| Unicode::LineBreak(3pm) | User Contributed Perl Documentation | Unicode::LineBreak(3pm) |
Unicode::LineBreak - UAX #14 Unicode Line Breaking Algorithm
use Unicode::LineBreak;
$lb = Unicode::LineBreak->new();
$broken = $lb->break($string);
Unicode::LineBreak performs Line Breaking Algorithm described in Unicode Standard Annex #14 [UAX #14]. East_Asian_Width informative property defined by Annex #11 [UAX #11] will be concerned to determine breaking positions.
Following terms are used for convenience.
Mandatory break is obligatory line breaking behavior defined by core rules and performed regardless of surrounding characters. Arbitrary break is line breaking behavior allowed by core rules and chosen by user to perform it. Arbitrary break includes direct break and indirect break defined by [UAX #14].
Alphabetic characters are characters usually no line breaks are allowed between pairs of them, except that other characters provide break oppotunities. Ideographic characters are characters that usually allow line breaks both before and after themselves. [UAX #14] classifies most of alphabetic to AL and most of ideographic to ID (These terms are inaccurate from the point of view by grammatology). On several scripts, breaking positions are not obvious by each characters therefore heuristic based on dictionary is used.
Number of columns of a string is not always equal to the number of characters it contains: Each of characters is either wide, narrow or nonspacing; they occupy 2, 1 or 0 columns, respectively. Several characters may be both wide and narrow by the contexts they are used. Characters may have more various widths by customization.
Note: This method gives just approximate description of line breaking behavior. Use break() and so on to wrap actual texts.
"new" and "config" methods accept following pairs. Some of them affect number of columns ([E]), grapheme cluster segmentation ([G]) (see also Unicode::GCString) or line breaking behavior ([L]).
Note: This option was introduced at release 1.011.
See also "Urgent" option and "User-Defined Breaking Behaviors".
In "EASTASIAN" context, characters with East_Asian_Width property ambiguous (A) are treated as "wide" and with Line Breaking Class AI as ideographic (ID).
In "NONEASTASIAN" context, characters with East_Asian_Width property ambiguous (A) are treated as "narrow" and with Line Breaking Class AI as alphabetic (AL).
By default, no tailorings are available. See also "Tailoring Character Properties".
By default, no tailorings are available. See also "Tailoring Character Properties".
See also "ColMax", "ColMin" and "EAWidth" options.
Note: This "nonspacing" value is extension by this module, not a part of [UAX #11].
Note: Property value CP was introduced by Unicode 5.2.0. Property values HL and CJ were introduced by Unicode 6.1.0. Property value RI was introduced by Unicode 6.2.0.
N.B.: Current release supports Thai script of modern Thai language only.
If you specify subroutine reference as a value of "Format" option, it should accept three arguments:
$MODIFIED = &subroutine(SELF, EVENT, STR);
SELF is a Unicode::LineBreak object, EVENT is a string to determine the context that subroutine was called in, and STR is a fragment of Unicode string leading or trailing breaking position.
EVENT |When Fired |Value of STR
-----------------------------------------------------------------
"sot" |Beginning of text |Fragment of first line
"sop" |After mandatory break|Fragment of next line
"sol" |After arbitrary break|Fragment on sequel of line
"" |Just before any |Complete line without trailing
|breaks |SPACEs
"eol" |Arbitrary break |SPACEs leading breaking position
"eop" |Mandatory break |Newline and its leading SPACEs
"eot" |End of text |SPACEs (and newline) at end of
| |text
-----------------------------------------------------------------
Subroutine should return modified text fragment or may return "undef" to express that no modification occurred. Note that modification in the context of "sot", "sop" or "sol" may affect decision of successive breaking positions while in the others won't.
Note: String arguments are actually sequences of grapheme clusters. See Unicode::GCString.
For example, following code folds lines removing trailing spaces:
sub fmt {
if ($_[1] =~ /^eo/) {
return "\n";
}
return undef;
}
my $lb = Unicode::LineBreak->new(Format => \&fmt);
$output = $lb->break($text);
When a line generated by arbitrary break is expected to be beyond measure of either CharMax, ColMax or ColMin, urgent break may be performed on successive string. If you specify subroutine reference as a value of "Urgent" option, it should accept two arguments:
@BROKEN = &subroutine(SELF, STR);
SELF is a Unicode::LineBreak object and STR is a Unicode string to be broken.
Subroutine should return an array of broken string STR.
Note: String argument is actually a sequence of grapheme clusters. See Unicode::GCString.
For example, following code inserts hyphen to the name of several chemical substances (such as Titin) so that it may be folded:
sub hyphenize {
return map {$_ =~ s/yl$/yl-/; $_} split /(\w+?yl(?=\w))/, $_[1];
}
my $lb = Unicode::LineBreak->new(Urgent => \&hyphenize);
$output = $lb->break("Methionylthreonylthreonylglutaminylarginyl...");
If you specify [REGEX, SUBREF] array reference as any of "Prep" option, subroutine should accept two arguments:
@BROKEN = &subroutine(SELF, STR);
SELF is a Unicode::LineBreak object and STR is a Unicode string matched with REGEX.
Subroutine should return an array of broken string STR.
For example, following code will break HTTP URLs using [CMOS] rule.
my $url = qr{http://[\x21-\x7E]+}i;
sub breakurl {
my $self = shift;
my $str = shift;
return split m{(?<=[/]) (?=[^/]) |
(?<=[^-.]) (?=[-~.,_?\#%=&]) |
(?<=[=&]) (?=.)}x, $str;
}
my $lb = Unicode::LineBreak->new(Prep => [$url, \&breakurl]);
$output = $lb->break($string);
Preserving State
Unicode::LineBreak object can behave as hash reference. Any items may be preserved throughout its life.
For example, following code will separate paragraphs with empty lines.
sub paraformat {
my $self = shift;
my $action = shift;
my $str = shift;
if ($action eq 'sot' or $action eq 'sop') {
$self->{'line'} = '';
} elsif ($action eq '') {
$self->{'line'} = $str;
} elsif ($action eq 'eol') {
return "\n";
} elsif ($action eq 'eop') {
if (length $self->{'line'}) {
return "\n\n";
} else {
return "\n";
}
} elsif ($action eq 'eot') {
return "\n";
}
return undef;
}
my $lb = Unicode::LineBreak->new(Format => \¶format);
$output = $lb->break($string);
If you specify subroutine reference as a value of "Sizing" option, it will be called with five arguments:
$COLS = &subroutine(SELF, LEN, PRE, SPC, STR);
SELF is a Unicode::LineBreak object, LEN is size of preceding string, PRE is preceding Unicode string, SPC is additional SPACEs and STR is a Unicode string to be processed.
Subroutine should return calculated number of columns of "PRE.SPC.STR". The number of columns may not be an integer: Unit of the number may be freely chosen, however, it should be same as those of "ColMin" and "ColMax" option.
Note: String arguments are actually sequences of grapheme clusters. See Unicode::GCString.
For example, following code processes lines with tab stops by each eight columns.
sub tabbedsizing {
my ($self, $cols, $pre, $spc, $str) = @_;
my $spcstr = $spc.$str;
while ($spcstr->lbc == LB_SP) {
my $c = $spcstr->item(0);
if ($c eq "\t") {
$cols += 8 - $cols % 8;
} else {
$cols += $c->columns;
}
$spcstr = $spcstr->substr(1);
}
$cols += $spcstr->columns;
return $cols;
};
my $lb = Unicode::LineBreak->new(LBClass => [ord("\t") => LB_SP],
Sizing => \&tabbedsizing);
$output = $lb->break($string);
Character properties may be tailored by "LBClass" and "EAWidth" options. Some constants are defined for convenience of tailoring.
Line Breaking Properties
Non-starters of Kana-like Characters
By default, several hiragana, katakana and characters corresponding to kana are treated as non-starters (NS or CJ). When the following pair(s) are specified for value of "LBClass" option, these characters are treated as normal ideographic characters (ID).
N.B. Some of them are neither hiragana nor katakana.
Hiragana or katakana prolonged sound marks: U+30FC KATAKANA-HIRAGANA PROLONGED SOUND MARK and U+FF70 HALFWIDTH KATAKANA-HIRAGANA PROLONGED SOUND MARK.
N.B. These letters are optionally treated either as non-starter or as normal ideographic. See [JIS X 4051] 6.1.1, [JLREQ] 3.1.7 or [UAX14].
N.B. U+3095, U+3096, U+30F5, U+30F6 are considered to be neither hiragana nor katakana.
N.B. Although this character is not kana, it is usually regarded as abbreviation to sequence of hiragana ま す or katakana マ ス, MA and SU.
N.B. This character is classified as non-starter (NS) by [UAX #14] and as the class corresponding to ID by [JIS X 4051] and [JLREQ].
Ambiguous Quotation Marks
By default, some punctuations are ambiguous quotation marks (QU).
Danish, Finnish, Norwegian and Swedish use 9-style or right-pointing punctuations (’ ” » ›) as both opening and closing quotation marks.
IDEOGRAPHIC SPACE
East_Asian_Width Properties
Some particular letters of Latin, Greek and Cyrillic scripts have ambiguous (A) East_Asian_Width property. Thus, these characters are treated as wide in "EASTASIAN" context. Specifying "EAWidth => [ AMBIGUOUS_"*"() => EA_N ]", those characters are always treated as narrow.
On the other hand, despite several characters were occasionally rendered as wide characters by number of implementations for East Asian character sets, they are given narrow (Na) East_Asian_Width property just because they have fullwidth (F) compatibility characters. Specifying "EAWidth" as below, those characters are treated as ambiguous --- wide on "EASTASIAN" context.
Built-in defaults of option parameters for "new" and "config" method can be overridden by configuration files: Unicode/LineBreak/Defaults.pm. For more details read Unicode/LineBreak/Defaults.pm.sample.
Please report bugs or buggy behaviors to developer.
CPAN Request Tracker: <http://rt.cpan.org/Public/Dist/Display.html?Name=Unicode-LineBreak>.
Consult $VERSION variable.
Character properties this module is based on are defined by Unicode Standard version 8.0.0.
This module is intended to implement UAX14-C2.
Ranges | UAX #14 | UAX #11 | Description
-------------------------------------------------------------
U+20A0..U+20CF | PR [*1] | N [*2] | Currency symbols
U+3400..U+4DBF | ID | W | CJK ideographs
U+4E00..U+9FFF | ID | W | CJK ideographs
U+D800..U+DFFF | AL (SG) | N | Surrogates
U+E000..U+F8FF | AL (XX) | F or N (A) | Private use
U+F900..U+FAFF | ID | W | CJK ideographs
U+20000..U+2FFFD | ID | W | CJK ideographs
U+30000..U+3FFFD | ID | W | Old hanzi
U+F0000..U+FFFFD | AL (XX) | F or N (A) | Private use
U+100000..U+10FFFD | AL (XX) | F or N (A) | Private use
Other unassigned | AL (XX) | N | Unassigned,
| | | reserved or
| | | noncharacters
-------------------------------------------------------------
[*1] Except U+20A7 PESETA SIGN (PO),
U+20B6 LIVRE TOURNOIS SIGN (PO), U+20BB NORDIC MARK SIGN (PO)
and U+20BE LARI SIGN (PO).
[*2] Except U+20A9 WON SIGN (H) and U+20AC EURO SIGN
(F or N (A)).
Text::LineFold, Text::Wrap, Unicode::GCString.
Copyright (C) 2009-2018 Hatuka*nezumi - IKEDA Soji <hatuka(at)nezumi.nu>.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| 2025-01-23 | perl v5.40.0 |