src/third_party/icu/source/data/brkitr/line.txt - cobalt - Git at Google

 # Copyright (c) 2002-2015  International Business Machines Corporation and
 # others. All Rights Reserved.
 #
 #  file:  line.txt
 #
 #         Line Breaking Rules
 #         Implement default line breaking as defined by
 #         Unicode Standard Annex #14 Revision 34 for Unicode 8.0
 #         http://www.unicode.org/reports/tr14/
 #
 #         TODO:  Rule LB 8 remains as it was in Unicode 5.2
 #         This is only because of a limitation of ICU break engine implementation,
 #         not because the older behavior is desirable.
 #
 #         This corresponds to CSS line-break=strict (BCP47 -u-lb-strict).
 #         It sets characters of class CJ to behave like NS.

 #
 #  Character Classes defined by TR 14.
 #

 !!chain;
 !!LBCMNoChain;


 !!lookAheadHardBreak;
 #
 #  !!lookAheadHardBreak    Described here because it is (as yet) undocumented elsewhere
 #                          and only used for the line break rules.
 #
 #           It is used in the implementation of rule LB 10
 #           which says to treat any combining mark that is not attached to a base
 #           character as if it were of class AL  (alphabetic).
 #
 #           The problem occurs in the reverse rules.
 #
 #           Consider a sequence like, with correct breaks as shown
 #               LF  ID  CM  AL  AL
 #                  ^       ^       ^
 #           Then consider the sequence without the initial ID (ideographic)
 #                 LF  CM  AL  AL
 #                    ^           ^
 #           Our CM, which in the first example was attached to the ideograph,
 #           is now unattached, becomes an alpha, and joins in with the other
 #           alphas.
 #
 #           When iterating forwards, these sequences do not present any problems
 #           When iterating backwards, we need to look ahead when encountering
 #           a CM to see whether it attaches to something further on or not.
 #           (Look-ahead in a reverse rule is looking towards the start)
 #
 #           If the CM is unattached, we need to force a break.
 #
 #           !!lookAheadHardBreak forces the run time state machine to
 #           stop immediately when a look ahead rule ( '/' operator) matches,
 #           and set the match position to that of the look-ahead operator,
 #           no matter what other rules may be in play at the time.
 #
 #           See rule LB 19 for an example.
 #

 $AI = [:LineBreak =  Ambiguous:];
 $AL = [:LineBreak =  Alphabetic:];
 $BA = [:LineBreak =  Break_After:];
 $BB = [:LineBreak =  Break_Before:];
 $BK = [:LineBreak =  Mandatory_Break:];
 $B2 = [:LineBreak =  Break_Both:];
 $CB = [:LineBreak =  Contingent_Break:];
 $CJ = [:LineBreak =  Conditional_Japanese_Starter:];
 $CL = [:LineBreak =  Close_Punctuation:];
 $CM = [:LineBreak =  Combining_Mark:];
 $CP = [:LineBreak =  Close_Parenthesis:];
 $CR = [:LineBreak =  Carriage_Return:];
 $EX = [:LineBreak =  Exclamation:];
 $GL = [:LineBreak =  Glue:];
 $HL = [:LineBreak =  Hebrew_Letter:];
 $HY = [:LineBreak =  Hyphen:];
 $H2 = [:LineBreak =  H2:];
 $H3 = [:LineBreak =  H3:];
 $ID = [:LineBreak =  Ideographic:];
 $IN = [:LineBreak =  Inseperable:];
 $IS = [:LineBreak =  Infix_Numeric:];
 $JL = [:LineBreak =  JL:];
 $JV = [:LineBreak =  JV:];
 $JT = [:LineBreak =  JT:];
 $LF = [:LineBreak =  Line_Feed:];
 $NL = [:LineBreak =  Next_Line:];
 $NS = [[:LineBreak =  Nonstarter:] $CJ];
 $NU = [:LineBreak =  Numeric:];
 $OP = [:LineBreak =  Open_Punctuation:];
 $PO = [:LineBreak =  Postfix_Numeric:];
 $PR = [:LineBreak =  Prefix_Numeric:];
 $QU = [:LineBreak =  Quotation:];
 $RI = [:LineBreak =  Regional_Indicator:];
 $SA = [:LineBreak =  Complex_Context:];
 $SG = [:LineBreak =  Surrogate:];
 $SP = [:LineBreak =  Space:];
 $SY = [:LineBreak =  Break_Symbols:];
 $WJ = [:LineBreak =  Word_Joiner:];
 $XX = [:LineBreak =  Unknown:];
 $ZW = [:LineBreak =  ZWSpace:];

 #   Dictionary character set, for triggering language-based break engines. Currently
 #   limited to LineBreak=Complex_Context. Note that this set only works in Unicode
 #   5.0 or later as the definition of Complex_Context was corrected to include all
 #   characters requiring dictionary break.

 $dictionary = [:LineBreak = Complex_Context:];

 #
 #  Rule LB1.  By default, treat AI  (characters with ambiguous east Asian width),
 #                               SA  (South East Asian: Thai, Lao, Khmer)
 #                               SG  (Unpaired Surrogates)
 #                               XX  (Unknown, unassigned)
 #                         as $AL  (Alphabetic)
 #
 $ALPlus = [$AL $AI $SA $SG $XX];

 #
 #  Combining Marks.   X $CM*  behaves as if it were X.  Rule LB6.
 #
 $ALcm = $ALPlus $CM*;
 $BAcm = $BA $CM*;
 $BBcm = $BB $CM*;
 $B2cm = $B2 $CM*;
 $CLcm = $CL $CM*;
 $CPcm = $CP $CM*;
 $EXcm = $EX $CM*;
 $GLcm = $GL $CM*;
 $HLcm = $HL $CM*;
 $HYcm = $HY $CM*;
 $H2cm = $H2 $CM*;
 $H3cm = $H3 $CM*;
 $IDcm = $ID $CM*;
 $INcm = $IN $CM*;
 $IScm = $IS $CM*;
 $JLcm = $JL $CM*;
 $JVcm = $JV $CM*;
 $JTcm = $JT $CM*;
 $NScm = $NS $CM*;
 $NUcm = $NU $CM*;
 $OPcm = $OP $CM*;
 $POcm = $PO $CM*;
 $PRcm = $PR $CM*;
 $QUcm = $QU $CM*;
 $RIcm = $RI $CM*;
 $SYcm = $SY $CM*;
 $WJcm = $WJ $CM*;

 ## -------------------------------------------------

 !!forward;

 #
 #  Each class of character can stand by itself as an unbroken token, with trailing combining stuff
 #
 $ALPlus $CM+;
 $BA $CM+;
 $BB $CM+;
 $B2 $CM+;
 $CL $CM+;
 $CP $CM+;
 $EX $CM+;
 $GL $CM+;
 $HL $CM+;
 $HY $CM+;
 $H2 $CM+;
 $H3 $CM+;
 $ID $CM+;
 $IN $CM+;
 $IS $CM+;
 $JL $CM+;
 $JV $CM+;
 $JT $CM+;
 $NS $CM+;
 $NU $CM+;
 $OP $CM+;
 $PO $CM+;
 $PR $CM+;
 $QU $CM+;
 $RI $CM+;
 $SY $CM+;
 $WJ $CM+;

 #
 # CAN_CM  is the set of characters that may combine with CM combining chars.
 #         Note that Linebreak UAX 14's concept of a combining char and the rules
 #         for what they can combine with are _very_ different from the rest of Unicode.
 #
 #         Note that $CM itself is left out of this set.  If CM is needed as a base
 #         it must be listed separately in the rule.
 #
 $CAN_CM  = [^$SP $BK $CR $LF $NL $ZW $CM];       # Bases that can   take CMs
 $CANT_CM = [ $SP $BK $CR $LF $NL $ZW $CM];       # Bases that can't take CMs

 #
 # AL_FOLLOW  set of chars that can unconditionally follow an AL
 #            Needed in rules where stand-alone $CM s are treated as AL.
 #            Chaining is disabled with CM because it causes other failures,
 #            so for this one case we need to manually list out longer sequences.
 #
 $AL_FOLLOW_NOCM = [$BK $CR $LF $NL $ZW $SP];
 $AL_FOLLOW_CM   = [$CL $CP $EX $HL $IS $SY $WJ $GL $OP $QU $BA $HY $NS $IN $NU $ALPlus];
 $AL_FOLLOW      = [$AL_FOLLOW_NOCM $AL_FOLLOW_CM];


 #
 #  Rule LB 4, 5    Mandatory (Hard) breaks.
 #
 $LB4Breaks    = [$BK $CR $LF $NL];
 $LB4NonBreaks = [^$BK $CR $LF $NL];
 $CR $LF {100};

 #
 #  LB 6    Do not break before hard line breaks.
 #
 $LB4NonBreaks?  $LB4Breaks {100};    # LB 5  do not break before hard breaks.
 $CAN_CM $CM*    $LB4Breaks {100};
 $CM+            $LB4Breaks {100};

 # LB 7         x SP
 #              x ZW
 $LB4NonBreaks [$SP $ZW];
 $CAN_CM $CM*  [$SP $ZW];
 $CM+          [$SP $ZW];

 #
 # LB 8         Break after zero width space
 #              TODO:  ZW SP* <break>
 #              An engine change is required to write the reverse rule for this.
 #              For now, leave the Unicode 5.2 rule, ZW <break>
 #
 $LB8Breaks    = [$LB4Breaks $ZW];
 $LB8NonBreaks = [[$LB4NonBreaks] - [$ZW]];


 # LB 9     Combining marks.      X   $CM needs to behave like X, where X is not $SP, $BK $CR $LF $NL
 #                                $CM not covered by the above needs to behave like $AL
 #                                See definition of $CAN_CM.

 $CAN_CM $CM+;                   #  Stick together any combining sequences that don't match other rules.
 $CM+;

 #
 # LB 11  Do not break before or after WORD JOINER & related characters.
 #
 $CAN_CM $CM*  $WJcm;
 $LB8NonBreaks $WJcm;
 $CM+          $WJcm;

 $WJcm $CANT_CM;
 $WJcm $CAN_CM $CM*;

 #
 # LB 12  Do not break after NBSP and related characters.
 #         GL  x
 #
 $GLcm $CAN_CM $CM*;
 $GLcm $CANT_CM;

 #
 # LB 12a  Do not break before NBSP and related characters ...
 #            [^SP BA HY] x GL
 #
 [[$LB8NonBreaks] - [$SP $BA $HY]] $CM* $GLcm;
 $CM+ GLcm;


 #
 # LB 13   Don't break before ']' or '!' or ';' or '/', even after spaces.
 #
 $LB8NonBreaks $CL;
 $CAN_CM $CM*  $CL;
 $CM+          $CL;              # by rule 10, stand-alone CM behaves as AL

 $LB8NonBreaks $CP;
 $CAN_CM $CM*  $CP;
 $CM+          $CP;              # by rule 10, stand-alone CM behaves as AL

 $LB8NonBreaks $EX;
 $CAN_CM $CM*  $EX;
 $CM+          $EX;              # by rule 10, stand-alone CM behaves as AL

 $LB8NonBreaks $IS;
 $CAN_CM $CM*  $IS;
 $CM+          $IS;              # by rule 10, stand-alone CM behaves as AL

 $LB8NonBreaks $SY;
 $CAN_CM $CM*  $SY;
 $CM+          $SY;              # by rule 10, stand-alone CM behaves as AL


 #
 # LB 14  Do not break after OP, even after spaces
 #
 $OPcm $SP* $CAN_CM $CM*;
 $OPcm $SP* $CANT_CM;

 $OPcm $SP+ $CM+ $AL_FOLLOW?;    # by rule 10, stand-alone CM behaves as AL

 # LB 15
 $QUcm $SP* $OPcm;

 # LB 16
 ($CLcm | $CPcm) $SP* $NScm;

 # LB 17
 $B2cm $SP* $B2cm;

 #
 # LB 18  Break after spaces.
 #
 $LB18NonBreaks = [$LB8NonBreaks - [$SP]];
 $LB18Breaks    = [$LB8Breaks $SP];


 # LB 19
 #         x QU
 $LB18NonBreaks $CM* $QUcm;
 $CM+                $QUcm;

 #         QU  x
 $QUcm .?;
 $QUcm $LB18NonBreaks $CM*;    # Don't let a combining mark go onto $CR, $BK, etc.
                               #  TODO:  I don't think this rule is needed.


 # LB 20
 #        <break>  $CB
 #        $CB   <break>

 $LB20NonBreaks = [$LB18NonBreaks - $CB];

 # LB 21        x   (BA | HY | NS)
 #           BB x
 #
 $LB20NonBreaks $CM* ($BAcm | $HYcm | $NScm);

 $BBcm [^$CB];                                  #  $BB  x
 $BBcm $LB20NonBreaks $CM*;

 # LB 21a Don't break after Hebrew + Hyphen
 #   HL (HY | BA) x
 #
 $HLcm ($HYcm | $BAcm) [^$CB]?;

 # LB 21b (forward) Don't break between SY and HL
 # (break between HL and SY already disallowed by LB 13 above)
 $SYcm $HLcm;

 # LB 22
 ($ALcm | $HLcm) $INcm;
 $CM+     $INcm;     #  by rule 10, any otherwise unattached CM behaves as AL
 $EXcm    $INcm;
 $IDcm    $INcm;
 $INcm    $INcm;
 $NUcm    $INcm;


 # $LB 23
 $IDcm  $POcm;
 $ALcm  $NUcm;       # includes $LB19
 $HLcm  $NUcm;
 $CM+   $NUcm;       # Rule 10, any otherwise unattached CM behaves as AL
 $NUcm  $ALcm;
 $NUcm  $HLcm;

 #
 # LB 24
 #
 $PRcm $IDcm;
 $PRcm ($ALcm | $HLcm);
 $POcm ($ALcm | $HLcm);

 #
 # LB 25   Numbers.
 #
 ($PRcm | $POcm)? ($OPcm | $HYcm)? $NUcm ($NUcm | $SYcm | $IScm)* ($CLcm | $CPcm)? ($PRcm | $POcm)?;

 # LB 26  Do not break a Korean syllable
 #
 $JLcm ($JLcm | $JVcm | $H2cm | $H3cm);
 ($JVcm | $H2cm) ($JVcm | $JTcm);
 ($JTcm | $H3cm) $JTcm;

 # LB 27  Treat korean Syllable Block the same as ID  (don't break it)
 ($JLcm | $JVcm | $JTcm | $H2cm | $H3cm) $INcm;
 ($JLcm | $JVcm | $JTcm | $H2cm | $H3cm) $POcm;
 $PRcm ($JLcm | $JVcm | $JTcm | $H2cm | $H3cm);


 # LB 28   Do not break between alphabetics
 #
 ($ALcm | $HLcm) ($ALcm | $HLcm);
 $CM+ ($ALcm | $HLcm);      # The $CM+ is from rule 10, an unattached CM is treated as AL

 # LB 29
 $IScm ($ALcm | $HLcm);

 # LB 30
 ($ALcm | $HLcm | $NUcm) $OPcm;
 $CM+ $OPcm;         # The $CM+ is from rule 10, an unattached CM is treated as AL.
 $CPcm ($ALcm | $HLcm | $NUcm);

 # LB 30a  Do not break between regional indicators.
 $RIcm $RIcm;

 #
 #  Reverse Rules.
 #
 ## -------------------------------------------------

 !!reverse;

 $CM+ $ALPlus;
 $CM+ $BA;
 $CM+ $BB;
 $CM+ $B2;
 $CM+ $CL;
 $CM+ $CP;
 $CM+ $EX;
 $CM+ $GL;
 $CM+ $HL;
 $CM+ $HY;
 $CM+ $H2;
 $CM+ $H3;
 $CM+ $ID;
 $CM+ $IN;
 $CM+ $IS;
 $CM+ $JL;
 $CM+ $JV;
 $CM+ $JT;
 $CM+ $NS;
 $CM+ $NU;
 $CM+ $OP;
 $CM+ $PO;
 $CM+ $PR;
 $CM+ $QU;
 $CM+ $RI;
 $CM+ $SY;
 $CM+ $WJ;
 $CM+;


 #
 #  Sequences of the form  (shown forwards)
 #      [CANT_CM]  <break>  [CM]  [whatever]
 #  The CM needs to behave as an AL
 #
 $AL_FOLLOW $CM+ / (
           [$BK $CR $LF $NL $ZW {eof}] |
           $SP+ $CM+ $SP |
           $SP+ $CM* ([^$OP $CM $SP] | [$AL {eof}]));   # if LB 14 will match, need to surpress this break.
                                                #  LB14 says    OP SP* x .
                                                #    becomes    OP SP* x AL
                                                #    becomes    OP SP* x CM+ AL_FOLLOW
                                                #
                                                # Further note:  the $AL in [$AL {eof}] is only to work around
                                                #                a rule compiler bug which complains about
                                                #                empty sets otherwise.

 #
 #  Sequences of the form  (shown forwards)
 #      [CANT_CM]  <break> [CM]  <break>  [PR]
 #  The CM needs to behave as an AL
 #  This rule is concerned about getting the second of the two <breaks> in place.
 #

 [$PR   ] / $CM+ [$BK $CR $LF $NL $ZW $SP {eof}];


 # LB 4, 5, 5

 $LB4Breaks [$LB4NonBreaks-$CM];
 $LB4Breaks $CM+ $CAN_CM;
 $LF $CR;


 # LB 7         x SP
 #              x ZW
 [$SP $ZW] [$LB4NonBreaks-$CM];
 [$SP $ZW] $CM+ $CAN_CM;

 # LB 8 ZW SP* <break>
 #     TODO: to implement this, we need more than one look-ahead hard break in play at a time.
 #           Requires an engine enhancement.
 #   / $SP* $ZW

 # LB 9,10  Combining marks.
 #    X   $CM needs to behave like X, where X is not $SP or controls.
 #    $CM not covered by the above needs to behave like $AL
 # Stick together any combining sequences that don't match other rules.
 $CM+ $CAN_CM;


 # LB 11
 $CM* $WJ $CM* $CAN_CM;
 $CM* $WJ      [$LB8NonBreaks-$CM];

      $CANT_CM $CM* $WJ;
 $CM* $CAN_CM  $CM* $WJ;

 # LB 12a
 #      [^SP BA HY] x GL
 #
 $CM* $GL $CM* [$LB8NonBreaks-[$CM $SP $BA $HY]];

 # LB 12
 #     GL  x
 #
 $CANT_CM $CM* $GL;
 $CM* $CAN_CM $CM* $GL;


 # LB 13
 $CL $CM+ $CAN_CM;
 $CP $CM+ $CAN_CM;
 $EX $CM+ $CAN_CM;
 $IS $CM+ $CAN_CM;
 $SY $CM+ $CAN_CM;

 $CL [$LB8NonBreaks-$CM];
 $CP [$LB8NonBreaks-$CM];
 $EX [$LB8NonBreaks-$CM];
 $IS [$LB8NonBreaks-$CM];
 $SY [$LB8NonBreaks-$CM];

 # Rule 13 & 14 taken together for an edge case.
 #   Match this, shown forward
 #     OP SP+  ($CM+ behaving as $AL) (CL | CP | EX | IS | IY)
 #   This really wants to chain at the $CM+ (which is acting as an $AL)
 #   except for $CM chaining being disabled.
 [$CL $CP $EX $IS $SY] $CM+ $SP+ $CM* $OP;

 # LB 14    OP SP* x
 #
 $CM* $CAN_CM    $SP* $CM* $OP;
      $CANT_CM   $SP* $CM* $OP;
 $AL_FOLLOW? $CM+  $SP $SP* $CM* $OP;     #  by LB 10, behaves like $AL_FOLLOW? $AL $SP* $CM* $OP

      $AL_FOLLOW_NOCM $CM+ $SP+ $CM* $OP;
 $CM* $AL_FOLLOW_CM   $CM+ $SP+ $CM* $OP;
 $SY $CM $SP+ $OP;   # TODO:  Experiment.  Remove.


 # LB 15
 $CM* $OP $SP* $CM* $QU;

 # LB 16
 $CM* $NS $SP* $CM* ($CL | $CP);

 # LB 17
 $CM* $B2 $SP* $CM* $B2;

 # LB 18  break after spaces
 #        Nothing explicit needed here.


 #
 # LB 19
 #
 $CM* $QU $CM* $CAN_CM;                                #   . x QU
 $CM* $QU      $LB18NonBreaks;


 $CM* $CAN_CM  $CM* $QU;                               #   QU x .
      $CANT_CM $CM* $QU;

 #
 #  LB 20  Break before and after CB.
 #         nothing needed here.
 #

 # LB 21
 $CM* ($BA | $HY | $NS) $CM* [$LB20NonBreaks-$CM];     #  . x (BA | HY | NS)

 $CM* [$LB20NonBreaks-$CM] $CM* $BB;                   #  BB x .
 [^$CB] $CM* $BB;                                      #

 # LB21a
 [^$CB] $CM* ($HY | $BA) $CM* $HL;

 # LB21b (reverse)
 $CM* $HL $CM* $SY;

 # LB 22
 $CM* $IN $CM* ($ALPlus | $HL);
 $CM* $IN $CM* $EX;
 $CM* $IN $CM* $ID;
 $CM* $IN $CM* $IN;
 $CM* $IN $CM* $NU;

 # LB 23
 $CM* $PO $CM* $ID;
 $CM* $NU $CM* ($ALPlus | $HL);
 $CM* ($ALPlus | $HL) $CM* $NU;

 # LB 24
 $CM* $ID $CM* $PR;
 $CM* ($ALPlus | $HL) $CM* $PR;
 $CM* ($ALPlus | $HL) $CM* $PO;


 # LB 25
 ($CM* ($PR | $PO))? ($CM* ($CL | $CP))? ($CM* ($NU | $IS | $SY))* $CM* $NU ($CM* ($OP | $HY))? ($CM* ($PR | $PO))?;

 # LB 26
 $CM* ($H3 | $H2 | $JV | $JL) $CM* $JL;
 $CM* ($JT | $JV) $CM* ($H2 | $JV);
 $CM* $JT $CM* ($H3 | $JT);

 # LB 27
 $CM* $IN $CM* ($H3 | $H2 | $JT | $JV | $JL);
 $CM* $PO $CM* ($H3 | $H2 | $JT | $JV | $JL);
 $CM* ($H3 | $H2 | $JT | $JV | $JL) $CM* $PR;

 # LB 28
 $CM* ($ALPlus | $HL) $CM* ($ALPlus | $HL);


 # LB 29
 $CM* ($ALPlus | $HL) $CM* $IS;

 # LB 30
 $CM* $OP $CM* ($ALPlus | $HL | $NU);
 $CM* ($ALPlus | $HL | $NU) $CM* $CP;

 # LB 30a
 $CM* $RI $CM* $RI;

 ## -------------------------------------------------

 !!safe_reverse;

 # LB 9
 $CM+ [^$CM $BK $CR $LF $NL $ZW $SP];
 $CM+ $SP / .;

 # LB 14
 $SP+ $CM* $OP;

 # LB 15
 $SP+ $CM* $QU;

 # LB 16
 $SP+ $CM* ($CL | $CP);

 # LB 17
 $SP+ $CM* $B2;

 # LB 21
 $CM* ($HY | $BA) $CM* $HL;

 # LB 25
 ($CM* ($IS | $SY))+ $CM* $NU;
 ($CL | $CP) $CM* ($NU | $IS | $SY);

 # For dictionary-based break
 $dictionary $dictionary;

 ## -------------------------------------------------

 !!safe_forward;

 # Skip forward over all character classes that are involved in
 #   rules containing patterns with possibly more than one char
 #   of context.
 #
 #  It might be slightly more efficient to have specific rules
 #  instead of one generic one, but only if we could
 #  turn off rule chaining.  We don't want to move more
 #  than necessary.
 #
 [$CM $OP $QU $CL $CP $B2 $PR $HY $BA $SP $dictionary]+ [^$CM $OP $QU $CL $CP $B2 $PR $HY $BA $dictionary];
 $dictionary $dictionary;
	# Copyright (c) 2002-2015 International Business Machines Corporation and
	# others. All Rights Reserved.
	#
	# file: line.txt
	#
	# Line Breaking Rules
	# Implement default line breaking as defined by
	# Unicode Standard Annex #14 Revision 34 for Unicode 8.0
	# http://www.unicode.org/reports/tr14/
	#
	# TODO: Rule LB 8 remains as it was in Unicode 5.2
	# This is only because of a limitation of ICU break engine implementation,
	# not because the older behavior is desirable.
	#
	# This corresponds to CSS line-break=strict (BCP47 -u-lb-strict).
	# It sets characters of class CJ to behave like NS.

	#
	# Character Classes defined by TR 14.
	#

	!!chain;
	!!LBCMNoChain;


	!!lookAheadHardBreak;
	#
	# !!lookAheadHardBreak Described here because it is (as yet) undocumented elsewhere
	# and only used for the line break rules.
	#
	# It is used in the implementation of rule LB 10
	# which says to treat any combining mark that is not attached to a base
	# character as if it were of class AL (alphabetic).
	#
	# The problem occurs in the reverse rules.
	#
	# Consider a sequence like, with correct breaks as shown
	# LF ID CM AL AL
	# ^ ^ ^
	# Then consider the sequence without the initial ID (ideographic)
	# LF CM AL AL
	# ^ ^
	# Our CM, which in the first example was attached to the ideograph,
	# is now unattached, becomes an alpha, and joins in with the other
	# alphas.
	#
	# When iterating forwards, these sequences do not present any problems
	# When iterating backwards, we need to look ahead when encountering
	# a CM to see whether it attaches to something further on or not.
	# (Look-ahead in a reverse rule is looking towards the start)
	#
	# If the CM is unattached, we need to force a break.
	#
	# !!lookAheadHardBreak forces the run time state machine to
	# stop immediately when a look ahead rule ( '/' operator) matches,
	# and set the match position to that of the look-ahead operator,
	# no matter what other rules may be in play at the time.
	#
	# See rule LB 19 for an example.
	#

	$AI = [:LineBreak = Ambiguous:];
	$AL = [:LineBreak = Alphabetic:];
	$BA = [:LineBreak = Break_After:];
	$BB = [:LineBreak = Break_Before:];
	$BK = [:LineBreak = Mandatory_Break:];
	$B2 = [:LineBreak = Break_Both:];
	$CB = [:LineBreak = Contingent_Break:];
	$CJ = [:LineBreak = Conditional_Japanese_Starter:];
	$CL = [:LineBreak = Close_Punctuation:];
	$CM = [:LineBreak = Combining_Mark:];
	$CP = [:LineBreak = Close_Parenthesis:];
	$CR = [:LineBreak = Carriage_Return:];
	$EX = [:LineBreak = Exclamation:];
	$GL = [:LineBreak = Glue:];
	$HL = [:LineBreak = Hebrew_Letter:];
	$HY = [:LineBreak = Hyphen:];
	$H2 = [:LineBreak = H2:];
	$H3 = [:LineBreak = H3:];
	$ID = [:LineBreak = Ideographic:];
	$IN = [:LineBreak = Inseperable:];
	$IS = [:LineBreak = Infix_Numeric:];
	$JL = [:LineBreak = JL:];
	$JV = [:LineBreak = JV:];
	$JT = [:LineBreak = JT:];
	$LF = [:LineBreak = Line_Feed:];
	$NL = [:LineBreak = Next_Line:];
	$NS = [[:LineBreak = Nonstarter:] $CJ];
	$NU = [:LineBreak = Numeric:];
	$OP = [:LineBreak = Open_Punctuation:];
	$PO = [:LineBreak = Postfix_Numeric:];
	$PR = [:LineBreak = Prefix_Numeric:];
	$QU = [:LineBreak = Quotation:];
	$RI = [:LineBreak = Regional_Indicator:];
	$SA = [:LineBreak = Complex_Context:];
	$SG = [:LineBreak = Surrogate:];
	$SP = [:LineBreak = Space:];
	$SY = [:LineBreak = Break_Symbols:];
	$WJ = [:LineBreak = Word_Joiner:];
	$XX = [:LineBreak = Unknown:];
	$ZW = [:LineBreak = ZWSpace:];

	# Dictionary character set, for triggering language-based break engines. Currently
	# limited to LineBreak=Complex_Context. Note that this set only works in Unicode
	# 5.0 or later as the definition of Complex_Context was corrected to include all
	# characters requiring dictionary break.

	$dictionary = [:LineBreak = Complex_Context:];

	#
	# Rule LB1. By default, treat AI (characters with ambiguous east Asian width),
	# SA (South East Asian: Thai, Lao, Khmer)
	# SG (Unpaired Surrogates)
	# XX (Unknown, unassigned)
	# as $AL (Alphabetic)
	#
	$ALPlus = [$AL $AI $SA $SG $XX];

	#
	# Combining Marks. X $CM* behaves as if it were X. Rule LB6.
	#
	$ALcm = $ALPlus $CM*;
	$BAcm = $BA $CM*;
	$BBcm = $BB $CM*;
	$B2cm = $B2 $CM*;
	$CLcm = $CL $CM*;
	$CPcm = $CP $CM*;
	$EXcm = $EX $CM*;
	$GLcm = $GL $CM*;
	$HLcm = $HL $CM*;
	$HYcm = $HY $CM*;
	$H2cm = $H2 $CM*;
	$H3cm = $H3 $CM*;
	$IDcm = $ID $CM*;
	$INcm = $IN $CM*;
	$IScm = $IS $CM*;
	$JLcm = $JL $CM*;
	$JVcm = $JV $CM*;
	$JTcm = $JT $CM*;
	$NScm = $NS $CM*;
	$NUcm = $NU $CM*;
	$OPcm = $OP $CM*;
	$POcm = $PO $CM*;
	$PRcm = $PR $CM*;
	$QUcm = $QU $CM*;
	$RIcm = $RI $CM*;
	$SYcm = $SY $CM*;
	$WJcm = $WJ $CM*;

	## -------------------------------------------------

	!!forward;

	#
	# Each class of character can stand by itself as an unbroken token, with trailing combining stuff
	#
	$ALPlus $CM+;
	$BA $CM+;
	$BB $CM+;
	$B2 $CM+;
	$CL $CM+;
	$CP $CM+;
	$EX $CM+;
	$GL $CM+;
	$HL $CM+;
	$HY $CM+;
	$H2 $CM+;
	$H3 $CM+;
	$ID $CM+;
	$IN $CM+;
	$IS $CM+;
	$JL $CM+;
	$JV $CM+;
	$JT $CM+;
	$NS $CM+;
	$NU $CM+;
	$OP $CM+;
	$PO $CM+;
	$PR $CM+;
	$QU $CM+;
	$RI $CM+;
	$SY $CM+;
	$WJ $CM+;

	#
	# CAN_CM is the set of characters that may combine with CM combining chars.
	# Note that Linebreak UAX 14's concept of a combining char and the rules
	# for what they can combine with are _very_ different from the rest of Unicode.
	#
	# Note that $CM itself is left out of this set. If CM is needed as a base
	# it must be listed separately in the rule.
	#
	$CAN_CM = [^$SP $BK $CR $LF $NL $ZW $CM]; # Bases that can take CMs
	$CANT_CM = [ $SP $BK $CR $LF $NL $ZW $CM]; # Bases that can't take CMs

	#
	# AL_FOLLOW set of chars that can unconditionally follow an AL
	# Needed in rules where stand-alone $CM s are treated as AL.
	# Chaining is disabled with CM because it causes other failures,
	# so for this one case we need to manually list out longer sequences.
	#
	$AL_FOLLOW_NOCM = [$BK $CR $LF $NL $ZW $SP];
	$AL_FOLLOW_CM = [$CL $CP $EX $HL $IS $SY $WJ $GL $OP $QU $BA $HY $NS $IN $NU $ALPlus];
	$AL_FOLLOW = [$AL_FOLLOW_NOCM $AL_FOLLOW_CM];


	#
	# Rule LB 4, 5 Mandatory (Hard) breaks.
	#
	$LB4Breaks = [$BK $CR $LF $NL];
	$LB4NonBreaks = [^$BK $CR $LF $NL];
	$CR $LF {100};

	#
	# LB 6 Do not break before hard line breaks.
	#
	$LB4NonBreaks? $LB4Breaks {100}; # LB 5 do not break before hard breaks.
	$CAN_CM $CM* $LB4Breaks {100};
	$CM+ $LB4Breaks {100};

	# LB 7 x SP
	# x ZW
	$LB4NonBreaks [$SP $ZW];
	$CAN_CM $CM* [$SP $ZW];
	$CM+ [$SP $ZW];

	#
	# LB 8 Break after zero width space
	# TODO: ZW SP* <break>
	# An engine change is required to write the reverse rule for this.
	# For now, leave the Unicode 5.2 rule, ZW <break>
	#
	$LB8Breaks = [$LB4Breaks $ZW];
	$LB8NonBreaks = [[$LB4NonBreaks] - [$ZW]];


	# LB 9 Combining marks. X $CM needs to behave like X, where X is not $SP, $BK $CR $LF $NL
	# $CM not covered by the above needs to behave like $AL
	# See definition of $CAN_CM.

	$CAN_CM $CM+; # Stick together any combining sequences that don't match other rules.
	$CM+;

	#
	# LB 11 Do not break before or after WORD JOINER & related characters.
	#
	$CAN_CM $CM* $WJcm;
	$LB8NonBreaks $WJcm;
	$CM+ $WJcm;

	$WJcm $CANT_CM;
	$WJcm $CAN_CM $CM*;

	#
	# LB 12 Do not break after NBSP and related characters.
	# GL x
	#
	$GLcm $CAN_CM $CM*;
	$GLcm $CANT_CM;

	#
	# LB 12a Do not break before NBSP and related characters ...
	# [^SP BA HY] x GL
	#
	[[$LB8NonBreaks] - [$SP $BA $HY]] $CM* $GLcm;
	$CM+ GLcm;



	#
	# LB 13 Don't break before ']' or '!' or ';' or '/', even after spaces.
	#
	$LB8NonBreaks $CL;
	$CAN_CM $CM* $CL;
	$CM+ $CL; # by rule 10, stand-alone CM behaves as AL

	$LB8NonBreaks $CP;
	$CAN_CM $CM* $CP;
	$CM+ $CP; # by rule 10, stand-alone CM behaves as AL

	$LB8NonBreaks $EX;
	$CAN_CM $CM* $EX;
	$CM+ $EX; # by rule 10, stand-alone CM behaves as AL

	$LB8NonBreaks $IS;
	$CAN_CM $CM* $IS;
	$CM+ $IS; # by rule 10, stand-alone CM behaves as AL

	$LB8NonBreaks $SY;
	$CAN_CM $CM* $SY;
	$CM+ $SY; # by rule 10, stand-alone CM behaves as AL


	#
	# LB 14 Do not break after OP, even after spaces
	#
	$OPcm $SP* $CAN_CM $CM*;
	$OPcm $SP* $CANT_CM;

	$OPcm $SP+ $CM+ $AL_FOLLOW?; # by rule 10, stand-alone CM behaves as AL

	# LB 15
	$QUcm $SP* $OPcm;

	# LB 16
	($CLcm \| $CPcm) $SP* $NScm;

	# LB 17
	$B2cm $SP* $B2cm;

	#
	# LB 18 Break after spaces.
	#
	$LB18NonBreaks = [$LB8NonBreaks - [$SP]];
	$LB18Breaks = [$LB8Breaks $SP];


	# LB 19
	# x QU
	$LB18NonBreaks $CM* $QUcm;
	$CM+ $QUcm;

	# QU x
	$QUcm .?;
	$QUcm $LB18NonBreaks $CM*; # Don't let a combining mark go onto $CR, $BK, etc.
	# TODO: I don't think this rule is needed.


	# LB 20
	# <break> $CB
	# $CB <break>

	$LB20NonBreaks = [$LB18NonBreaks - $CB];

	# LB 21 x (BA \| HY \| NS)
	# BB x
	#
	$LB20NonBreaks $CM* ($BAcm \| $HYcm \| $NScm);

	$BBcm [^$CB]; # $BB x
	$BBcm $LB20NonBreaks $CM*;

	# LB 21a Don't break after Hebrew + Hyphen
	# HL (HY \| BA) x
	#
	$HLcm ($HYcm \| $BAcm) [^$CB]?;

	# LB 21b (forward) Don't break between SY and HL
	# (break between HL and SY already disallowed by LB 13 above)
	$SYcm $HLcm;

	# LB 22
	($ALcm \| $HLcm) $INcm;
	$CM+ $INcm; # by rule 10, any otherwise unattached CM behaves as AL
	$EXcm $INcm;
	$IDcm $INcm;
	$INcm $INcm;
	$NUcm $INcm;


	# $LB 23
	$IDcm $POcm;
	$ALcm $NUcm; # includes $LB19
	$HLcm $NUcm;
	$CM+ $NUcm; # Rule 10, any otherwise unattached CM behaves as AL
	$NUcm $ALcm;
	$NUcm $HLcm;

	#
	# LB 24
	#
	$PRcm $IDcm;
	$PRcm ($ALcm \| $HLcm);
	$POcm ($ALcm \| $HLcm);

	#
	# LB 25 Numbers.
	#
	($PRcm \| $POcm)? ($OPcm \| $HYcm)? $NUcm ($NUcm \| $SYcm \| $IScm)* ($CLcm \| $CPcm)? ($PRcm \| $POcm)?;

	# LB 26 Do not break a Korean syllable
	#
	$JLcm ($JLcm \| $JVcm \| $H2cm \| $H3cm);
	($JVcm \| $H2cm) ($JVcm \| $JTcm);
	($JTcm \| $H3cm) $JTcm;

	# LB 27 Treat korean Syllable Block the same as ID (don't break it)
	($JLcm \| $JVcm \| $JTcm \| $H2cm \| $H3cm) $INcm;
	($JLcm \| $JVcm \| $JTcm \| $H2cm \| $H3cm) $POcm;
	$PRcm ($JLcm \| $JVcm \| $JTcm \| $H2cm \| $H3cm);


	# LB 28 Do not break between alphabetics
	#
	($ALcm \| $HLcm) ($ALcm \| $HLcm);
	$CM+ ($ALcm \| $HLcm); # The $CM+ is from rule 10, an unattached CM is treated as AL

	# LB 29
	$IScm ($ALcm \| $HLcm);

	# LB 30
	($ALcm \| $HLcm \| $NUcm) $OPcm;
	$CM+ $OPcm; # The $CM+ is from rule 10, an unattached CM is treated as AL.
	$CPcm ($ALcm \| $HLcm \| $NUcm);

	# LB 30a Do not break between regional indicators.
	$RIcm $RIcm;

	#
	# Reverse Rules.
	#
	## -------------------------------------------------

	!!reverse;

	$CM+ $ALPlus;
	$CM+ $BA;
	$CM+ $BB;
	$CM+ $B2;
	$CM+ $CL;
	$CM+ $CP;
	$CM+ $EX;
	$CM+ $GL;
	$CM+ $HL;
	$CM+ $HY;
	$CM+ $H2;
	$CM+ $H3;
	$CM+ $ID;
	$CM+ $IN;
	$CM+ $IS;
	$CM+ $JL;
	$CM+ $JV;
	$CM+ $JT;
	$CM+ $NS;
	$CM+ $NU;
	$CM+ $OP;
	$CM+ $PO;
	$CM+ $PR;
	$CM+ $QU;
	$CM+ $RI;
	$CM+ $SY;
	$CM+ $WJ;
	$CM+;


	#
	# Sequences of the form (shown forwards)
	# [CANT_CM] <break> [CM] [whatever]
	# The CM needs to behave as an AL
	#
	$AL_FOLLOW $CM+ / (
	[$BK $CR $LF $NL $ZW {eof}] \|
	$SP+ $CM+ $SP \|
	$SP+ $CM* ([^$OP $CM $SP] \| [$AL {eof}])); # if LB 14 will match, need to surpress this break.
	# LB14 says OP SP* x .
	# becomes OP SP* x AL
	# becomes OP SP* x CM+ AL_FOLLOW
	#
	# Further note: the $AL in [$AL {eof}] is only to work around
	# a rule compiler bug which complains about
	# empty sets otherwise.

	#
	# Sequences of the form (shown forwards)
	# [CANT_CM] <break> [CM] <break> [PR]
	# The CM needs to behave as an AL
	# This rule is concerned about getting the second of the two <breaks> in place.
	#

	[$PR ] / $CM+ [$BK $CR $LF $NL $ZW $SP {eof}];



	# LB 4, 5, 5

	$LB4Breaks [$LB4NonBreaks-$CM];
	$LB4Breaks $CM+ $CAN_CM;
	$LF $CR;


	# LB 7 x SP
	# x ZW
	[$SP $ZW] [$LB4NonBreaks-$CM];
	[$SP $ZW] $CM+ $CAN_CM;

	# LB 8 ZW SP* <break>
	# TODO: to implement this, we need more than one look-ahead hard break in play at a time.
	# Requires an engine enhancement.
	# / $SP* $ZW

	# LB 9,10 Combining marks.
	# X $CM needs to behave like X, where X is not $SP or controls.
	# $CM not covered by the above needs to behave like $AL
	# Stick together any combining sequences that don't match other rules.
	$CM+ $CAN_CM;


	# LB 11
	$CM* $WJ $CM* $CAN_CM;
	$CM* $WJ [$LB8NonBreaks-$CM];

	$CANT_CM $CM* $WJ;
	$CM* $CAN_CM $CM* $WJ;

	# LB 12a
	# [^SP BA HY] x GL
	#
	$CM* $GL $CM* [$LB8NonBreaks-[$CM $SP $BA $HY]];

	# LB 12
	# GL x
	#
	$CANT_CM $CM* $GL;
	$CM* $CAN_CM $CM* $GL;


	# LB 13
	$CL $CM+ $CAN_CM;
	$CP $CM+ $CAN_CM;
	$EX $CM+ $CAN_CM;
	$IS $CM+ $CAN_CM;
	$SY $CM+ $CAN_CM;

	$CL [$LB8NonBreaks-$CM];
	$CP [$LB8NonBreaks-$CM];
	$EX [$LB8NonBreaks-$CM];
	$IS [$LB8NonBreaks-$CM];
	$SY [$LB8NonBreaks-$CM];

	# Rule 13 & 14 taken together for an edge case.
	# Match this, shown forward
	# OP SP+ ($CM+ behaving as $AL) (CL \| CP \| EX \| IS \| IY)
	# This really wants to chain at the $CM+ (which is acting as an $AL)
	# except for $CM chaining being disabled.
	[$CL $CP $EX $IS $SY] $CM+ $SP+ $CM* $OP;

	# LB 14 OP SP* x
	#
	$CM* $CAN_CM $SP* $CM* $OP;
	$CANT_CM $SP* $CM* $OP;
	$AL_FOLLOW? $CM+ $SP $SP* $CM* $OP; # by LB 10, behaves like $AL_FOLLOW? $AL $SP* $CM* $OP

	$AL_FOLLOW_NOCM $CM+ $SP+ $CM* $OP;
	$CM* $AL_FOLLOW_CM $CM+ $SP+ $CM* $OP;
	$SY $CM $SP+ $OP; # TODO: Experiment. Remove.



	# LB 15
	$CM* $OP $SP* $CM* $QU;

	# LB 16
	$CM* $NS $SP* $CM* ($CL \| $CP);

	# LB 17
	$CM* $B2 $SP* $CM* $B2;

	# LB 18 break after spaces
	# Nothing explicit needed here.


	#
	# LB 19
	#
	$CM* $QU $CM* $CAN_CM; # . x QU
	$CM* $QU $LB18NonBreaks;


	$CM* $CAN_CM $CM* $QU; # QU x .
	$CANT_CM $CM* $QU;

	#
	# LB 20 Break before and after CB.
	# nothing needed here.
	#

	# LB 21
	$CM* ($BA \| $HY \| $NS) $CM* [$LB20NonBreaks-$CM]; # . x (BA \| HY \| NS)

	$CM* [$LB20NonBreaks-$CM] $CM* $BB; # BB x .
	[^$CB] $CM* $BB; #

	# LB21a
	[^$CB] $CM* ($HY \| $BA) $CM* $HL;

	# LB21b (reverse)
	$CM* $HL $CM* $SY;

	# LB 22
	$CM* $IN $CM* ($ALPlus \| $HL);
	$CM* $IN $CM* $EX;
	$CM* $IN $CM* $ID;
	$CM* $IN $CM* $IN;
	$CM* $IN $CM* $NU;

	# LB 23
	$CM* $PO $CM* $ID;
	$CM* $NU $CM* ($ALPlus \| $HL);
	$CM* ($ALPlus \| $HL) $CM* $NU;

	# LB 24
	$CM* $ID $CM* $PR;
	$CM* ($ALPlus \| $HL) $CM* $PR;
	$CM* ($ALPlus \| $HL) $CM* $PO;


	# LB 25
	($CM* ($PR \| $PO))? ($CM* ($CL \| $CP))? ($CM* ($NU \| $IS \| $SY))* $CM* $NU ($CM* ($OP \| $HY))? ($CM* ($PR \| $PO))?;

	# LB 26
	$CM* ($H3 \| $H2 \| $JV \| $JL) $CM* $JL;
	$CM* ($JT \| $JV) $CM* ($H2 \| $JV);
	$CM* $JT $CM* ($H3 \| $JT);

	# LB 27
	$CM* $IN $CM* ($H3 \| $H2 \| $JT \| $JV \| $JL);
	$CM* $PO $CM* ($H3 \| $H2 \| $JT \| $JV \| $JL);
	$CM* ($H3 \| $H2 \| $JT \| $JV \| $JL) $CM* $PR;

	# LB 28
	$CM* ($ALPlus \| $HL) $CM* ($ALPlus \| $HL);


	# LB 29
	$CM* ($ALPlus \| $HL) $CM* $IS;

	# LB 30
	$CM* $OP $CM* ($ALPlus \| $HL \| $NU);
	$CM* ($ALPlus \| $HL \| $NU) $CM* $CP;

	# LB 30a
	$CM* $RI $CM* $RI;

	## -------------------------------------------------

	!!safe_reverse;

	# LB 9
	$CM+ [^$CM $BK $CR $LF $NL $ZW $SP];
	$CM+ $SP / .;

	# LB 14
	$SP+ $CM* $OP;

	# LB 15
	$SP+ $CM* $QU;

	# LB 16
	$SP+ $CM* ($CL \| $CP);

	# LB 17
	$SP+ $CM* $B2;

	# LB 21
	$CM* ($HY \| $BA) $CM* $HL;

	# LB 25
	($CM* ($IS \| $SY))+ $CM* $NU;
	($CL \| $CP) $CM* ($NU \| $IS \| $SY);

	# For dictionary-based break
	$dictionary $dictionary;

	## -------------------------------------------------

	!!safe_forward;

	# Skip forward over all character classes that are involved in
	# rules containing patterns with possibly more than one char
	# of context.
	#
	# It might be slightly more efficient to have specific rules
	# instead of one generic one, but only if we could
	# turn off rule chaining. We don't want to move more
	# than necessary.
	#
	[$CM $OP $QU $CL $CP $B2 $PR $HY $BA $SP $dictionary]+ [^$CM $OP $QU $CL $CP $B2 $PR $HY $BA $dictionary];
	$dictionary $dictionary;