ntextWordBreak(ntext Word Boundary Detection for the Text WidntextWordBreak(n)______________________________________________________________________________NAMEntextWordBreak - ntext Word Boundary Detection for the Text Widget
SYNOPSIS
package require Tcl 8.5
package require Tk 8.5
package require ntext ?0.81?
_________________________________________________________________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
provided 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
· 0 - (default value) selects Ntext behaviour, i.e. platform-inde‐
pendent, two classes of word characters and one class of non-
word characters.
· 1 - selects classic Text behaviour, i.e. platform-dependent, one
class of word characters and one class of non-word characters
· After changing this value, Ntext 's regexp matching patterns
should be recalculated. See FUNCTIONS for details and advanced
configuration options.
ADVANCED USEVARIABLES (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::createMatchPat‐
terns.
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::cre‐
ateMatchPatterns 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
· 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(plat‐
form) alone.
::ntext::createMatchPatterns new_nonwordchars new_word1chars
?new_word2chars?
· This function is useful in a wider range of situations than
::ntext::initializeMatchPatterns. It calculates the regexp
search patterns for any case with one class of "non-word" char‐
acters 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 char‐
acters; the second argument (and the third, if present) are
classes of word characters. The classes should include all pos‐
sible characters and will normally be mutually exclusive: it is
often convenient 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 preceded 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 charac‐
ters.
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-click‐
ing 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)
