

       o      This  function is useful in a wider range of situations than ::ntext::initializeMatchPatterns.  It calculates the regexp search pat-
	      terns for any case with one class of "non-word" characters and one or two classes of "word" characters.

	      Each argument should be a regexp expression defining a class of characters.  An argument will usually be a bracket  expression,  but
	      might alternatively be a class-shorthand escape, or a single character.  The third argument may be omitted, or supplied as the empty
	      string, in which case it is unused.

	      The first argument is interpreted as the class of non-word characters; the second argument (and the third, if present)  are  classes
	      of  word characters.  The classes should include all possible characters and will normally be mutually exclusive: it is often conve-
	      nient to define one class as the negation of the other two.

WORD BOUNDARY MATCHING

       The problem of word boundary selection is a vexed one, because text is used to represent a universe of different types of information,  and
       there are no simple rules that are useful for all data types or for all purposes.

       Ntext  attempts	to improve on the facilities available in classic Text by providing facilities for more complex definitions of words (with
       three classes of characters instead of two).

       What is a word?	Why two classes of word?

       When using the modified cursor keys <Control-Left> and <Control-Right> to navigate through a Ntext widget, the  cursor  is  placed  at  the
       start of a word.  A word is defined as a sequence of one or more characters from only one of the two defined "word" classes; it may be pre-
       ceded by a character from the other "word" class or from the "non-word" class.

       The double-click of mouse button 1 selects a word of text, where in this case a "word" may be as defined above, or alternatively may  be  a
       sequence of one or more characters from the "non-word" class of characters.

       Traditionally  Tcl has defined only one word class and one non-word class: on Windows, the non-word class is whitespace, and so alphanumer-
       ics and punctuation belong to the same class.  On other platforms, punctuation is bundled with whitespace  as  "non-word"  characters.	In
       either case, the navigation and selection of text are unnecessarily coarse-grained, and sometimes give unhelpful results.

       The  use  of  three  classes  of characters might make selection too fine-grained; but in this case, holding down the Shift key and double-
       clicking another word is an excellent way to select a longer range of text (a useful binding that Tcl/Tk has long  provided  but  which	is
       missing in other systems).

       As  well  as  its defaults, Ntext permits the developer to define their own classes of characters, or to revert to the classic Text defini-
       tions, or to specify their own regexp matching patterns.

EXAMPLE

       To use Ntext with Tcl/Tk's usual word-boundary detection rules:

       package require ntext
       text .t
       bindtags .t {.t Ntext . all}
       set ::ntext::classicWordBreak 1
       ::ntext::initializeMatchPatterns

       See bindtags for more information.

       To define a different set of word-boundary detection rules:

       package require ntext
       text .t
       bindtags .t {.t Ntext . all}
       ::ntext::createMatchPatterns 
	 {[[:space:][:cntrl:]]} {[[:punct:]]} {[^[:punct:][:space:][:cntrl:]]}

       See regexp, re_syntax for more information.

SEE ALSO

       bindtags, ntext, re_syntax, regexp, text

KEYWORDS

       bindtags, re_syntax, regexp, text

ntext								       0.81							 ntextWordBreak(n)