JezK

Edit File: LineBreak.pod

=encoding utf-8

=head1 NAME

Unicode::LineBreak - UAX #14 Unicode Line Breaking Algorithm

=head1 SYNOPSIS

use Unicode::LineBreak;
    $lb = Unicode::LineBreak->new();
    $broken = $lb->break($string);

=head1 DESCRIPTION

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.

=head2 Terminology

Following terms are used for convenience.

B<Mandatory break> is obligatory line breaking behavior defined by core
rules and performed regardless of surrounding characters.
B<Arbitrary break> is line breaking behavior allowed by core rules
and chosen by user to perform it.
Arbitrary break includes B<direct break> and B<indirect break>
defined by [UAX #14].

B<Alphabetic characters> are characters usually no line breaks are allowed
between pairs of them, except that other characters provide break
oppotunities.
B<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.

B<Number of columns> of a string is not always equal to the number of characters it contains:
Each of characters is either B<wide>, B<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.

=head1 PUBLIC INTERFACE

=head2 Line Breaking

=over 4

=item new ([KEY => VALUE, ...])

I<Constructor>.
About KEY => VALUE pairs see L</Options>.

=item break (STRING)

I<Instance method>.
Break Unicode string STRING and returns it.
In array context, returns array of lines contained in the result.

=item break_partial (STRING)

I<Instance method>.
Same as break() but accepts incremental inputs.
Give C<undef> as STRING argument to specify that input was completed.

=item config (KEY)

=item config (KEY => VALUE, ...)

I<Instance method>.
Get or update configuration.  About KEY => VALUE pairs see L</Options>.

=item copy

I<Copy constructor>.
Create a copy of object instance.

=begin comment

=item reset

I<Undocumented>.

=end comment

=back

=head2 Getting Informations

=over 4

=item breakingRule (BEFORESTR, AFTERSTR)

I<Instance method>.
Get possible line breaking behavior between strings BEFORESTR and AFTERSTR.
See L</Constants> for returned value.

B<Note>:
This method gives just approximate description of line breaking behavior.
Use break() and so on to wrap actual texts.

=item context ([Charset => CHARSET], [Language => LANGUAGE])

I<Function>.
Get language/region context used by character set CHARSET or
language LANGUAGE.

=back

=begin comment

=head3 Methods Planned to be Deprecated

=over 4

=item lbrule (BEFORE, AFTER)

I<Instance method>.
Get possible line breaking behavior between class BEFORE and class AFTER.
See L</Constants> for returned value.

B<Note>:
This method gives just approximate description of line breaking behavior.
Use break() and so on to wrap actual texts.

B<Note>:
Use breakingRule().

=item strsize (LEN, PRE, SPC, STR)

I<Instance method>.
Calculate I<number of columns> of Unicode string
PRE.SPC.STR based on character widths defined by [UAX #11].

B<Note>:
Use L<Unicode::GCString/columns>.

=back

=end comment

=head2 Options

L</new> and L</config> methods accept following pairs.
Some of them affect number of columns ([B<E>]),
grapheme cluster segmentation ([B<G>])
(see also L<Unicode::GCString>) or
line breaking behavior ([B<L>]).

=over 4

=item BreakIndent => C<"YES"> | C<"NO">

[B<L>]
Always allows break after SPACEs at beginning of line, a.k.a. indent.
[UAX #14] does not take account of such usage of SPACE.
Default is C<"YES">.

B<Note>:
This option was introduced at release 1.011.

=item CharMax => NUMBER

[B<L>]
Possible maximum number of characters in one line,
not counting trailing SPACEs and newline sequence.
Note that number of characters generally doesn't represent length of line.
Default is C<998>.
C<0> means unlimited (as of release 2012.01).

=item ColMin => NUMBER

[B<L>]
Minimum number of columns which line broken arbitrarily may include, not
counting trailing spaces and newline sequences.
Default is C<0>.

=item ColMax => NUMBER

[B<L>]
Maximum number of columns line may include not counting trailing spaces and
newline sequence.  In other words, maximum length of line.
Default is C<76>.

=back

See also L</Urgent> option and L</User-Defined Breaking Behaviors>.

=over 4

=item ComplexBreaking => C<"YES"> | C<"NO">

[B<L>]
Performs heuristic breaking on South East Asian complex context.
Default is, if word segmentation for South East Asian writing systems is
enabled, C<"YES">.

=item Context => CONTEXT

[B<E>][B<L>]
Specify language/region context.
Currently available contexts are C<"EASTASIAN"> and C<"NONEASTASIAN">.
Default context is C<"NONEASTASIAN">.

In C<"EASTASIAN"> context, characters with East_Asian_Width property
ambiguous (A) are treated as "wide" and with Line Breaking Class AI as
ideographic (ID).

In C<"NONEASTASIAN"> context, characters with East_Asian_Width property
ambiguous (A) are treated as "narrow" and with Line Breaking Class AI as
alphabetic (AL).

=item EAWidth => C<[> ORD C<=E<gt>> PROPERTY C<]>

=item EAWidth => C<undef>

[B<E>]
Tailor classification of East_Asian_Width property.
ORD is UCS scalar value of character or array reference of them.
PROPERTY is one of East_Asian_Width property values
and extended values
(See L</Constants>).
This option may be specified multiple times.
If C<undef> is specified, all tailoring assigned before will be canceled.

By default, no tailorings are available.
See also L</Tailoring Character Properties>.

=item Format => METHOD

[B<L>]
Specify the method to format broken lines.

=over 4

=item C<"SIMPLE">

Default method.
Just only insert newline at arbitrary breaking positions.

=item C<"NEWLINE">

Insert or replace newline sequences with that specified by L</Newline> option,
remove SPACEs leading newline sequences or end-of-text.  Then append newline
at end of text if it does not exist.

=item C<"TRIM">

Insert newline at arbitrary breaking positions. Remove SPACEs leading
newline sequences.

=item C<undef>

Do nothing, even inserting any newlines.

=item Subroutine reference

See L</Formatting Lines>.

=back

=item HangulAsAL => C<"YES"> | C<"NO">

[B<L>]
Treat hangul syllables and conjoining jamos as alphabetic characters (AL).
Default is C<"NO">.

=item LBClass => C<[> ORD C<=E<gt>> CLASS C<]>

=item LBClass => C<undef>

[B<G>][B<L>]
Tailor classification of line breaking property.
ORD is UCS scalar value of character or array reference of them.
CLASS is one of line breaking classes (See L</Constants>).
This option may be specified multiple times.
If C<undef> is specified, all tailoring assigned before will be canceled.

By default, no tailorings are available.
See also L</Tailoring Character Properties>.

=item LegacyCM => C<"YES"> | C<"NO">

[B<G>][B<L>]
Treat combining characters lead by a SPACE as an isolated combining character
(ID).
As of Unicode 5.0, such use of SPACE is not recommended.
Default is C<"YES">.

=item Newline => STRING

[B<L>]
Unicode string to be used for newline sequence.
Default is C<"\n">.

=item Prep => METHOD

[B<L>]
Add user-defined line breaking behavior(s).
This option may be specified multiple times.
Following methods are available.

=over 4

=item C<"NONBREAKURI">

Won't break URIs.

=item C<"BREAKURI">

Break URIs according to a rule suitable for printed materials.
For more details see [CMOS], sections 6.17 and 17.11.

=item C<[> REGEX, SUBREF C<]>

The sequences matching regular expression REGEX will be broken by
subroutine referred by SUBREF.
For more details see L</User-Defined Breaking Behaviors>.

=item C<undef>

Cancel all methods assigned before.

=back

=item Sizing => METHOD

[B<L>]
Specify method to calculate size of string.
Following options are available.

=over 4

=item C<"UAX11">

Default method.
Sizes are computed by columns of each characters according to built-in
character database.

=item C<undef>

Number of grapheme clusters (see L<Unicode::GCString>) contained in the string.

=item Subroutine reference

See L</Calculating String Size>.

=back

See also L</ColMax>, L</ColMin> and L</EAWidth> options.

=item Urgent => METHOD

[B<L>]
Specify method to handle excessing lines.
Following options are available.

=over 4

=item C<"CROAK">

Print error message and die.

=item C<"FORCE">

Force breaking excessing fragment.

=item C<undef>

Default method.
Won't break excessing fragment.

=item Subroutine reference

See L</User-Defined Breaking Behaviors>.

=back

=item ViramaAsJoiner => C<"YES"> | C<"NO">

[B<G>]
Virama sign ("halant" in Hindi, "coeng" in Khmer) and its succeeding letter
are not broken.
Default is C<"YES">.
B<Note>:
This option was introduced by release 2012.001_29.
On previous releases, it was fixed to C<"NO">.
"Default" grapheme cluster defined by [UAX #29] does not include this
feature.

=back

=begin comment

=head3 Obsoleted Options

=over 4

=item TailorEA => C<[> ORD C<=E<gt>> PROPERTY, ... C<]>

Obsoleted equivalent to L</EAWidth>.

=item TailorLB => C<[> ORD C<=E<gt>> CLASS, ... C<]>

Obsoleted equivalent to L</LBClass>.

=item UserBreaking => C<[>METHOD, ...C<]>

Obsoleted equivalent to L</Prep>.

=back

=end comment

=head2 Constants

=over 4

=item C<EA_Na>, C<EA_N>, C<EA_A>, C<EA_W>, C<EA_H>, C<EA_F>

Index values to specify six East_Asian_Width property values defined by
[UAX #11]:
narrow (Na), neutral (N), ambiguous (A), wide (W), halfwidth (H) and
fullwidth (F).

=item C<EA_Z>

Index value to specify nonspacing characters.

B<Note>:
This "nonspacing" value is extension by this module,
not a part of [UAX #11].

=begin comment

C<EA_ZA> and C<EA_ZW>: Undocumented.

Earlier releases had only C<EA_Z>.
C<EA_ZA> and C<EA_ZW> were added by release 2012.10.

=end comment

=item C<LB_BK>, C<LB_CR>, C<LB_LF>, C<LB_NL>, C<LB_SP>, C<LB_OP>, C<LB_CL>, C<LB_CP>, C<LB_QU>, C<LB_GL>, C<LB_NS>, C<LB_EX>, C<LB_SY>, C<LB_IS>, C<LB_PR>, C<LB_PO>, C<LB_NU>, C<LB_AL>, C<LB_HL>, C<LB_ID>, C<LB_IN>, C<LB_HY>, C<LB_BA>, C<LB_BB>, C<LB_B2>, C<LB_CB>, C<LB_ZW>, C<LB_CM>, C<LB_WJ>, C<LB_H2>, C<LB_H3>, C<LB_JL>, C<LB_JV>, C<LB_JT>, C<LB_SG>, C<LB_AI>, C<LB_CJ>, C<LB_SA>, C<LB_XX>, C<LB_RI>

Index values to specify 40 line breaking property values (classes)
defined by [UAX #14].

B<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.

=item C<MANDATORY>, C<DIRECT>, C<INDIRECT>, C<PROHIBITED>

Four values to specify line breaking behaviors:
Mandatory break; Both direct break and indirect break are allowed;
Indirect break is allowed but direct break is prohibited;
Prohibited break.

=item C<Unicode::LineBreak::SouthEastAsian::supported>

Flag to determin if word segmentation for South East Asian writing systems is
enabled.
If this feature was enabled, a non-empty string is set. 
Otherwise, C<undef> is set.

B<N.B.>: Current release supports Thai script of modern Thai language only.

=item C<UNICODE_VERSION>

A string to specify version of Unicode standard this module refers.

=back

=head1 CUSTOMIZATION

=head2 Formatting Lines

If you specify subroutine reference as a value of L</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.

Subroutine should return modified text fragment or may return
C<undef> to express that no modification occurred.
Note that modification in the context of C<"sot">, C<"sop"> or C<"sol"> may
affect decision of successive breaking positions while in the others won't.

B<Note>:
String arguments are actually sequences of grapheme clusters.
See L<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);

=head2 User-Defined Breaking Behaviors

When a line generated by arbitrary break is expected to be beyond measure of
either CharMax, ColMax or ColMin, B<urgent break> may be
performed on successive string.
If you specify subroutine reference as a value of L</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.

B<Note>:
String argument is actually a sequence of grapheme clusters.
See L<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 L</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);

=head3 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 => \&paraformat);
    $output = $lb->break($string);

=head2 Calculating String Size

If you specify subroutine reference as a value of L</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 C<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 L</ColMin> and L</ColMax> option.

B<Note>:
String arguments are actually sequences of grapheme clusters.
See L<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);

=head2 Tailoring Character Properties

Character properties may be tailored by L</LBClass> and L</EAWidth>
options.  Some constants are defined for convenience of tailoring.

=head3 Line Breaking Properties

=head4 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 L</LBClass> option,
these characters are treated as normal ideographic characters (ID).

=over 4

=item C<KANA_NONSTARTERS() =E<gt> LB_ID>

All of characters below.

=item C<IDEOGRAPHIC_ITERATION_MARKS() =E<gt> LB_ID>

Ideographic iteration marks.
U+3005 IDEOGRAPHIC ITERATION MARK, U+303B VERTICAL IDEOGRAPHIC ITERATION MARK, U+309D HIRAGANA ITERATION MARK, U+309E HIRAGANA VOICED ITERATION MARK, U+30FD KATAKANA ITERATION MARK and U+30FE KATAKANA VOICED ITERATION MARK.

N.B. Some of them are neither hiragana nor katakana.

=item C<KANA_SMALL_LETTERS() =E<gt> LB_ID>

=item C<KANA_PROLONGED_SOUND_MARKS() =E<gt> LB_ID>

Hiragana or katakana small letters:
Hiragana small letters U+3041 A, U+3043 I, U+3045 U, U+3047 E, U+3049 O, U+3063 TU, U+3083 YA, U+3085 YU, U+3087 YO, U+308E WA, U+3095 KA, U+3096 KE. 
Katakana small letters U+30A1 A, U+30A3 I, U+30A5 U, U+30A7 E, U+30A9 O, U+30C3 TU, U+30E3 YA, U+30E5 YU, U+30E7 YO, U+30EE WA, U+30F5 KA, U+30F6 KE.
Katakana phonetic extensions U+31F0 KU - U+31FF RO.
Halfwidth katakana small letters U+FF67 A - U+FF6F TU.

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.

=item C<MASU_MARK() =E<gt> LB_ID>

U+303C MASU MARK.

N.B. Although this character is not kana, it is usually regarded as
abbreviation to sequence of hiragana E<0x307E> E<0x3059> or
katakana E<0x30DE> E<0x30B9>, 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].

=back

=head4 Ambiguous Quotation Marks

By default, some punctuations are ambiguous quotation marks (QU).

=over 4

=item C<BACKWARD_QUOTES() =E<gt> LB_OP, FORWARD_QUOTES() =E<gt> LB_CL>

Some languages (Dutch, English, Italian, Portuguese, Spanish, Turkish and
most East Asian) use rotated-9-style punctuations (E<0x2018> E<0x201C>) as
opening and 9-style punctuations (E<0x2019> E<0x201D>) as closing quotation
marks.

=item C<FORWARD_QUOTES() =E<gt> LB_OP, BACKWARD_QUOTES() =E<gt> LB_CL>

Some others (Czech, German and Slovak) use 9-style punctuations
(E<0x2019> E<0x201D>) as opening and rotated-9-style punctuations
(E<0x2018> E<0x201C>) as closing quotation marks.

=item C<BACKWARD_GUILLEMETS() =E<gt> LB_OP, FORWARD_GUILLEMETS() =E<gt> LB_CL>

French, Greek, Russian etc. use left-pointing guillemets (E<0x00AB> E<0x2039>)
as opening and right-pointing guillemets (E<0x00BB> E<0x203A>) as closing
quotation marks.

=item C<FORWARD_GUILLEMETS() =E<gt> LB_OP, BACKWARD_GUILLEMETS() =E<gt> LB_CL>

German and Slovak use right-pointing guillemets (E<0x00BB> E<0x203A>) as
opening and left-pointing guillemets (E<0x00AB> E<0x2039>) as closing
quotation marks.

=back

Danish, Finnish, Norwegian and Swedish use 9-style or right-pointing
punctuations (E<0x2019> E<0x201D> E<0x00BB> E<0x203A>) as both opening and
closing quotation marks.

=head4 IDEOGRAPHIC SPACE

=over 4

=item C<IDEOGRAPHIC_SPACE() =E<gt> LB_BA>

U+3000 IDEOGRAPHIC SPACE won't be placed at beginning of line.
This is default behavior.

=item C<IDEOGRAPHIC_SPACE() =E<gt> LB_ID>

IDEOGRAPHIC SPACE can be placed at beginning of line.
This was default behavior by Unicode 6.2 and earlier.

=item C<IDEOGRAPHIC_SPACE() =E<gt> LB_SP>

IDEOGRAPHIC SPACE won't be placed at beginning of line,
and will protrude from end of line.

=back

=head3 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 C<"EASTASIAN"> context.
Specifying C<EAWidth =E<gt> [ AMBIGUOUS_>*C<() =E<gt> EA_N ]>,
those characters are always treated as narrow.

=over 4

=item C<AMBIGUOUS_ALPHABETICS() =E<gt> EA_N>

Treat all of characters below as East_Asian_Width neutral (N).

=item C<AMBIGUOUS_CYRILLIC() =E<gt> EA_N>

=item C<AMBIGUOUS_GREEK() =E<gt> EA_N>

=item C<AMBIGUOUS_LATIN() =E<gt> EA_N>

Treate letters having ambiguous (A) width of Cyrillic, Greek and Latin scripts
as neutral (N).

=back

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 C<EAWidth> as below, those characters are treated as ambiguous
--- wide on C<"EASTASIAN"> context.

=over 4

=item C<QUESTIONABLE_NARROW_SIGNS() =E<gt> EA_A>

U+00A2 CENT SIGN, U+00A3 POUND SIGN, U+00A5 YEN SIGN (or yuan sign),
U+00A6 BROKEN BAR, U+00AC NOT SIGN, U+00AF MACRON.

=back

=head2 Configuration File

Built-in defaults of option parameters for L</new> and L</config> method
can be overridden by configuration files:
F<Unicode/LineBreak/Defaults.pm>.
For more details read F<Unicode/LineBreak/Defaults.pm.sample>.

=head1 BUGS

Please report bugs or buggy behaviors to developer.

CPAN Request Tracker:
L<http://rt.cpan.org/Public/Dist/Display.html?Name=Unicode-LineBreak>.

=head1 VERSION

Consult $VERSION variable.

=head2 Incompatible Changes

=over 4

=item Release 2012.06

=over 4

=item *

eawidth() method was deprecated.
L<Unicode::GCString/columns> may be used instead.

=item *

lbclass() method was deprecated.
Use L<Unicode::GCString/lbc> or L<Unicode::GCString/lbcext>.

=back

=head2 Conformance to Standards

Character properties this module is based on are defined by
Unicode Standard version 8.0.0.

This module is intended to implement UAX14-C2.

=head1 IMPLEMENTATION NOTES

=over 4

=item *

Some ideographic characters may be treated either as NS or as ID by choice.

=item *

Hangul syllables and conjoining jamos may be treated as
either ID or AL by choice.

=item *

Characters assigned to AI may be resolved to either AL or ID by choice.

=item *

Character(s) assigned to CB are not resolved.

=item *

Characters assigned to CJ are always resolved to NS.
More flexible tailoring mechanism is provided.

=item *

When word segmentation for South East Asian writing systems is not supported,
characters assigned to SA are resolved to AL,
except that characters that have Grapheme_Cluster_Break property value
Extend or SpacingMark be resolved to CM.

=item *

Characters assigned to SG or XX are resolved to AL.

=item *

Code points of following UCS ranges are given fixed property values even
if they have not been assigned any characters.

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)).

=item *

Characters belonging to General Category Mn, Me, Cc, Cf, Zl or Zp are
treated as nonspacing by this module.

=back

=head1 REFERENCES

=over 4

=item [CMOS]

I<The Chicago Manual of Style>, 15th edition.
University of Chicago Press, 2003.

=item [JIS X 4051]

JIS X 4051:2004
I<日本語文書の組版方法> (I<Formatting Rules for Japanese Documents>).
Japanese Standards Association, 2004.

=item [JLREQ]

Anan, Yasuhiro et al.
I<Requirements for Japanese Text Layout>,
W3C Working Group Note 3 April 2012.
L<http://www.w3.org/TR/2012/NOTE-jlreq-20120403/>.

=begin comment

=item [Kubota]

Kubota, Tomohiro (2001-2002).
Width problems, "I<Problems on Interoperativity between Unicode and CJK Local Encodings>".
L<http://web.archive.org/web/people.debian.org/~kubota/unicode-symbols-width2.html>.

=end comment

=item [UAX #11]

A. Freytag (ed.) (2008-2009).
I<Unicode Standard Annex #11: East Asian Width>, Revisions 17-19.
L<http://unicode.org/reports/tr11/>.

=item [UAX #14]

A. Freytag and A. Heninger (eds.) (2008-2015).
I<Unicode Standard Annex #14: Unicode Line Breaking Algorithm>, Revisions 22-35.
L<http://unicode.org/reports/tr14/>.

=item [UAX #29]

Mark Davis (ed.) (2009-2013).
I<Unicode Standard Annex #29: Unicode Text Segmentation>, Revisions 15-23.
L<http://www.unicode.org/reports/tr29/>.

=back

=head1 SEE ALSO

L<Text::LineFold>, L<Text::Wrap>, L<Unicode::GCString>.

=head1 AUTHOR

This program is free software; you can redistribute it and/or modify it 
under the same terms as Perl itself.

=cut

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