From 620f3a1307a1e166cebc89aeb76a7854a545c238 Mon Sep 17 00:00:00 2001 From: "Philip.Hazel" Date: Sat, 13 Jul 2019 11:12:03 +0000 Subject: [PATCH] Implement non-atomic positive assertions. --- ChangeLog | 2 + HACKING | 34 +- doc/html/pcre2compat.html | 7 +- doc/html/pcre2pattern.html | 137 +++-- doc/html/pcre2syntax.html | 50 +- doc/pcre2.txt | 1100 +++++++++++++++++++----------------- doc/pcre2compat.3 | 8 +- doc/pcre2pattern.3 | 99 +++- doc/pcre2syntax.3 | 16 +- src/pcre2.h.in | 1 + src/pcre2_auto_possess.c | 7 + src/pcre2_compile.c | 110 +++- src/pcre2_dfa_match.c | 4 + src/pcre2_error.c | 1 + src/pcre2_internal.h | 95 ++-- src/pcre2_match.c | 14 +- src/pcre2_printint.c | 2 + src/pcre2_study.c | 4 + testdata/testinput2 | 29 + testdata/testoutput2 | 89 ++- testdata/testoutput5 | 8 +- 21 files changed, 1134 insertions(+), 683 deletions(-) diff --git a/ChangeLog b/ChangeLog index 23589ac..e846d46 100644 --- a/ChangeLog +++ b/ChangeLog @@ -88,6 +88,8 @@ otherwise), an atomic group, or a recursion. 17. Check for integer overflow when computing lookbehind lengths. Fixes Clusterfuzz issue 15636. +18. Implement non-atomic positive lookaround assertions. + Version 10.33 16-April-2019 --------------------------- diff --git a/HACKING b/HACKING index f99616a..20faf8f 100644 --- a/HACKING +++ b/HACKING @@ -195,6 +195,7 @@ META_END End of pattern (this value is 0x80000000) META_FAIL (*FAIL) META_KET ) closing parenthesis META_LOOKAHEAD (?= start of lookahead +META_LOOKAHEAD_NA (*napla: start of non-atomic lookahead META_LOOKAHEADNOT (?! start of negative lookahead META_NOCAPTURE (?: no capture parens META_PLUS + @@ -286,8 +287,9 @@ The following are also followed just by an offset, but also the lower 16 bits of the main word contain the length of the first branch of the lookbehind group; this is used when generating OP_REVERSE for that branch. -META_LOOKBEHIND (?<= -META_LOOKBEHINDNOT (? +
+(m) PCRE2 supports non-atomic positive lookaround assertions. This is an +extension to the lookaround facilities. The default, Perl-compatible +lookarounds are atomic.

18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa @@ -234,7 +239,7 @@ Cambridge, England. REVISION

-Last updated: 12 February 2019 +Last updated: 13 July 2019
Copyright © 1997-2019 University of Cambridge.
diff --git a/doc/html/pcre2pattern.html b/doc/html/pcre2pattern.html index 14f78c8..8188a65 100644 --- a/doc/html/pcre2pattern.html +++ b/doc/html/pcre2pattern.html @@ -33,17 +33,18 @@ please consult the man page, in case the conversion went wrong.

  • ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
  • BACKREFERENCES
  • ASSERTIONS -
  • SCRIPT RUNS -
  • CONDITIONAL GROUPS -
  • COMMENTS -
  • RECURSIVE PATTERNS -
  • GROUPS AS SUBROUTINES -
  • ONIGURUMA SUBROUTINE SYNTAX -
  • CALLOUTS -
  • BACKTRACKING CONTROL -
  • SEE ALSO -
  • AUTHOR -
  • REVISION +
  • NON-ATOMIC ASSERTIONS +
  • SCRIPT RUNS +
  • CONDITIONAL GROUPS +
  • COMMENTS +
  • RECURSIVE PATTERNS +
  • GROUPS AS SUBROUTINES +
  • ONIGURUMA SUBROUTINE SYNTAX +
  • CALLOUTS +
  • BACKTRACKING CONTROL +
  • SEE ALSO +
  • AUTHOR +
  • REVISION
    PCRE2 REGULAR EXPRESSION DETAILS

    @@ -2364,19 +2365,23 @@ those that look behind it, and in each case an assertion may be positive (must match for the assertion to be true) or negative (must not match for the assertion to be true). An assertion group is matched in the normal way, and if it is true, matching continues after it, but with the matching position -in the subject string is was it was before the assertion was processed. +in the subject string reset to what it was before the assertion was processed.

    -A lookaround assertion may also appear as the condition in a +The Perl-compatible lookaround assertions are atomic. If an assertion is true, +but there is a subsequent matching failure, there is no backtracking into the +assertion. However, there are some cases where non-atomic assertions can be +useful. PCRE2 has some support for these, described in the section entitled +"Non-atomic assertions" +below, but they are not Perl-compatible. +

    +

    +A lookaround assertion may appear as the condition in a conditional group (see below). In this case, the result of matching the assertion determines which branch of the condition is followed.

    -Lookaround assertions are atomic. If an assertion is true, but there is a -subsequent matching failure, there is no backtracking into the assertion. -

    -

    Assertion groups are not capture groups. If an assertion contains capture groups within it, these are counted for the purposes of numbering the capture groups in the whole pattern. Within each branch of an assertion, locally @@ -2429,11 +2434,11 @@ The assertion is obeyed just once when encountered during matching. Alphabetic assertion names

    -Traditionally, symbolic sequences such as (?= and (?<= have been used to specify -lookaround assertions. Perl 5.28 introduced some experimental alphabetic -alternatives which might be easier to remember. They all start with (* instead -of (? and must be written using lower case letters. PCRE2 supports the -following synonyms: +Traditionally, symbolic sequences such as (?= and (?<= have been used to +specify lookaround assertions. Perl 5.28 introduced some experimental +alphabetic alternatives which might be easier to remember. They all start with +(* instead of (? and must be written using lower case letters. PCRE2 supports +the following synonyms: 

       (*positive_lookahead:  or (*pla: is the same as (?=
   (*negative_lookahead:  or (*nla: is the same as (?!
@@ -2606,8 +2611,63 @@ preceded by "foo", while
    is another pattern that matches "foo" preceded by three digits and any three characters that are not "999". +

    +
    NON-ATOMIC ASSERTIONS
    +

    +The traditional Perl-compatible lookaround assertions are atomic. That is, if +an assertion is true, but there is a subsequent matching failure, there is no +backtracking into the assertion. However, there are some cases where non-atomic +positive assertions can be useful. PCRE2 provides these using the following +syntax: +

    +  (*non_atomic_positive_lookahead:  or (*napla:
+  (*non_atomic_positive_lookbehind: or (*naplb: 
+
    +Consider the problem of finding the right-most word in a string that also +appears earlier in the string, that is, it must appear at least twice in total. +This pattern returns the required result as captured substring 1: +
    +  ^(?x)(*napla: .* \b(\w++)) (?> .*? \b\1\b ){2}
+
    +For a subject such as "word1 word2 word3 word2 word3 word4" the result is +"word3". How does it work? At the start, ^(?x) anchors the pattern and sets the +"x" option, which causes white space (introduced for readability) to be +ignored. Inside the assertion, the greedy .* at first consumes the entire +string, but then has to backtrack until the rest of the assertion can match a +word, which is captured by group 1. In other words, when the assertion first +succeeds, it captures the right-most word in the string.

    -
    SCRIPT RUNS
    +

    +The current matching point is then reset to the start of the subject, and the +rest of the pattern match checks for two occurrences of the captured word, +using an ungreedy .*? to scan from the left. If this succeeds, we are done, but +if the last word in the string does not occur twice, this part of the pattern +fails. If a traditional atomic lookhead (?= or (*pla: had been used, the +assertion could not be re-entered, and the whole match would fail. The pattern +would succeed only if the very last word in the subject was found twice. +

    +

    +Using a non-atomic lookahead, however, means that when the last word does not +occur twice in the string, the lookahead can backtrack and find the second-last +word, and so on, until either the match succeeds, or all words have been +tested. +

    +

    +Two conditions must be met for a non-atomic assertion to be useful: the +contents of one or more capturing groups must change after a backtrack into the +assertion, and there must be a backreference to a changed group later in the +pattern. If this is not the case, the rest of the pattern match fails exactly +as before because nothing has changed, so using a non-atomic assertion just +wastes resources. +

    +

    +Non-atomic assertions are not supported by the alternative matching function +pcre2_dfa_match(). They are also not supported by JIT (but may be in +future). Note that assertions that appear as conditions for +conditional groups +(see below) must be atomic. +

    +
    SCRIPT RUNS

    In concept, a script run is a sequence of characters that are all from the same Unicode script such as Latin or Greek. However, because some scripts are @@ -2669,7 +2729,7 @@ parentheses. should not be used within a script run group, because it causes an immediate exit from the group, bypassing the script run checking.

    -
    CONDITIONAL GROUPS
    +
    CONDITIONAL GROUPS

    It is possible to cause the matching process to obey a pattern fragment conditionally or to choose between two alternative fragments, depending on @@ -2845,8 +2905,13 @@ Assertion conditions

    If the condition is not in any of the above formats, it must be a parenthesized assertion. This may be a positive or negative lookahead or lookbehind -assertion. Consider this pattern, again containing non-significant white space, -and with the two alternatives on the second line: +assertion. However, it must be a traditional atomic assertion, not one of the +PCRE2-specific +non-atomic assertions. +

    +

    +Consider this pattern, again containing non-significant white space, and with +the two alternatives on the second line: 

       (?(?=[^a-z]*[a-z])
   \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
@@ -2865,7 +2930,7 @@ positive and negative assertions, because matching always continues after the
 assertion, whether it succeeds or fails. (Compare non-conditional assertions,
 for which captures are retained only for positive assertions that succeed.)
 
    
-
    COMMENTS
    
+
    COMMENTS
    
 
    
 There are two ways of including comments in patterns that are processed by
 PCRE2. In both cases, the start of the comment must not be in a character
@@ -2895,7 +2960,7 @@ a newline in the pattern. The sequence \n is still literal at this stage, so
 it does not terminate the comment. Only an actual character with the code value
 0x0a (the default newline) does so.
 
    
-
    RECURSIVE PATTERNS
    
+
    RECURSIVE PATTERNS
    
 
    
 Consider the problem of matching a string in parentheses, allowing for
 unlimited nested parentheses. Without the use of recursion, the best that can
@@ -3083,7 +3148,7 @@ alternative matches "a" and then recurses. In the recursion, \1 does now match
 "b" and so the whole match succeeds. This match used to fail in Perl, but in
 later versions (I tried 5.024) it now works.
 
    
-
    GROUPS AS SUBROUTINES
    
+
    GROUPS AS SUBROUTINES
    
 
    
 If the syntax for a recursive group call (either by number or by name) is used
 outside the parentheses to which it refers, it operates a bit like a subroutine
@@ -3131,7 +3196,7 @@ in groups when called as subroutines is described in the section entitled
 "Backtracking verbs in subroutines"
 below.
 
    
-
    ONIGURUMA SUBROUTINE SYNTAX
    
+
    ONIGURUMA SUBROUTINE SYNTAX
    
 
    
 For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or
 a number enclosed either in angle brackets or single quotes, is an alternative
@@ -3149,7 +3214,7 @@ plus or a minus sign it is taken as a relative reference. For example:
 Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
 synonymous. The former is a backreference; the latter is a subroutine call.
 
    
-
    CALLOUTS
    
+
    CALLOUTS
    
 
    
 Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl
 code to be obeyed in the middle of matching a regular expression. This makes it
@@ -3225,7 +3290,7 @@ example:
    The doubling is removed before the string is passed to the callout function.

    -
    BACKTRACKING CONTROL
    +
    BACKTRACKING CONTROL

    There are a number of special "Backtracking Control Verbs" (to use Perl's terminology) that modify the behaviour of backtracking during matching. They @@ -3739,12 +3804,12 @@ enclosing group that has alternatives (its normal behaviour). However, if there is no such group within the subroutine's group, the subroutine match fails and there is a backtrack at the outer level.

    -
    SEE ALSO
    +
    SEE ALSO

    pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3), pcre2(3).

    -
    AUTHOR
    +
    AUTHOR

    Philip Hazel
    @@ -3753,9 +3818,9 @@ University Computing Service Cambridge, England.

    -
    REVISION
    +
    REVISION

    -Last updated: 22 June 2019 +Last updated: 13 July 2019
    Copyright © 1997-2019 University of Cambridge.
    diff --git a/doc/html/pcre2syntax.html b/doc/html/pcre2syntax.html index e3dc186..db8689d 100644 --- a/doc/html/pcre2syntax.html +++ b/doc/html/pcre2syntax.html @@ -32,15 +32,16 @@ please consult the man page, in case the conversion went wrong.

  • NEWLINE CONVENTION
  • WHAT \R MATCHES
  • LOOKAHEAD AND LOOKBEHIND ASSERTIONS -
  • SCRIPT RUNS -
  • BACKREFERENCES -
  • SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) -
  • CONDITIONAL PATTERNS -
  • BACKTRACKING CONTROL -
  • CALLOUTS -
  • SEE ALSO -
  • AUTHOR -
  • REVISION +
  • NON-ATOMIC LOOKAROUND ASSERTIONS +
  • SCRIPT RUNS +
  • BACKREFERENCES +
  • SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) +
  • CONDITIONAL PATTERNS +
  • BACKTRACKING CONTROL +
  • CALLOUTS +
  • SEE ALSO +
  • AUTHOR +
  • REVISION
    PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY

    @@ -544,7 +545,18 @@ setting with a similar syntax. Each top-level branch of a lookbehind must be of a fixed length.

    -
    SCRIPT RUNS
    +
    NON-ATOMIC LOOKAROUND ASSERTIONS
    +

    +These assertions are specific to PCRE2 and are not Perl-compatible. +

    +  (*napla:...)                  
+  (*non_atomic_positive_lookahead:...)
+
+  (*naplb:...)
+  (*non_atomic_positive_lookbehind:...)
+
    +

    +
    SCRIPT RUNS

       (*script_run:...)           ) script run, can be backtracked into
@@ -554,7 +566,7 @@ Each top-level branch of a lookbehind must be of a fixed length.
   (*asr:...)                  )

    -
    BACKREFERENCES
    +
    BACKREFERENCES

       \n              reference by number (can be ambiguous)
@@ -571,7 +583,7 @@ Each top-level branch of a lookbehind must be of a fixed length.
   (?P=name)       reference by name (Python)

    -
    SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
    +
    SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)

       (?R)            recurse whole pattern
@@ -590,7 +602,7 @@ Each top-level branch of a lookbehind must be of a fixed length.
   \g'-n'          call subroutine by relative number (PCRE2 extension)

    -
    CONDITIONAL PATTERNS
    +
    CONDITIONAL PATTERNS

       (?(condition)yes-pattern)
@@ -613,7 +625,7 @@ Note the ambiguity of (?(R) and (?(Rn) which might be named reference
 conditions or recursion tests. Such a condition is interpreted as a reference
 condition if the relevant named group exists.
 
    
-
    BACKTRACKING CONTROL
    
+
    BACKTRACKING CONTROL
    
 
    
 All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) the
 name is mandatory, for the others it is optional. (*SKIP) changes its behaviour
@@ -640,7 +652,7 @@ pattern is not anchored.
 The effect of one of these verbs in a group called as a subroutine is confined
 to the subroutine call.
 
    
-
    CALLOUTS
    
+
    CALLOUTS
    
 
    
 
       (?C)            callout (assumed number 0)
@@ -651,12 +663,12 @@ The allowed string delimiters are ` ' " ^ % # $ (which are the same for the
 start and the end), and the starting delimiter { matched with the ending
 delimiter }. To encode the ending delimiter within the string, double it.
 
    
-
    SEE ALSO
    
+
    SEE ALSO
    
 
    
 pcre2pattern(3), pcre2api(3), pcre2callout(3),
 pcre2matching(3), pcre2(3).
 
    
-
    AUTHOR
    
+
    AUTHOR
    
 
    
 Philip Hazel
 
    
@@ -665,9 +677,9 @@ University Computing Service
 Cambridge, England.
 
    
 
    
-
    REVISION
    
+
    REVISION
    
 
    
-Last updated: 11 February 2019
+Last updated: 12 July 2019
 
    
 Copyright © 1997-2019 University of Cambridge.
 
    
diff --git a/doc/pcre2.txt b/doc/pcre2.txt
index 7a9fd94..33e6096 100644
--- a/doc/pcre2.txt
+++ b/doc/pcre2.txt
@@ -4887,6 +4887,10 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
        at the start of a pattern that  set  overall  options  that  cannot  be
        changed within the pattern.
 
+       (m)  PCRE2  supports non-atomic positive lookaround assertions. This is
+       an extension to the lookaround facilities. The default, Perl-compatible
+       lookarounds are atomic.
+
        18.  The  Perl  /a modifier restricts /d numbers to pure ascii, and the
        /aa modifier restricts /i case-insensitive matching to pure ascii,  ig-
        noring  Unicode  rules.  This  separation  cannot  be  represented with
@@ -4909,7 +4913,7 @@ AUTHOR
 
 REVISION
 
-       Last updated: 12 February 2019
+       Last updated: 13 July 2019
        Copyright (c) 1997-2019 University of Cambridge.
 ------------------------------------------------------------------------------
  
@@ -8140,66 +8144,69 @@ ASSERTIONS
        sertion  may  be  positive (must match for the assertion to be true) or
        negative (must not match for the assertion to be  true).  An  assertion
        group is matched in the normal way, and if it is true, matching contin-
-       ues after it, but with the matching position in the subject  string  is
-       was it was before the assertion was processed.
+       ues after it, but with the matching position in the subject string  re-
+       set to what it was before the assertion was processed.
 
-       A  lookaround  assertion  may  also appear as the condition in a condi-
-       tional group (see below). In this case, the result of matching the  as-
-       sertion determines which branch of the condition is followed.
+       The  Perl-compatible  lookaround assertions are atomic. If an assertion
+       is true, but there is a subsequent matching failure, there is no  back-
+       tracking  into  the assertion. However, there are some cases where non-
+       atomic assertions can be useful. PCRE2 has some support for these,  de-
+       scribed in the section entitled "Non-atomic assertions" below, but they
+       are not Perl-compatible.
 
-       Lookaround assertions are atomic. If an assertion is true, but there is
-       a subsequent matching failure, there is no backtracking into the asser-
-       tion.
+       A lookaround assertion may appear as the  condition  in  a  conditional
+       group  (see  below). In this case, the result of matching the assertion
+       determines which branch of the condition is followed.
 
-       Assertion  groups are not capture groups. If an assertion contains cap-
-       ture groups within it, these are counted for the purposes of  numbering
-       the  capture  groups in the whole pattern. Within each branch of an as-
-       sertion, locally captured substrings may be  referenced  in  the  usual
-       way.  For  example,  a  sequence such as (.)\g{-1} can be used to check
+       Assertion groups are not capture groups. If an assertion contains  cap-
+       ture  groups within it, these are counted for the purposes of numbering
+       the capture groups in the whole pattern. Within each branch of  an  as-
+       sertion,  locally  captured  substrings  may be referenced in the usual
+       way. For example, a sequence such as (.)\g{-1} can  be  used  to  check
        that two adjacent characters are the same.
 
-       When a branch within an assertion fails to match, any  substrings  that
-       were  captured  are  discarded (as happens with any pattern branch that
-       fails to match). A  negative  assertion  is  true  only  when  all  its
+       When  a  branch within an assertion fails to match, any substrings that
+       were captured are discarded (as happens with any  pattern  branch  that
+       fails  to  match).  A  negative  assertion  is  true  only when all its
        branches fail to match; this means that no captured substrings are ever
-       retained after a successful negative assertion. When an assertion  con-
+       retained  after a successful negative assertion. When an assertion con-
        tains a matching branch, what happens depends on the type of assertion.
 
-       For  a  positive  assertion, internally captured substrings in the suc-
-       cessful branch are retained, and matching continues with the next  pat-
-       tern  item  after  the  assertion. For a negative assertion, a matching
-       branch means that the assertion is not true. If such  an  assertion  is
-       being  used as a condition in a conditional group (see below), captured
-       substrings are retained,  because  matching  continues  with  the  "no"
+       For a positive assertion, internally captured substrings  in  the  suc-
+       cessful  branch are retained, and matching continues with the next pat-
+       tern item after the assertion. For a  negative  assertion,  a  matching
+       branch  means  that  the assertion is not true. If such an assertion is
+       being used as a condition in a conditional group (see below),  captured
+       substrings  are  retained,  because  matching  continues  with the "no"
        branch of the condition. For other failing negative assertions, control
        passes to the previous backtracking point, thus discarding any captured
        strings within the assertion.
 
-       For  compatibility  with  Perl,  most assertion groups may be repeated;
-       though it makes no sense to assert the same thing  several  times,  the
+       For compatibility with Perl, most assertion  groups  may  be  repeated;
+       though  it  makes  no sense to assert the same thing several times, the
        side effect of capturing may occasionally be useful. However, an asser-
-       tion that forms the condition for a conditional group may not be  quan-
+       tion  that forms the condition for a conditional group may not be quan-
        tified. In practice, for other assertions, there only three cases:
 
-       (1)  If  the  quantifier  is  {0}, the assertion is never obeyed during
-       matching.  However, it may contain internal  capture  groups  that  are
+       (1) If the quantifier is {0}, the  assertion  is  never  obeyed  during
+       matching.   However,  it  may  contain internal capture groups that are
        called from elsewhere via the subroutine mechanism.
 
-       (2)  If quantifier is {0,n} where n is greater than zero, it is treated
-       as if it were {0,1}. At run time, the rest  of  the  pattern  match  is
+       (2) If quantifier is {0,n} where n is greater than zero, it is  treated
+       as  if  it  were  {0,1}.  At run time, the rest of the pattern match is
        tried with and without the assertion, the order depending on the greed-
        iness of the quantifier.
 
-       (3) If the minimum repetition is greater than zero, the  quantifier  is
-       ignored.   The  assertion  is  obeyed just once when encountered during
+       (3)  If  the minimum repetition is greater than zero, the quantifier is
+       ignored.  The assertion is obeyed just  once  when  encountered  during
        matching.
 
    Alphabetic assertion names
 
-       Traditionally, symbolic sequences such as (?= and (?<= have  been  used
-       to  specify lookaround assertions. Perl 5.28 introduced some experimen-
+       Traditionally,  symbolic  sequences such as (?= and (?<= have been used
+       to specify lookaround assertions. Perl 5.28 introduced some  experimen-
        tal alphabetic alternatives which might be easier to remember. They all
-       start  with  (* instead of (? and must be written using lower case let-
+       start with (* instead of (? and must be written using lower  case  let-
        ters. PCRE2 supports the following synonyms:
 
          (*positive_lookahead:  or (*pla: is the same as (?=
@@ -8207,8 +8214,8 @@ ASSERTIONS
          (*positive_lookbehind: or (*plb: is the same as (?<=
          (*negative_lookbehind: or (*nlb: is the same as (? .*? \b\1\b ){2}
+
+       For a subject such as "word1 word2 word3 word2 word3 word4" the  result
+       is  "word3".  How does it work? At the start, ^(?x) anchors the pattern
+       and sets the "x" option, which causes white space (introduced for read-
+       ability)  to  be  ignored. Inside the assertion, the greedy .* at first
+       consumes the entire string, but then has to backtrack until the rest of
+       the  assertion can match a word, which is captured by group 1. In other
+       words, when the assertion first succeeds, it  captures  the  right-most
+       word in the string.
+
+       The  current  matching point is then reset to the start of the subject,
+       and the rest of the pattern match checks for  two  occurrences  of  the
+       captured  word,  using  an  ungreedy .*? to scan from the left. If this
+       succeeds, we are done, but if the last word in the string does not  oc-
+       cur  twice,  this  part  of  the pattern fails. If a traditional atomic
+       lookhead (?= or (*pla: had been used, the assertion could not be re-en-
+       tered,  and  the whole match would fail. The pattern would succeed only
+       if the very last word in the subject was found twice.
+
+       Using a non-atomic lookahead, however, means that when  the  last  word
+       does  not  occur  twice  in the string, the lookahead can backtrack and
+       find the second-last word, and so on, until either the match  succeeds,
+       or all words have been tested.
+
+       Two conditions must be met for a non-atomic assertion to be useful: the
+       contents of one or more capturing groups must change after a  backtrack
+       into  the  assertion,  and  there  must be a backreference to a changed
+       group later in the pattern. If this is not the case, the  rest  of  the
+       pattern  match  fails exactly as before because nothing has changed, so
+       using a non-atomic assertion just wastes resources.
+
+       Non-atomic assertions are not supported  by  the  alternative  matching
+       function pcre2_dfa_match(). They are also not supported by JIT (but may
+       be in future). Note that assertions that appear as conditions for  con-
+       ditional groups (see below) must be atomic.
+
+
 SCRIPT RUNS
 
-       In concept, a script run is a sequence of characters that are all  from
-       the  same  Unicode script such as Latin or Greek. However, because some
-       scripts are commonly used together, and because  some  diacritical  and
-       other  marks  are  used  with  multiple scripts, it is not that simple.
+       In  concept, a script run is a sequence of characters that are all from
+       the same Unicode script such as Latin or Greek. However,  because  some
+       scripts  are  commonly  used together, and because some diacritical and
+       other marks are used with multiple scripts,  it  is  not  that  simple.
        There is a full description of the rules that PCRE2 uses in the section
        entitled "Script Runs" in the pcre2unicode documentation.
 
-       If  part  of a pattern is enclosed between (*script_run: or (*sr: and a
-       closing parenthesis, it fails if the sequence  of  characters  that  it
-       matches  are not a script run. After a failure, normal backtracking oc-
-       curs. Script runs can be used to detect spoofing attacks using  charac-
-       ters  that  look  the  same, but are from different scripts. The string
-       "paypal.com" is an infamous example, where the letters could be a  mix-
+       If part of a pattern is enclosed between (*script_run: or (*sr:  and  a
+       closing  parenthesis,  it  fails  if the sequence of characters that it
+       matches are not a script run. After a failure, normal backtracking  oc-
+       curs.  Script runs can be used to detect spoofing attacks using charac-
+       ters that look the same, but are from  different  scripts.  The  string
+       "paypal.com"  is an infamous example, where the letters could be a mix-
        ture of Latin and Cyrillic. This pattern ensures that the matched char-
        acters in a sequence of non-spaces that follow white space are a script
        run:
 
          \s+(*sr:\S+)
 
-       To  be  sure  that  they are all from the Latin script (for example), a
+       To be sure that they are all from the Latin  script  (for  example),  a
        lookahead can be used:
 
          \s+(?=\p{Latin})(*sr:\S+)
 
        This works as long as the first character is expected to be a character
-       in  that  script,  and  not (for example) punctuation, which is allowed
-       with any script. If this is not the case, a more creative lookahead  is
-       needed.  For  example, if digits, underscore, and dots are permitted at
+       in that script, and not (for example)  punctuation,  which  is  allowed
+       with  any script. If this is not the case, a more creative lookahead is
+       needed. For example, if digits, underscore, and dots are  permitted  at
        the start:
 
          \s+(?=[0-9_.]*\p{Latin})(*sr:\S+)
 
 
-       In many cases, backtracking into a script run pattern fragment  is  not
-       desirable.  The  script run can employ an atomic group to prevent this.
-       Because this is a common requirement, a shorthand notation is  provided
+       In  many  cases, backtracking into a script run pattern fragment is not
+       desirable. The script run can employ an atomic group to  prevent  this.
+       Because  this is a common requirement, a shorthand notation is provided
        by (*atomic_script_run: or (*asr:
 
          (*asr:...) is the same as (*sr:(?>...))
@@ -8407,13 +8468,13 @@ SCRIPT RUNS
        Note that the atomic group is inside the script run. Putting it outside
        would not prevent backtracking into the script run pattern.
 
-       Support for script runs is not available if PCRE2 is  compiled  without
+       Support  for  script runs is not available if PCRE2 is compiled without
        Unicode support. A compile-time error is given if any of the above con-
-       structs is encountered. Script runs are not supported by the  alternate
-       matching  function,  pcre2_dfa_match() because they use the same mecha-
+       structs  is encountered. Script runs are not supported by the alternate
+       matching function, pcre2_dfa_match() because they use the  same  mecha-
        nism as capturing parentheses.
 
-       Warning: The (*ACCEPT) control verb (see  below)  should  not  be  used
+       Warning:  The  (*ACCEPT)  control  verb  (see below) should not be used
        within a script run group, because it causes an immediate exit from the
        group, bypassing the script run checking.
 
@@ -8422,116 +8483,116 @@ CONDITIONAL GROUPS
 
        It is possible to cause the matching process to obey a pattern fragment
        conditionally or to choose between two alternative fragments, depending
-       on the result of an assertion, or whether a specific capture group  has
+       on  the result of an assertion, or whether a specific capture group has
        already been matched. The two possible forms of conditional group are:
 
          (?(condition)yes-pattern)
          (?(condition)yes-pattern|no-pattern)
 
-       If  the  condition is satisfied, the yes-pattern is used; otherwise the
-       no-pattern (if present) is used. An absent no-pattern is equivalent  to
-       an  empty string (it always matches). If there are more than two alter-
-       natives in the group, a compile-time error occurs. Each of the two  al-
+       If the condition is satisfied, the yes-pattern is used;  otherwise  the
+       no-pattern  (if present) is used. An absent no-pattern is equivalent to
+       an empty string (it always matches). If there are more than two  alter-
+       natives  in the group, a compile-time error occurs. Each of the two al-
        ternatives may itself contain nested groups of any form, including con-
-       ditional groups; the restriction to two alternatives  applies  only  at
-       the  level of the condition itself. This pattern fragment is an example
+       ditional  groups;  the  restriction to two alternatives applies only at
+       the level of the condition itself. This pattern fragment is an  example
        where the alternatives are complex:
 
          (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
 
 
        There are five kinds of condition: references to capture groups, refer-
-       ences  to  recursion,  two pseudo-conditions called DEFINE and VERSION,
+       ences to recursion, two pseudo-conditions called  DEFINE  and  VERSION,
        and assertions.
 
    Checking for a used capture group by number
 
-       If the text between the parentheses consists of a sequence  of  digits,
-       the  condition is true if a capture group of that number has previously
-       matched. If there is more than one capture group with the  same  number
-       (see  the earlier section about duplicate group numbers), the condition
+       If  the  text between the parentheses consists of a sequence of digits,
+       the condition is true if a capture group of that number has  previously
+       matched.  If  there is more than one capture group with the same number
+       (see the earlier section about duplicate group numbers), the  condition
        is true if any of them have matched. An alternative notation is to pre-
        cede the digits with a plus or minus sign. In this case, the group num-
-       ber is relative rather than absolute. The most recently opened  capture
-       group  can be referenced by (?(-1), the next most recent by (?(-2), and
-       so on. Inside loops it can also  make  sense  to  refer  to  subsequent
-       groups.  The next capture group can be referenced as (?(+1), and so on.
-       (The value zero in any of these forms is not used; it provokes  a  com-
+       ber  is relative rather than absolute. The most recently opened capture
+       group can be referenced by (?(-1), the next most recent by (?(-2),  and
+       so  on.  Inside  loops  it  can  also make sense to refer to subsequent
+       groups. The next capture group can be referenced as (?(+1), and so  on.
+       (The  value  zero in any of these forms is not used; it provokes a com-
        pile-time error.)
 
-       Consider  the  following  pattern, which contains non-significant white
-       space to make it more readable (assume the PCRE2_EXTENDED  option)  and
+       Consider the following pattern, which  contains  non-significant  white
+       space  to  make it more readable (assume the PCRE2_EXTENDED option) and
        to divide it into three parts for ease of discussion:
 
          ( \( )?    [^()]+    (?(1) \) )
 
-       The  first  part  matches  an optional opening parenthesis, and if that
+       The first part matches an optional opening  parenthesis,  and  if  that
        character is present, sets it as the first captured substring. The sec-
-       ond  part  matches one or more characters that are not parentheses. The
-       third part is a conditional group that tests whether or not  the  first
-       capture  group  matched. If it did, that is, if subject started with an
-       opening parenthesis, the condition is true, and so the  yes-pattern  is
-       executed  and  a  closing parenthesis is required. Otherwise, since no-
+       ond part matches one or more characters that are not  parentheses.  The
+       third  part  is a conditional group that tests whether or not the first
+       capture group matched. If it did, that is, if subject started  with  an
+       opening  parenthesis,  the condition is true, and so the yes-pattern is
+       executed and a closing parenthesis is required.  Otherwise,  since  no-
        pattern is not present, the conditional group matches nothing. In other
-       words,  this  pattern matches a sequence of non-parentheses, optionally
+       words, this pattern matches a sequence of  non-parentheses,  optionally
        enclosed in parentheses.
 
-       If you were embedding this pattern in a larger one,  you  could  use  a
+       If  you  were  embedding  this pattern in a larger one, you could use a
        relative reference:
 
          ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
 
-       This  makes  the  fragment independent of the parentheses in the larger
+       This makes the fragment independent of the parentheses  in  the  larger
        pattern.
 
    Checking for a used capture group by name
 
-       Perl uses the syntax (?()...) or (?('name')...)  to  test  for  a
-       used  capture group by name. For compatibility with earlier versions of
-       PCRE1, which had this facility before Perl, the syntax (?(name)...)  is
-       also  recognized.   Note, however, that undelimited names consisting of
-       the letter R followed by digits are ambiguous (see the  following  sec-
+       Perl  uses  the  syntax  (?()...) or (?('name')...) to test for a
+       used capture group by name. For compatibility with earlier versions  of
+       PCRE1,  which had this facility before Perl, the syntax (?(name)...) is
+       also recognized.  Note, however, that undelimited names  consisting  of
+       the  letter  R followed by digits are ambiguous (see the following sec-
        tion). Rewriting the above example to use a named group gives this:
 
          (? \( )?    [^()]+    (?() \) )
 
-       If  the  name used in a condition of this kind is a duplicate, the test
-       is applied to all groups of the same name, and is true if  any  one  of
+       If the name used in a condition of this kind is a duplicate,  the  test
+       is  applied  to  all groups of the same name, and is true if any one of
        them has matched.
 
    Checking for pattern recursion
 
-       "Recursion"  in  this sense refers to any subroutine-like call from one
-       part of the pattern to another, whether or not it  is  actually  recur-
-       sive.  See  the  sections  entitled "Recursive patterns" and "Groups as
+       "Recursion" in this sense refers to any subroutine-like call  from  one
+       part  of  the  pattern to another, whether or not it is actually recur-
+       sive. See the sections entitled "Recursive  patterns"  and  "Groups  as
        subroutines" below for details of recursion and subroutine calls.
 
-       If a condition is the string (R), and there is no  capture  group  with
-       the  name R, the condition is true if matching is currently in a recur-
-       sion or subroutine call to the whole pattern or any capture  group.  If
-       digits  follow  the letter R, and there is no group with that name, the
-       condition is true if the most recent call is  into  a  group  with  the
-       given  number,  which must exist somewhere in the overall pattern. This
+       If  a  condition  is the string (R), and there is no capture group with
+       the name R, the condition is true if matching is currently in a  recur-
+       sion  or  subroutine call to the whole pattern or any capture group. If
+       digits follow the letter R, and there is no group with that  name,  the
+       condition  is  true  if  the  most recent call is into a group with the
+       given number, which must exist somewhere in the overall  pattern.  This
        is a contrived example that is equivalent to a+b:
 
          ((?(R1)a+|(?1)b))
 
-       However, in both cases, if there is a capture  group  with  a  matching
-       name,  the  condition tests for its being set, as described in the sec-
-       tion above, instead of testing for recursion. For example,  creating  a
-       group  with  the  name  R1  by adding (?) to the above pattern com-
+       However,  in  both  cases,  if there is a capture group with a matching
+       name, the condition tests for its being set, as described in  the  sec-
+       tion  above,  instead of testing for recursion. For example, creating a
+       group with the name R1 by adding (?)  to  the  above  pattern  com-
        pletely changes its meaning.
 
        If a name preceded by ampersand follows the letter R, for example:
 
          (?(R&name)...)
 
-       the condition is true if the most recent recursion is into a  group  of
+       the  condition  is true if the most recent recursion is into a group of
        that name (which must exist within the pattern).
 
        This condition does not check the entire recursion stack. It tests only
-       the current level. If the name used in a condition of this  kind  is  a
-       duplicate,  the  test is applied to all groups of the same name, and is
+       the  current  level.  If the name used in a condition of this kind is a
+       duplicate, the test is applied to all groups of the same name,  and  is
        true if any one of them is the most recent recursion.
 
        At "top level", all these recursion test conditions are false.
@@ -8539,109 +8600,111 @@ CONDITIONAL GROUPS
    Defining capture groups for use by reference only
 
        If the condition is the string (DEFINE), the condition is always false,
-       even  if there is a group with the name DEFINE. In this case, there may
+       even if there is a group with the name DEFINE. In this case, there  may
        be only one alternative in the rest of the conditional group. It is al-
-       ways  skipped if control reaches this point in the pattern; the idea of
-       DEFINE is that it can be used to define subroutines that can be  refer-
-       enced  from elsewhere. (The use of subroutines is described below.) For
-       example, a pattern to match an IPv4 address  such  as  "192.168.23.245"
+       ways skipped if control reaches this point in the pattern; the idea  of
+       DEFINE  is that it can be used to define subroutines that can be refer-
+       enced from elsewhere. (The use of subroutines is described below.)  For
+       example,  a  pattern  to match an IPv4 address such as "192.168.23.245"
        could be written like this (ignore white space and line breaks):
 
          (?(DEFINE) (? 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
          \b (?&byte) (\.(?&byte)){3} \b
 
-       The  first part of the pattern is a DEFINE group inside which a another
-       group named "byte" is defined. This matches an individual component  of
-       an  IPv4  address  (a number less than 256). When matching takes place,
-       this part of the pattern is skipped because DEFINE acts  like  a  false
-       condition.  The  rest of the pattern uses references to the named group
-       to match the four dot-separated components of an IPv4 address,  insist-
+       The first part of the pattern is a DEFINE group inside which a  another
+       group  named "byte" is defined. This matches an individual component of
+       an IPv4 address (a number less than 256). When  matching  takes  place,
+       this  part  of  the pattern is skipped because DEFINE acts like a false
+       condition. The rest of the pattern uses references to the  named  group
+       to  match the four dot-separated components of an IPv4 address, insist-
        ing on a word boundary at each end.
 
    Checking the PCRE2 version
 
-       Programs  that link with a PCRE2 library can check the version by call-
-       ing pcre2_config() with appropriate arguments.  Users  of  applications
-       that  do  not have access to the underlying code cannot do this. A spe-
-       cial "condition" called VERSION exists to allow such users to  discover
+       Programs that link with a PCRE2 library can check the version by  call-
+       ing  pcre2_config()  with  appropriate arguments. Users of applications
+       that do not have access to the underlying code cannot do this.  A  spe-
+       cial  "condition" called VERSION exists to allow such users to discover
        which version of PCRE2 they are dealing with by using this condition to
-       match a string such as "yesno". VERSION must be followed either by  "="
+       match  a string such as "yesno". VERSION must be followed either by "="
        or ">=" and a version number.  For example:
 
          (?(VERSION>=10.4)yes|no)
 
-       This  pattern matches "yes" if the PCRE2 version is greater or equal to
-       10.4, or "no" otherwise. The fractional part of the version number  may
+       This pattern matches "yes" if the PCRE2 version is greater or equal  to
+       10.4,  or "no" otherwise. The fractional part of the version number may
        not contain more than two digits.
 
    Assertion conditions
 
-       If  the  condition  is  not  in  any of the above formats, it must be a
-       parenthesized assertion. This may be a positive or  negative  lookahead
-       or  lookbehind  assertion. Consider this pattern, again containing non-
-       significant white space, and with the two alternatives  on  the  second
-       line:
+       If the condition is not in any of the  above  formats,  it  must  be  a
+       parenthesized  assertion.  This may be a positive or negative lookahead
+       or lookbehind assertion. However, it must be a traditional  atomic  as-
+       sertion, not one of the PCRE2-specific non-atomic assertions.
+
+       Consider  this  pattern,  again containing non-significant white space,
+       and with the two alternatives on the second line:
 
          (?(?=[^a-z]*[a-z])
          \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
 
-       The  condition  is  a  positive lookahead assertion that matches an op-
+       The condition is a positive lookahead assertion  that  matches  an  op-
        tional sequence of non-letters followed by a letter. In other words, it
        tests for the presence of at least one letter in the subject. If a let-
-       ter is found, the subject is matched  against  the  first  alternative;
-       otherwise  it  is  matched  against  the  second.  This pattern matches
-       strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
+       ter  is  found,  the  subject is matched against the first alternative;
+       otherwise it is  matched  against  the  second.  This  pattern  matches
+       strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are
        letters and dd are digits.
 
        When an assertion that is a condition contains capture groups, any cap-
-       turing that occurs in a matching branch  is  retained  afterwards,  for
-       both  positive and negative assertions, because matching always contin-
-       ues after the assertion, whether it succeeds or  fails.  (Compare  non-
-       conditional  assertions, for which captures are retained only for posi-
+       turing  that  occurs  in  a matching branch is retained afterwards, for
+       both positive and negative assertions, because matching always  contin-
+       ues  after  the  assertion, whether it succeeds or fails. (Compare non-
+       conditional assertions, for which captures are retained only for  posi-
        tive assertions that succeed.)
 
 
 COMMENTS
 
        There are two ways of including comments in patterns that are processed
-       by  PCRE2.  In  both  cases,  the start of the comment must not be in a
-       character class, nor in the middle of any  other  sequence  of  related
-       characters  such  as (?: or a group name or number. The characters that
+       by PCRE2. In both cases, the start of the comment  must  not  be  in  a
+       character  class,  nor  in  the middle of any other sequence of related
+       characters such as (?: or a group name or number. The  characters  that
        make up a comment play no part in the pattern matching.
 
-       The sequence (?# marks the start of a comment that continues up to  the
-       next  closing parenthesis. Nested parentheses are not permitted. If the
-       PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is  set,  an  unescaped  #
-       character  also  introduces  a comment, which in this case continues to
-       immediately after the next newline character or character  sequence  in
+       The  sequence (?# marks the start of a comment that continues up to the
+       next closing parenthesis. Nested parentheses are not permitted. If  the
+       PCRE2_EXTENDED  or  PCRE2_EXTENDED_MORE  option  is set, an unescaped #
+       character also introduces a comment, which in this  case  continues  to
+       immediately  after  the next newline character or character sequence in
        the pattern. Which characters are interpreted as newlines is controlled
-       by an option passed to the compiling function or by a special  sequence
+       by  an option passed to the compiling function or by a special sequence
        at the start of the pattern, as described in the section entitled "New-
        line conventions" above. Note that the end of this type of comment is a
-       literal  newline  sequence in the pattern; escape sequences that happen
+       literal newline sequence in the pattern; escape sequences  that  happen
        to represent a newline do not count. For example, consider this pattern
-       when  PCRE2_EXTENDED is set, and the default newline convention (a sin-
+       when PCRE2_EXTENDED is set, and the default newline convention (a  sin-
        gle linefeed character) is in force:
 
          abc #comment \n still comment
 
-       On encountering the # character, pcre2_compile() skips  along,  looking
-       for  a newline in the pattern. The sequence \n is still literal at this
-       stage, so it does not terminate the comment. Only an  actual  character
+       On  encountering  the # character, pcre2_compile() skips along, looking
+       for a newline in the pattern. The sequence \n is still literal at  this
+       stage,  so  it does not terminate the comment. Only an actual character
        with the code value 0x0a (the default newline) does so.
 
 
 RECURSIVE PATTERNS
 
-       Consider  the problem of matching a string in parentheses, allowing for
-       unlimited nested parentheses. Without the use of  recursion,  the  best
-       that  can  be  done  is  to use a pattern that matches up to some fixed
-       depth of nesting. It is not possible to  handle  an  arbitrary  nesting
+       Consider the problem of matching a string in parentheses, allowing  for
+       unlimited  nested  parentheses.  Without the use of recursion, the best
+       that can be done is to use a pattern that  matches  up  to  some  fixed
+       depth  of  nesting.  It  is not possible to handle an arbitrary nesting
        depth.
 
        For some time, Perl has provided a facility that allows regular expres-
-       sions to recurse (amongst other things). It does this by  interpolating
-       Perl  code in the expression at run time, and the code can refer to the
+       sions  to recurse (amongst other things). It does this by interpolating
+       Perl code in the expression at run time, and the code can refer to  the
        expression itself. A Perl pattern using code interpolation to solve the
        parentheses problem can be created like this:
 
@@ -8650,67 +8713,67 @@ RECURSIVE PATTERNS
        The (?p{...}) item interpolates Perl code at run time, and in this case
        refers recursively to the pattern in which it appears.
 
-       Obviously, PCRE2 cannot support the interpolation  of  Perl  code.  In-
-       stead,  it supports special syntax for recursion of the entire pattern,
+       Obviously,  PCRE2  cannot  support  the interpolation of Perl code. In-
+       stead, it supports special syntax for recursion of the entire  pattern,
        and also for individual capture group recursion. After its introduction
        in PCRE1 and Python, this kind of recursion was subsequently introduced
        into Perl at release 5.10.
 
-       A special item that consists of (? followed by a  number  greater  than
-       zero  and  a  closing parenthesis is a recursive subroutine call of the
-       capture group of the given number, provided that it occurs inside  that
-       group.  (If  not,  it  is a non-recursive subroutine call, which is de-
+       A  special  item  that consists of (? followed by a number greater than
+       zero and a closing parenthesis is a recursive subroutine  call  of  the
+       capture  group of the given number, provided that it occurs inside that
+       group. (If not, it is a non-recursive subroutine  call,  which  is  de-
        scribed in the next section.) The special item (?R) or (?0) is a recur-
        sive call of the entire regular expression.
 
-       This  PCRE2  pattern  solves the nested parentheses problem (assume the
+       This PCRE2 pattern solves the nested parentheses  problem  (assume  the
        PCRE2_EXTENDED option is set so that white space is ignored):
 
          \( ( [^()]++ | (?R) )* \)
 
-       First it matches an opening parenthesis. Then it matches any number  of
-       substrings  which can either be a sequence of non-parentheses, or a re-
+       First  it matches an opening parenthesis. Then it matches any number of
+       substrings which can either be a sequence of non-parentheses, or a  re-
        cursive match of the pattern itself (that is, a correctly parenthesized
-       substring).   Finally there is a closing parenthesis. Note the use of a
-       possessive quantifier to avoid  backtracking  into  sequences  of  non-
+       substring).  Finally there is a closing parenthesis. Note the use of  a
+       possessive  quantifier  to  avoid  backtracking  into sequences of non-
        parentheses.
 
-       If  this  were  part of a larger pattern, you would not want to recurse
+       If this were part of a larger pattern, you would not  want  to  recurse
        the entire pattern, so instead you could use this:
 
          ( \( ( [^()]++ | (?1) )* \) )
 
-       We have put the pattern into parentheses, and caused the  recursion  to
+       We  have  put the pattern into parentheses, and caused the recursion to
        refer to them instead of the whole pattern.
 
-       In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
-       tricky. This is made easier by the use of relative references.  Instead
+       In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
+       tricky.  This is made easier by the use of relative references. Instead
        of (?1) in the pattern above you can write (?-2) to refer to the second
-       most recently opened parentheses  preceding  the  recursion.  In  other
-       words,  a  negative  number counts capturing parentheses leftwards from
+       most  recently  opened  parentheses  preceding  the recursion. In other
+       words, a negative number counts capturing  parentheses  leftwards  from
        the point at which it is encountered.
 
-       Be aware however, that if duplicate capture group numbers are  in  use,
-       relative  references  refer  to the earliest group with the appropriate
+       Be  aware  however, that if duplicate capture group numbers are in use,
+       relative references refer to the earliest group  with  the  appropriate
        number. Consider, for example:
 
          (?|(a)|(b)) (c) (?-2)
 
        The first two capture groups (a) and (b) are both numbered 1, and group
-       (c)  is  number  2. When the reference (?-2) is encountered, the second
-       most recently opened parentheses has the number 1, but it is the  first
+       (c) is number 2. When the reference (?-2) is  encountered,  the  second
+       most  recently opened parentheses has the number 1, but it is the first
        such group (the (a) group) to which the recursion refers. This would be
-       the same if an absolute reference (?1) was used. In other words,  rela-
+       the  same if an absolute reference (?1) was used. In other words, rela-
        tive references are just a shorthand for computing a group number.
 
-       It  is  also possible to refer to subsequent capture groups, by writing
-       references such as (?+2). However, these cannot  be  recursive  because
-       the  reference  is not inside the parentheses that are referenced. They
-       are always non-recursive subroutine calls, as  described  in  the  next
+       It is also possible to refer to subsequent capture groups,  by  writing
+       references  such  as  (?+2). However, these cannot be recursive because
+       the reference is not inside the parentheses that are  referenced.  They
+       are  always  non-recursive  subroutine  calls, as described in the next
        section.
 
-       An  alternative  approach  is to use named parentheses. The Perl syntax
-       for this is (?&name); PCRE1's earlier syntax  (?P>name)  is  also  sup-
+       An alternative approach is to use named parentheses.  The  Perl  syntax
+       for  this  is  (?&name);  PCRE1's earlier syntax (?P>name) is also sup-
        ported. We could rewrite the above example as follows:
 
          (? \( ( [^()]++ | (?&pn) )* \) )
@@ -8719,57 +8782,57 @@ RECURSIVE PATTERNS
        used.
 
        The example pattern that we have been looking at contains nested unlim-
-       ited  repeats,  and  so the use of a possessive quantifier for matching
-       strings of non-parentheses is important when applying  the  pattern  to
+       ited repeats, and so the use of a possessive  quantifier  for  matching
+       strings  of  non-parentheses  is important when applying the pattern to
        strings that do not match. For example, when this pattern is applied to
 
          (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
 
-       it  yields  "no  match" quickly. However, if a possessive quantifier is
-       not used, the match runs for a very long time indeed because there  are
-       so  many  different  ways the + and * repeats can carve up the subject,
+       it yields "no match" quickly. However, if a  possessive  quantifier  is
+       not  used, the match runs for a very long time indeed because there are
+       so many different ways the + and * repeats can carve  up  the  subject,
        and all have to be tested before failure can be reported.
 
-       At the end of a match, the values of capturing  parentheses  are  those
-       from  the outermost level. If you want to obtain intermediate values, a
+       At  the  end  of a match, the values of capturing parentheses are those
+       from the outermost level. If you want to obtain intermediate values,  a
        callout function can be used (see below and the pcre2callout documenta-
        tion). If the pattern above is matched against
 
          (ab(cd)ef)
 
-       the  value  for  the  inner capturing parentheses (numbered 2) is "ef",
-       which is the last value taken on at the top level. If a  capture  group
-       is  not  matched  at  the top level, its final captured value is unset,
-       even if it was (temporarily) set at a deeper level during the  matching
+       the value for the inner capturing parentheses  (numbered  2)  is  "ef",
+       which  is  the last value taken on at the top level. If a capture group
+       is not matched at the top level, its final  captured  value  is  unset,
+       even  if it was (temporarily) set at a deeper level during the matching
        process.
 
-       Do  not  confuse  the (?R) item with the condition (R), which tests for
-       recursion.  Consider this pattern, which matches text in  angle  brack-
-       ets,  allowing for arbitrary nesting. Only digits are allowed in nested
-       brackets (that is, when recursing), whereas any characters are  permit-
+       Do not confuse the (?R) item with the condition (R),  which  tests  for
+       recursion.   Consider  this pattern, which matches text in angle brack-
+       ets, allowing for arbitrary nesting. Only digits are allowed in  nested
+       brackets  (that is, when recursing), whereas any characters are permit-
        ted at the outer level.
 
          < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
 
-       In  this  pattern,  (?(R) is the start of a conditional group, with two
-       different alternatives for the recursive and non-recursive  cases.  The
+       In this pattern, (?(R) is the start of a conditional  group,  with  two
+       different  alternatives  for the recursive and non-recursive cases. The
        (?R) item is the actual recursive call.
 
    Differences in recursion processing between PCRE2 and Perl
 
        Some former differences between PCRE2 and Perl no longer exist.
 
-       Before  release 10.30, recursion processing in PCRE2 differed from Perl
-       in that a recursive subroutine call was always  treated  as  an  atomic
-       group.  That is, once it had matched some of the subject string, it was
-       never re-entered, even if it contained untried alternatives  and  there
-       was  a  subsequent matching failure. (Historical note: PCRE implemented
+       Before release 10.30, recursion processing in PCRE2 differed from  Perl
+       in  that  a  recursive  subroutine call was always treated as an atomic
+       group. That is, once it had matched some of the subject string, it  was
+       never  re-entered,  even if it contained untried alternatives and there
+       was a subsequent matching failure. (Historical note:  PCRE  implemented
        recursion before Perl did.)
 
-       Starting with release 10.30, recursive subroutine calls are  no  longer
+       Starting  with  release 10.30, recursive subroutine calls are no longer
        treated as atomic. That is, they can be re-entered to try unused alter-
-       natives if there is a matching failure later in the  pattern.  This  is
-       now  compatible  with the way Perl works. If you want a subroutine call
+       natives  if  there  is a matching failure later in the pattern. This is
+       now compatible with the way Perl works. If you want a  subroutine  call
        to be atomic, you must explicitly enclose it in an atomic group.
 
        Supporting backtracking into recursions simplifies certain types of re-
@@ -8777,47 +8840,47 @@ RECURSIVE PATTERNS
 
          ^((.)(?1)\2|.?)$
 
-       The  second  branch  in the group matches a single central character in
-       the palindrome when there are an odd number of characters,  or  nothing
-       when  there  are  an even number of characters, but in order to work it
-       has to be able to try the second case when  the  rest  of  the  pattern
+       The second branch in the group matches a single  central  character  in
+       the  palindrome  when there are an odd number of characters, or nothing
+       when there are an even number of characters, but in order  to  work  it
+       has  to  be  able  to  try the second case when the rest of the pattern
        match fails. If you want to match typical palindromic phrases, the pat-
-       tern has to ignore all non-word characters,  which  can  be  done  like
+       tern  has  to  ignore  all  non-word characters, which can be done like
        this:
 
          ^\W*+((.)\W*+(?1)\W*+\2|\W*+.?)\W*+$
 
-       If  run  with  the  PCRE2_CASELESS option, this pattern matches phrases
-       such as "A man, a plan, a canal: Panama!". Note the use of the  posses-
-       sive  quantifier  *+  to  avoid backtracking into sequences of non-word
+       If run with the PCRE2_CASELESS option,  this  pattern  matches  phrases
+       such  as "A man, a plan, a canal: Panama!". Note the use of the posses-
+       sive quantifier *+ to avoid backtracking  into  sequences  of  non-word
        characters. Without this, PCRE2 takes a great deal longer (ten times or
-       more)  to  match typical phrases, and Perl takes so long that you think
+       more) to match typical phrases, and Perl takes so long that  you  think
        it has gone into a loop.
 
-       Another way in which PCRE2 and Perl used to differ in  their  recursion
-       processing  is  in  the  handling of captured values. Formerly in Perl,
-       when a group was called recursively or as a subroutine  (see  the  next
+       Another  way  in which PCRE2 and Perl used to differ in their recursion
+       processing is in the handling of captured  values.  Formerly  in  Perl,
+       when  a  group  was called recursively or as a subroutine (see the next
        section), it had no access to any values that were captured outside the
-       recursion, whereas in PCRE2 these values can  be  referenced.  Consider
+       recursion,  whereas  in  PCRE2 these values can be referenced. Consider
        this pattern:
 
          ^(.)(\1|a(?2))
 
-       This  pattern matches "bab". The first capturing parentheses match "b",
+       This pattern matches "bab". The first capturing parentheses match  "b",
        then in the second group, when the backreference \1 fails to match "b",
        the second alternative matches "a" and then recurses. In the recursion,
-       \1 does now match "b" and so the whole match succeeds. This match  used
+       \1  does now match "b" and so the whole match succeeds. This match used
        to fail in Perl, but in later versions (I tried 5.024) it now works.
 
 
 GROUPS AS SUBROUTINES
 
-       If  the syntax for a recursive group call (either by number or by name)
-       is used outside the parentheses to which it refers, it operates  a  bit
-       like  a  subroutine  in  a programming language. More accurately, PCRE2
+       If the syntax for a recursive group call (either by number or by  name)
+       is  used  outside the parentheses to which it refers, it operates a bit
+       like a subroutine in a programming  language.  More  accurately,  PCRE2
        treats the referenced group as an independent subpattern which it tries
-       to  match at the current matching position. The called group may be de-
-       fined before or after the reference. A numbered reference can be  abso-
+       to match at the current matching position. The called group may be  de-
+       fined  before or after the reference. A numbered reference can be abso-
        lute or relative, as in these examples:
 
          (...(absolute)...)...(?2)...
@@ -8828,106 +8891,106 @@ GROUPS AS SUBROUTINES
 
          (sens|respons)e and \1ibility
 
-       matches  "sense and sensibility" and "response and responsibility", but
+       matches "sense and sensibility" and "response and responsibility",  but
        not "sense and responsibility". If instead the pattern
 
          (sens|respons)e and (?1)ibility
 
-       is used, it does match "sense and responsibility" as well as the  other
-       two  strings.  Another  example  is  given  in the discussion of DEFINE
+       is  used, it does match "sense and responsibility" as well as the other
+       two strings. Another example is  given  in  the  discussion  of  DEFINE
        above.
 
-       Like recursions, subroutine calls used to be  treated  as  atomic,  but
-       this  changed  at  PCRE2 release 10.30, so backtracking into subroutine
-       calls can now occur. However, any capturing parentheses  that  are  set
+       Like  recursions,  subroutine  calls  used to be treated as atomic, but
+       this changed at PCRE2 release 10.30, so  backtracking  into  subroutine
+       calls  can  now  occur. However, any capturing parentheses that are set
        during the subroutine call revert to their previous values afterwards.
 
-       Processing  options such as case-independence are fixed when a group is
-       defined, so if it is used as  a  subroutine,  such  options  cannot  be
+       Processing options such as case-independence are fixed when a group  is
+       defined,  so  if  it  is  used  as a subroutine, such options cannot be
        changed for different calls. For example, consider this pattern:
 
          (abc)(?i:(?-1))
 
-       It  matches  "abcabc". It does not match "abcABC" because the change of
+       It matches "abcabc". It does not match "abcABC" because the  change  of
        processing option does not affect the called group.
 
-       The behaviour of backtracking control verbs in groups  when  called  as
+       The  behaviour  of  backtracking control verbs in groups when called as
        subroutines is described in the section entitled "Backtracking verbs in
        subroutines" below.
 
 
 ONIGURUMA SUBROUTINE SYNTAX
 
-       For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
+       For  compatibility with Oniguruma, the non-Perl syntax \g followed by a
        name or a number enclosed either in angle brackets or single quotes, is
        an alternative syntax for calling a group as a subroutine, possibly re-
-       cursively.  Here  are  two  of the examples used above, rewritten using
+       cursively. Here are two of the examples  used  above,  rewritten  using
        this syntax:
 
          (? \( ( (?>[^()]+) | \g )* \) )
          (sens|respons)e and \g'1'ibility
 
-       PCRE2 supports an extension to Oniguruma: if a number is preceded by  a
+       PCRE2  supports an extension to Oniguruma: if a number is preceded by a
        plus or a minus sign it is taken as a relative reference. For example:
 
          (abc)(?i:\g<-1>)
 
-       Note  that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
-       synonymous. The former is a backreference; the latter is  a  subroutine
+       Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are  not
+       synonymous.  The  former is a backreference; the latter is a subroutine
        call.
 
 
 CALLOUTS
 
        Perl has a feature whereby using the sequence (?{...}) causes arbitrary
-       Perl code to be obeyed in the middle of matching a regular  expression.
+       Perl  code to be obeyed in the middle of matching a regular expression.
        This makes it possible, amongst other things, to extract different sub-
        strings that match the same pair of parentheses when there is a repeti-
        tion.
 
-       PCRE2  provides  a  similar feature, but of course it cannot obey arbi-
-       trary Perl code. The feature is called "callout". The caller  of  PCRE2
-       provides  an  external  function  by putting its entry point in a match
-       context using the function pcre2_set_callout(), and then  passing  that
-       context  to  pcre2_match() or pcre2_dfa_match(). If no match context is
+       PCRE2 provides a similar feature, but of course it  cannot  obey  arbi-
+       trary  Perl  code. The feature is called "callout". The caller of PCRE2
+       provides an external function by putting its entry  point  in  a  match
+       context  using  the function pcre2_set_callout(), and then passing that
+       context to pcre2_match() or pcre2_dfa_match(). If no match  context  is
        passed, or if the callout entry point is set to NULL, callouts are dis-
        abled.
 
-       Within  a  regular expression, (?C) indicates a point at which the
-       external function is to be called. There  are  two  kinds  of  callout:
-       those  with a numerical argument and those with a string argument. (?C)
-       on its own with no argument is treated as (?C0). A  numerical  argument
-       allows  the  application  to  distinguish  between  different callouts.
-       String arguments were added for release 10.20 to make it  possible  for
-       script  languages that use PCRE2 to embed short scripts within patterns
+       Within a regular expression, (?C) indicates a point at  which  the
+       external  function  is  to  be  called. There are two kinds of callout:
+       those with a numerical argument and those with a string argument.  (?C)
+       on  its  own with no argument is treated as (?C0). A numerical argument
+       allows the  application  to  distinguish  between  different  callouts.
+       String  arguments  were added for release 10.20 to make it possible for
+       script languages that use PCRE2 to embed short scripts within  patterns
        in a similar way to Perl.
 
        During matching, when PCRE2 reaches a callout point, the external func-
-       tion  is  called.  It is provided with the number or string argument of
-       the callout, the position in the pattern, and one item of data that  is
+       tion is called. It is provided with the number or  string  argument  of
+       the  callout, the position in the pattern, and one item of data that is
        also set in the match block. The callout function may cause matching to
        proceed, to backtrack, or to fail.
 
-       By default, PCRE2 implements a  number  of  optimizations  at  matching
-       time,  and  one  side-effect is that sometimes callouts are skipped. If
-       you need all possible callouts to happen, you need to set options  that
-       disable  the relevant optimizations. More details, including a complete
-       description of the programming interface to the callout  function,  are
+       By  default,  PCRE2  implements  a  number of optimizations at matching
+       time, and one side-effect is that sometimes callouts  are  skipped.  If
+       you  need all possible callouts to happen, you need to set options that
+       disable the relevant optimizations. More details, including a  complete
+       description  of  the programming interface to the callout function, are
        given in the pcre2callout documentation.
 
    Callouts with numerical arguments
 
-       If  you  just  want  to  have  a means of identifying different callout
-       points, put a number less than 256 after the  letter  C.  For  example,
+       If you just want to have  a  means  of  identifying  different  callout
+       points,  put  a  number  less than 256 after the letter C. For example,
        this pattern has two callout points:
 
          (?C1)abc(?C2)def
 
-       If  the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical
-       callouts are automatically installed before each item in  the  pattern.
-       They  are all numbered 255. If there is a conditional group in the pat-
+       If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(),  numerical
+       callouts  are  automatically installed before each item in the pattern.
+       They are all numbered 255. If there is a conditional group in the  pat-
        tern whose condition is an assertion, an additional callout is inserted
-       just  before the condition. An explicit callout may also be set at this
+       just before the condition. An explicit callout may also be set at  this
        position, as in this example:
 
          (?(?C9)(?=a)abc|def)
@@ -8937,78 +9000,78 @@ CALLOUTS
 
    Callouts with string arguments
 
-       A  delimited  string may be used instead of a number as a callout argu-
-       ment. The starting delimiter must be one of ` ' " ^ % #  $  {  and  the
+       A delimited string may be used instead of a number as a  callout  argu-
+       ment.  The  starting  delimiter  must be one of ` ' " ^ % # $ { and the
        ending delimiter is the same as the start, except for {, where the end-
-       ing delimiter is }. If  the  ending  delimiter  is  needed  within  the
+       ing  delimiter  is  }.  If  the  ending  delimiter is needed within the
        string, it must be doubled. For example:
 
          (?C'ab ''c'' d')xyz(?C{any text})pqr
 
-       The  doubling  is  removed  before  the string is passed to the callout
+       The doubling is removed before the string  is  passed  to  the  callout
        function.
 
 
 BACKTRACKING CONTROL
 
-       There are a number of special  "Backtracking  Control  Verbs"  (to  use
-       Perl's  terminology)  that  modify the behaviour of backtracking during
-       matching. They are generally of the form (*VERB) or (*VERB:NAME).  Some
+       There  are  a  number  of  special "Backtracking Control Verbs" (to use
+       Perl's terminology) that modify the behaviour  of  backtracking  during
+       matching.  They are generally of the form (*VERB) or (*VERB:NAME). Some
        verbs take either form, and may behave differently depending on whether
-       or not a name argument is present. The names are  not  required  to  be
+       or  not  a  name  argument is present. The names are not required to be
        unique within the pattern.
 
-       By  default,  for  compatibility  with  Perl, a name is any sequence of
+       By default, for compatibility with Perl, a  name  is  any  sequence  of
        characters that does not include a closing parenthesis. The name is not
-       processed  in  any  way,  and  it  is not possible to include a closing
-       parenthesis  in  the  name.   This  can  be  changed  by  setting   the
-       PCRE2_ALT_VERBNAMES  option,  but the result is no longer Perl-compati-
+       processed in any way, and it is  not  possible  to  include  a  closing
+       parenthesis   in  the  name.   This  can  be  changed  by  setting  the
+       PCRE2_ALT_VERBNAMES option, but the result is no  longer  Perl-compati-
        ble.
 
-       When PCRE2_ALT_VERBNAMES is set, backslash  processing  is  applied  to
-       verb  names  and  only  an unescaped closing parenthesis terminates the
-       name. However, the only backslash items that are permitted are \Q,  \E,
-       and  sequences such as \x{100} that define character code points. Char-
+       When  PCRE2_ALT_VERBNAMES  is  set,  backslash processing is applied to
+       verb names and only an unescaped  closing  parenthesis  terminates  the
+       name.  However, the only backslash items that are permitted are \Q, \E,
+       and sequences such as \x{100} that define character code points.  Char-
        acter type escapes such as \d are faulted.
 
        A closing parenthesis can be included in a name either as \) or between
-       \Q  and  \E. In addition to backslash processing, if the PCRE2_EXTENDED
+       \Q and \E. In addition to backslash processing, if  the  PCRE2_EXTENDED
        or PCRE2_EXTENDED_MORE option is also set, unescaped whitespace in verb
        names is skipped, and #-comments are recognized, exactly as in the rest
-       of the pattern.  PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do  not  affect
+       of  the  pattern.  PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do not affect
        verb names unless PCRE2_ALT_VERBNAMES is also set.
 
-       The  maximum  length of a name is 255 in the 8-bit library and 65535 in
-       the 16-bit and 32-bit libraries. If the name is empty, that is, if  the
-       closing  parenthesis immediately follows the colon, the effect is as if
+       The maximum length of a name is 255 in the 8-bit library and  65535  in
+       the  16-bit and 32-bit libraries. If the name is empty, that is, if the
+       closing parenthesis immediately follows the colon, the effect is as  if
        the colon were not there. Any number of these verbs may occur in a pat-
        tern. Except for (*ACCEPT), they may not be quantified.
 
-       Since  these  verbs  are  specifically related to backtracking, most of
-       them can be used only when the pattern is to be matched using the  tra-
+       Since these verbs are specifically related  to  backtracking,  most  of
+       them  can be used only when the pattern is to be matched using the tra-
        ditional matching function, because that uses a backtracking algorithm.
-       With the exception of (*FAIL), which behaves like  a  failing  negative
+       With  the  exception  of (*FAIL), which behaves like a failing negative
        assertion, the backtracking control verbs cause an error if encountered
        by the DFA matching function.
 
-       The behaviour of these verbs in repeated  groups,  assertions,  and  in
-       capture  groups  called  as subroutines (whether or not recursively) is
+       The  behaviour  of  these  verbs in repeated groups, assertions, and in
+       capture groups called as subroutines (whether or  not  recursively)  is
        documented below.
 
    Optimizations that affect backtracking verbs
 
        PCRE2 contains some optimizations that are used to speed up matching by
        running some checks at the start of each match attempt. For example, it
-       may know the minimum length of matching subject, or that  a  particular
+       may  know  the minimum length of matching subject, or that a particular
        character must be present. When one of these optimizations bypasses the
-       running of a match,  any  included  backtracking  verbs  will  not,  of
+       running  of  a  match,  any  included  backtracking  verbs will not, of
        course, be processed. You can suppress the start-of-match optimizations
-       by setting the PCRE2_NO_START_OPTIMIZE option when  calling  pcre2_com-
-       pile(),  or by starting the pattern with (*NO_START_OPT). There is more
+       by  setting  the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com-
+       pile(), or by starting the pattern with (*NO_START_OPT). There is  more
        discussion of this option in the section entitled "Compiling a pattern"
        in the pcre2api documentation.
 
-       Experiments  with  Perl  suggest that it too has similar optimizations,
+       Experiments with Perl suggest that it too  has  similar  optimizations,
        and like PCRE2, turning them off can change the result of a match.
 
    Verbs that act immediately
@@ -9017,77 +9080,77 @@ BACKTRACKING CONTROL
 
           (*ACCEPT) or (*ACCEPT:NAME)
 
-       This verb causes the match to end successfully, skipping the  remainder
-       of  the  pattern.  However,  when  it is inside a capture group that is
+       This  verb causes the match to end successfully, skipping the remainder
+       of the pattern. However, when it is inside  a  capture  group  that  is
        called as a subroutine, only that group is ended successfully. Matching
        then continues at the outer level. If (*ACCEPT) in triggered in a posi-
-       tive assertion, the assertion succeeds; in a  negative  assertion,  the
+       tive  assertion,  the  assertion succeeds; in a negative assertion, the
        assertion fails.
 
-       If  (*ACCEPT)  is inside capturing parentheses, the data so far is cap-
+       If (*ACCEPT) is inside capturing parentheses, the data so far  is  cap-
        tured. For example:
 
          A((?:A|B(*ACCEPT)|C)D)
 
-       This matches "AB", "AAD", or "ACD"; when it matches "AB", "B"  is  cap-
+       This  matches  "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
        tured by the outer parentheses.
 
-       (*ACCEPT)  is  the only backtracking verb that is allowed to be quanti-
-       fied because an ungreedy quantification with a  minimum  of  zero  acts
+       (*ACCEPT) is the only backtracking verb that is allowed to  be  quanti-
+       fied  because  an  ungreedy  quantification with a minimum of zero acts
        only when a backtrack happens. Consider, for example,
 
          (A(*ACCEPT)??B)C
 
-       where  A,  B, and C may be complex expressions. After matching "A", the
-       matcher processes "BC"; if that fails, causing a  backtrack,  (*ACCEPT)
-       is  triggered  and the match succeeds. In both cases, all but C is cap-
-       tured. Whereas (*COMMIT) (see below) means "fail on backtrack",  a  re-
+       where A, B, and C may be complex expressions. After matching  "A",  the
+       matcher  processes  "BC"; if that fails, causing a backtrack, (*ACCEPT)
+       is triggered and the match succeeds. In both cases, all but C  is  cap-
+       tured.  Whereas  (*COMMIT) (see below) means "fail on backtrack", a re-
        peated (*ACCEPT) of this type means "succeed on backtrack".
 
-       Warning:  (*ACCEPT)  should  not be used within a script run group, be-
-       cause it causes an immediate exit from the group, bypassing the  script
+       Warning: (*ACCEPT) should not be used within a script  run  group,  be-
+       cause  it causes an immediate exit from the group, bypassing the script
        run checking.
 
          (*FAIL) or (*FAIL:NAME)
 
-       This  verb causes a matching failure, forcing backtracking to occur. It
-       may be abbreviated to (*F). It is equivalent  to  (?!)  but  easier  to
+       This verb causes a matching failure, forcing backtracking to occur.  It
+       may  be  abbreviated  to  (*F).  It is equivalent to (?!) but easier to
        read. The Perl documentation notes that it is probably useful only when
        combined with (?{}) or (??{}). Those are, of course, Perl features that
-       are  not  present  in PCRE2. The nearest equivalent is the callout fea-
+       are not present in PCRE2. The nearest equivalent is  the  callout  fea-
        ture, as for example in this pattern:
 
          a+(?C)(*FAIL)
 
-       A match with the string "aaaa" always fails, but the callout  is  taken
+       A  match  with the string "aaaa" always fails, but the callout is taken
        before each backtrack happens (in this example, 10 times).
 
-       (*ACCEPT:NAME)  and  (*FAIL:NAME)  behave the same as (*MARK:NAME)(*AC-
-       CEPT) and (*MARK:NAME)(*FAIL), respectively,  that  is,  a  (*MARK)  is
+       (*ACCEPT:NAME) and (*FAIL:NAME) behave the  same  as  (*MARK:NAME)(*AC-
+       CEPT)  and  (*MARK:NAME)(*FAIL),  respectively,  that  is, a (*MARK) is
        recorded just before the verb acts.
 
    Recording which path was taken
 
-       There  is  one  verb whose main purpose is to track how a match was ar-
-       rived at, though it also has a secondary use in  conjunction  with  ad-
+       There is one verb whose main purpose is to track how a  match  was  ar-
+       rived  at,  though  it also has a secondary use in conjunction with ad-
        vancing the match starting point (see (*SKIP) below).
 
          (*MARK:NAME) or (*:NAME)
 
-       A  name is always required with this verb. For all the other backtrack-
+       A name is always required with this verb. For all the other  backtrack-
        ing control verbs, a NAME argument is optional.
 
-       When a match succeeds, the name of the last-encountered  mark  name  on
+       When  a  match  succeeds, the name of the last-encountered mark name on
        the matching path is passed back to the caller as described in the sec-
        tion entitled "Other information about the match" in the pcre2api docu-
-       mentation.  This  applies  to all instances of (*MARK) and other verbs,
+       mentation. This applies to all instances of (*MARK)  and  other  verbs,
        including those inside assertions and atomic groups. However, there are
-       differences  in  those  cases  when (*MARK) is used in conjunction with
+       differences in those cases when (*MARK) is  used  in  conjunction  with
        (*SKIP) as described below.
 
-       The mark name that was last encountered on the matching path is  passed
-       back.  A verb without a NAME argument is ignored for this purpose. Here
-       is an example of pcre2test output, where the "mark"  modifier  requests
+       The  mark name that was last encountered on the matching path is passed
+       back. A verb without a NAME argument is ignored for this purpose.  Here
+       is  an  example of pcre2test output, where the "mark" modifier requests
        the retrieval and outputting of (*MARK) data:
 
            re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
@@ -9099,76 +9162,76 @@ BACKTRACKING CONTROL
          MK: B
 
        The (*MARK) name is tagged with "MK:" in this output, and in this exam-
-       ple it indicates which of the two alternatives matched. This is a  more
-       efficient  way of obtaining this information than putting each alterna-
+       ple  it indicates which of the two alternatives matched. This is a more
+       efficient way of obtaining this information than putting each  alterna-
        tive in its own capturing parentheses.
 
-       If a verb with a name is encountered in a positive  assertion  that  is
-       true,  the  name  is recorded and passed back if it is the last-encoun-
+       If  a  verb  with a name is encountered in a positive assertion that is
+       true, the name is recorded and passed back if it  is  the  last-encoun-
        tered. This does not happen for negative assertions or failing positive
        assertions.
 
-       After  a  partial match or a failed match, the last encountered name in
+       After a partial match or a failed match, the last encountered  name  in
        the entire match process is returned. For example:
 
            re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
          data> XP
          No match, mark = B
 
-       Note that in this unanchored example the  mark  is  retained  from  the
+       Note  that  in  this  unanchored  example the mark is retained from the
        match attempt that started at the letter "X" in the subject. Subsequent
        match attempts starting at "P" and then with an empty string do not get
        as far as the (*MARK) item, but nevertheless do not reset it.
 
-       If  you  are  interested  in  (*MARK)  values after failed matches, you
-       should probably set the PCRE2_NO_START_OPTIMIZE option (see  above)  to
+       If you are interested in  (*MARK)  values  after  failed  matches,  you
+       should  probably  set the PCRE2_NO_START_OPTIMIZE option (see above) to
        ensure that the match is always attempted.
 
    Verbs that act after backtracking
 
        The following verbs do nothing when they are encountered. Matching con-
-       tinues with what follows, but if there is a subsequent  match  failure,
-       causing  a  backtrack  to the verb, a failure is forced. That is, back-
-       tracking cannot pass to the left of the  verb.  However,  when  one  of
+       tinues  with  what follows, but if there is a subsequent match failure,
+       causing a backtrack to the verb, a failure is forced.  That  is,  back-
+       tracking  cannot  pass  to  the  left of the verb. However, when one of
        these verbs appears inside an atomic group or in a lookaround assertion
-       that is true, its effect is confined to that group,  because  once  the
-       group  has been matched, there is never any backtracking into it. Back-
+       that  is  true,  its effect is confined to that group, because once the
+       group has been matched, there is never any backtracking into it.  Back-
        tracking from beyond an assertion or an atomic group ignores the entire
        group, and seeks a preceding backtracking point.
 
-       These  verbs  differ  in exactly what kind of failure occurs when back-
-       tracking reaches them. The behaviour described below  is  what  happens
-       when  the  verb is not in a subroutine or an assertion. Subsequent sec-
+       These verbs differ in exactly what kind of failure  occurs  when  back-
+       tracking  reaches  them.  The behaviour described below is what happens
+       when the verb is not in a subroutine or an assertion.  Subsequent  sec-
        tions cover these special cases.
 
          (*COMMIT) or (*COMMIT:NAME)
 
-       This verb causes the whole match to fail outright if there is  a  later
+       This  verb  causes the whole match to fail outright if there is a later
        matching failure that causes backtracking to reach it. Even if the pat-
-       tern is unanchored, no further attempts to find a  match  by  advancing
-       the  starting  point  take place. If (*COMMIT) is the only backtracking
+       tern  is  unanchored,  no further attempts to find a match by advancing
+       the starting point take place. If (*COMMIT) is  the  only  backtracking
        verb that is encountered, once it has been passed pcre2_match() is com-
        mitted to finding a match at the current starting point, or not at all.
        For example:
 
          a+(*COMMIT)b
 
-       This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
+       This  matches  "xxaab" but not "aacaab". It can be thought of as a kind
        of dynamic anchor, or "I've started, so I must finish."
 
-       The  behaviour  of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM-
-       MIT). It is like (*MARK:NAME) in that the name is remembered for  pass-
-       ing  back  to the caller. However, (*SKIP:NAME) searches only for names
+       The behaviour of (*COMMIT:NAME) is not the same  as  (*MARK:NAME)(*COM-
+       MIT).  It is like (*MARK:NAME) in that the name is remembered for pass-
+       ing back to the caller. However, (*SKIP:NAME) searches only  for  names
        that are set with (*MARK), ignoring those set by any of the other back-
        tracking verbs.
 
-       If  there  is more than one backtracking verb in a pattern, a different
-       one that follows (*COMMIT) may be triggered first,  so  merely  passing
+       If there is more than one backtracking verb in a pattern,  a  different
+       one  that  follows  (*COMMIT) may be triggered first, so merely passing
        (*COMMIT) during a match does not always guarantee that a match must be
        at this starting point.
 
        Note that (*COMMIT) at the start of a pattern is not the same as an an-
-       chor,  unless  PCRE2's  start-of-match optimizations are turned off, as
+       chor, unless PCRE2's start-of-match optimizations are  turned  off,  as
        shown in this output from pcre2test:
 
            re> /(*COMMIT)abc/
@@ -9179,68 +9242,68 @@ BACKTRACKING CONTROL
          data> xyzabc
          No match
 
-       For the first pattern, PCRE2 knows that any match must start with  "a",
-       so  the optimization skips along the subject to "a" before applying the
-       pattern to the first set of data. The match attempt then succeeds.  The
-       second  pattern disables the optimization that skips along to the first
-       character. The pattern is now applied  starting  at  "x",  and  so  the
-       (*COMMIT)  causes  the  match to fail without trying any other starting
+       For  the first pattern, PCRE2 knows that any match must start with "a",
+       so the optimization skips along the subject to "a" before applying  the
+       pattern  to the first set of data. The match attempt then succeeds. The
+       second pattern disables the optimization that skips along to the  first
+       character.  The  pattern  is  now  applied  starting at "x", and so the
+       (*COMMIT) causes the match to fail without trying  any  other  starting
        points.
 
          (*PRUNE) or (*PRUNE:NAME)
 
-       This verb causes the match to fail at the current starting position  in
+       This  verb causes the match to fail at the current starting position in
        the subject if there is a later matching failure that causes backtrack-
-       ing to reach it. If the pattern is unanchored, the  normal  "bumpalong"
-       advance  to  the next starting character then happens. Backtracking can
-       occur as usual to the left of (*PRUNE), before it is reached,  or  when
-       matching  to  the  right  of  (*PRUNE), but if there is no match to the
-       right, backtracking cannot cross (*PRUNE). In simple cases, the use  of
-       (*PRUNE)  is just an alternative to an atomic group or possessive quan-
+       ing  to  reach it. If the pattern is unanchored, the normal "bumpalong"
+       advance to the next starting character then happens.  Backtracking  can
+       occur  as  usual to the left of (*PRUNE), before it is reached, or when
+       matching to the right of (*PRUNE), but if there  is  no  match  to  the
+       right,  backtracking cannot cross (*PRUNE). In simple cases, the use of
+       (*PRUNE) is just an alternative to an atomic group or possessive  quan-
        tifier, but there are some uses of (*PRUNE) that cannot be expressed in
-       any  other  way. In an anchored pattern (*PRUNE) has the same effect as
+       any other way. In an anchored pattern (*PRUNE) has the same  effect  as
        (*COMMIT).
 
        The behaviour of (*PRUNE:NAME) is not the same as (*MARK:NAME)(*PRUNE).
        It is like (*MARK:NAME) in that the name is remembered for passing back
-       to the caller. However, (*SKIP:NAME) searches only for names  set  with
+       to  the  caller. However, (*SKIP:NAME) searches only for names set with
        (*MARK), ignoring those set by other backtracking verbs.
 
          (*SKIP)
 
-       This  verb, when given without a name, is like (*PRUNE), except that if
-       the pattern is unanchored, the "bumpalong" advance is not to  the  next
+       This verb, when given without a name, is like (*PRUNE), except that  if
+       the  pattern  is unanchored, the "bumpalong" advance is not to the next
        character, but to the position in the subject where (*SKIP) was encoun-
-       tered. (*SKIP) signifies that whatever text was matched leading  up  to
-       it  cannot  be part of a successful match if there is a later mismatch.
+       tered.  (*SKIP)  signifies that whatever text was matched leading up to
+       it cannot be part of a successful match if there is a  later  mismatch.
        Consider:
 
          a+(*SKIP)b
 
-       If the subject is "aaaac...",  after  the  first  match  attempt  fails
-       (starting  at  the  first  character in the string), the starting point
+       If  the  subject  is  "aaaac...",  after  the first match attempt fails
+       (starting at the first character in the  string),  the  starting  point
        skips on to start the next attempt at "c". Note that a possessive quan-
-       tifer  does not have the same effect as this example; although it would
-       suppress backtracking during the first match attempt,  the  second  at-
-       tempt  would  start  at  the second character instead of skipping on to
+       tifer does not have the same effect as this example; although it  would
+       suppress  backtracking  during  the first match attempt, the second at-
+       tempt would start at the second character instead  of  skipping  on  to
        "c".
 
-       If (*SKIP) is used to specify a new starting position that is the  same
-       as  the  starting  position of the current match, or (by being inside a
-       lookbehind) earlier, the position specified by (*SKIP) is ignored,  and
+       If  (*SKIP) is used to specify a new starting position that is the same
+       as the starting position of the current match, or (by  being  inside  a
+       lookbehind)  earlier, the position specified by (*SKIP) is ignored, and
        instead the normal "bumpalong" occurs.
 
          (*SKIP:NAME)
 
-       When  (*SKIP)  has  an associated name, its behaviour is modified. When
-       such a (*SKIP) is triggered, the previous path through the  pattern  is
-       searched  for the most recent (*MARK) that has the same name. If one is
-       found, the "bumpalong" advance is to the subject position  that  corre-
-       sponds  to that (*MARK) instead of to where (*SKIP) was encountered. If
+       When (*SKIP) has an associated name, its behaviour  is  modified.  When
+       such  a  (*SKIP) is triggered, the previous path through the pattern is
+       searched for the most recent (*MARK) that has the same name. If one  is
+       found,  the  "bumpalong" advance is to the subject position that corre-
+       sponds to that (*MARK) instead of to where (*SKIP) was encountered.  If
        no (*MARK) with a matching name is found, the (*SKIP) is ignored.
 
-       The search for a (*MARK) name uses the normal  backtracking  mechanism,
-       which  means  that  it  does  not  see (*MARK) settings that are inside
+       The  search  for a (*MARK) name uses the normal backtracking mechanism,
+       which means that it does not  see  (*MARK)  settings  that  are  inside
        atomic groups or assertions, because they are never re-entered by back-
        tracking. Compare the following pcre2test examples:
 
@@ -9254,105 +9317,105 @@ BACKTRACKING CONTROL
           0: b
           1: b
 
-       In  the first example, the (*MARK) setting is in an atomic group, so it
+       In the first example, the (*MARK) setting is in an atomic group, so  it
        is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored.
-       This  allows  the second branch of the pattern to be tried at the first
-       character position.  In the second example, the (*MARK) setting is  not
-       in  an  atomic group. This allows (*SKIP:X) to find the (*MARK) when it
+       This allows the second branch of the pattern to be tried at  the  first
+       character  position.  In the second example, the (*MARK) setting is not
+       in an atomic group. This allows (*SKIP:X) to find the (*MARK)  when  it
        backtracks, and this causes a new matching attempt to start at the sec-
-       ond  character.  This  time, the (*MARK) is never seen because "a" does
+       ond character. This time, the (*MARK) is never seen  because  "a"  does
        not match "b", so the matcher immediately jumps to the second branch of
        the pattern.
 
-       Note  that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
+       Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME).  It
        ignores names that are set by other backtracking verbs.
 
          (*THEN) or (*THEN:NAME)
 
-       This verb causes a skip to the next innermost  alternative  when  back-
-       tracking  reaches  it.  That  is,  it  cancels any further backtracking
-       within the current alternative. Its name  comes  from  the  observation
+       This  verb  causes  a skip to the next innermost alternative when back-
+       tracking reaches it. That  is,  it  cancels  any  further  backtracking
+       within  the  current  alternative.  Its name comes from the observation
        that it can be used for a pattern-based if-then-else block:
 
          ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
 
-       If  the COND1 pattern matches, FOO is tried (and possibly further items
-       after the end of the group if FOO succeeds); on  failure,  the  matcher
-       skips  to  the second alternative and tries COND2, without backtracking
-       into COND1. If that succeeds and BAR fails, COND3 is tried.  If  subse-
-       quently  BAZ fails, there are no more alternatives, so there is a back-
-       track to whatever came before the entire group. If (*THEN) is  not  in-
+       If the COND1 pattern matches, FOO is tried (and possibly further  items
+       after  the  end  of the group if FOO succeeds); on failure, the matcher
+       skips to the second alternative and tries COND2,  without  backtracking
+       into  COND1.  If that succeeds and BAR fails, COND3 is tried. If subse-
+       quently BAZ fails, there are no more alternatives, so there is a  back-
+       track  to  whatever came before the entire group. If (*THEN) is not in-
        side an alternation, it acts like (*PRUNE).
 
-       The  behaviour  of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN).
+       The behaviour of (*THEN:NAME) is not the same  as  (*MARK:NAME)(*THEN).
        It is like (*MARK:NAME) in that the name is remembered for passing back
-       to  the  caller. However, (*SKIP:NAME) searches only for names set with
+       to the caller. However, (*SKIP:NAME) searches only for names  set  with
        (*MARK), ignoring those set by other backtracking verbs.
 
-       A group that does not contain a | character is just a part of  the  en-
-       closing  alternative;  it is not a nested alternation with only one al-
+       A  group  that does not contain a | character is just a part of the en-
+       closing alternative; it is not a nested alternation with only  one  al-
        ternative. The effect of (*THEN) extends beyond such a group to the en-
-       closing  alternative.  Consider this pattern, where A, B, etc. are com-
-       plex pattern fragments that do not contain any  |  characters  at  this
+       closing alternative.  Consider this pattern, where A, B, etc. are  com-
+       plex  pattern  fragments  that  do not contain any | characters at this
        level:
 
          A (B(*THEN)C) | D
 
-       If  A and B are matched, but there is a failure in C, matching does not
+       If A and B are matched, but there is a failure in C, matching does  not
        backtrack into A; instead it moves to the next alternative, that is, D.
-       However,  if  the  group containing (*THEN) is given an alternative, it
+       However, if the group containing (*THEN) is given  an  alternative,  it
        behaves differently:
 
          A (B(*THEN)C | (*FAIL)) | D
 
        The effect of (*THEN) is now confined to the inner group. After a fail-
-       ure  in  C,  matching moves to (*FAIL), which causes the whole group to
-       fail because there are no more  alternatives  to  try.  In  this  case,
+       ure in C, matching moves to (*FAIL), which causes the  whole  group  to
+       fail  because  there  are  no  more  alternatives to try. In this case,
        matching does backtrack into A.
 
-       Note  that a conditional group is not considered as having two alterna-
-       tives, because only one is ever used. In other words, the  |  character
-       in  a  conditional group has a different meaning. Ignoring white space,
+       Note that a conditional group is not considered as having two  alterna-
+       tives,  because  only one is ever used. In other words, the | character
+       in a conditional group has a different meaning. Ignoring  white  space,
        consider:
 
          ^.*? (?(?=a) a | b(*THEN)c )
 
        If the subject is "ba", this pattern does not match. Because .*? is un-
-       greedy,  it initially matches zero characters. The condition (?=a) then
-       fails, the character "b" is matched, but "c" is  not.  At  this  point,
-       matching  does  not  backtrack to .*? as might perhaps be expected from
-       the presence of the | character. The conditional group is part  of  the
-       single  alternative  that comprises the whole pattern, and so the match
-       fails. (If there was a backtrack into .*?, allowing it  to  match  "b",
+       greedy, it initially matches zero characters. The condition (?=a)  then
+       fails,  the  character  "b"  is matched, but "c" is not. At this point,
+       matching does not backtrack to .*? as might perhaps  be  expected  from
+       the  presence  of the | character. The conditional group is part of the
+       single alternative that comprises the whole pattern, and so  the  match
+       fails.  (If  there  was a backtrack into .*?, allowing it to match "b",
        the match would succeed.)
 
-       The  verbs just described provide four different "strengths" of control
+       The verbs just described provide four different "strengths" of  control
        when subsequent matching fails. (*THEN) is the weakest, carrying on the
-       match  at  the next alternative. (*PRUNE) comes next, failing the match
-       at the current starting position, but allowing an advance to  the  next
-       character  (for an unanchored pattern). (*SKIP) is similar, except that
+       match at the next alternative. (*PRUNE) comes next, failing  the  match
+       at  the  current starting position, but allowing an advance to the next
+       character (for an unanchored pattern). (*SKIP) is similar, except  that
        the advance may be more than one character. (*COMMIT) is the strongest,
        causing the entire match to fail.
 
    More than one backtracking verb
 
-       If  more  than  one  backtracking verb is present in a pattern, the one
-       that is backtracked onto first acts. For example,  consider  this  pat-
+       If more than one backtracking verb is present in  a  pattern,  the  one
+       that  is  backtracked  onto first acts. For example, consider this pat-
        tern, where A, B, etc. are complex pattern fragments:
 
          (A(*COMMIT)B(*THEN)C|ABD)
 
-       If  A matches but B fails, the backtrack to (*COMMIT) causes the entire
+       If A matches but B fails, the backtrack to (*COMMIT) causes the  entire
        match to fail. However, if A and B match, but C fails, the backtrack to
-       (*THEN)  causes  the next alternative (ABD) to be tried. This behaviour
-       is consistent, but is not always the same as Perl's. It means  that  if
-       two  or  more backtracking verbs appear in succession, all the the last
+       (*THEN) causes the next alternative (ABD) to be tried.  This  behaviour
+       is  consistent,  but is not always the same as Perl's. It means that if
+       two or more backtracking verbs appear in succession, all the  the  last
        of them has no effect. Consider this example:
 
          ...(*COMMIT)(*PRUNE)...
 
        If there is a matching failure to the right, backtracking onto (*PRUNE)
-       causes  it to be triggered, and its action is taken. There can never be
+       causes it to be triggered, and its action is taken. There can never  be
        a backtrack onto (*COMMIT).
 
    Backtracking verbs in repeated groups
@@ -9362,42 +9425,42 @@ BACKTRACKING CONTROL
 
          /(a(*COMMIT)b)+ac/
 
-       If  the  subject  is  "abac", Perl matches unless its optimizations are
-       disabled, but PCRE2 always fails because the (*COMMIT)  in  the  second
+       If the subject is "abac", Perl matches  unless  its  optimizations  are
+       disabled,  but  PCRE2  always fails because the (*COMMIT) in the second
        repeat of the group acts.
 
    Backtracking verbs in assertions
 
-       (*FAIL)  in any assertion has its normal effect: it forces an immediate
-       backtrack. The behaviour of the other  backtracking  verbs  depends  on
-       whether  or  not the assertion is standalone or acting as the condition
+       (*FAIL) in any assertion has its normal effect: it forces an  immediate
+       backtrack.  The  behaviour  of  the other backtracking verbs depends on
+       whether or not the assertion is standalone or acting as  the  condition
        in a conditional group.
 
-       (*ACCEPT) in a standalone positive assertion causes  the  assertion  to
-       succeed  without  any  further  processing; captured strings and a mark
-       name (if set) are retained. In a standalone negative  assertion,  (*AC-
+       (*ACCEPT)  in  a  standalone positive assertion causes the assertion to
+       succeed without any further processing; captured  strings  and  a  mark
+       name  (if  set) are retained. In a standalone negative assertion, (*AC-
        CEPT) causes the assertion to fail without any further processing; cap-
        tured substrings and any mark name are discarded.
 
-       If the assertion is a condition, (*ACCEPT) causes the condition  to  be
-       true  for  a  positive assertion and false for a negative one; captured
+       If  the  assertion is a condition, (*ACCEPT) causes the condition to be
+       true for a positive assertion and false for a  negative  one;  captured
        substrings are retained in both cases.
 
        The remaining verbs act only when a later failure causes a backtrack to
-       reach  them. This means that their effect is confined to the assertion,
+       reach them. This means that their effect is confined to the  assertion,
        because lookaround assertions are atomic. A backtrack that occurs after
        an assertion is complete does not jump back into the assertion. Note in
-       particular that a (*MARK) name that is  set  in  an  assertion  is  not
+       particular  that  a  (*MARK)  name  that  is set in an assertion is not
        "seen" by an instance of (*SKIP:NAME) latter in the pattern.
 
-       The  effect of (*THEN) is not allowed to escape beyond an assertion. If
-       there are no more branches to try, (*THEN) causes a positive  assertion
+       The effect of (*THEN) is not allowed to escape beyond an assertion.  If
+       there  are no more branches to try, (*THEN) causes a positive assertion
        to be false, and a negative assertion to be true.
 
-       The  other  backtracking verbs are not treated specially if they appear
-       in a standalone positive assertion. In a  conditional  positive  asser-
+       The other backtracking verbs are not treated specially if  they  appear
+       in  a  standalone  positive assertion. In a conditional positive asser-
        tion, backtracking (from within the assertion) into (*COMMIT), (*SKIP),
-       or (*PRUNE) causes the condition to be false. However, for both  stand-
+       or  (*PRUNE) causes the condition to be false. However, for both stand-
        alone and conditional negative assertions, backtracking into (*COMMIT),
        (*SKIP), or (*PRUNE) causes the assertion to be true, without consider-
        ing any further alternative branches.
@@ -9407,26 +9470,26 @@ BACKTRACKING CONTROL
        These behaviours occur whether or not the group is called recursively.
 
        (*ACCEPT) in a group called as a subroutine causes the subroutine match
-       to succeed without any further processing. Matching then continues  af-
-       ter  the  subroutine call. Perl documents this behaviour. Perl's treat-
+       to  succeed without any further processing. Matching then continues af-
+       ter the subroutine call. Perl documents this behaviour.  Perl's  treat-
        ment of the other verbs in subroutines is different in some cases.
 
-       (*FAIL) in a group called as a subroutine has  its  normal  effect:  it
+       (*FAIL)  in  a  group  called as a subroutine has its normal effect: it
        forces an immediate backtrack.
 
-       (*COMMIT),  (*SKIP),  and  (*PRUNE)  cause the subroutine match to fail
-       when triggered by being backtracked to in a group called as  a  subrou-
+       (*COMMIT), (*SKIP), and (*PRUNE) cause the  subroutine  match  to  fail
+       when  triggered  by being backtracked to in a group called as a subrou-
        tine. There is then a backtrack at the outer level.
 
        (*THEN), when triggered, skips to the next alternative in the innermost
-       enclosing group that has alternatives (its normal behaviour).  However,
+       enclosing  group that has alternatives (its normal behaviour). However,
        if there is no such group within the subroutine's group, the subroutine
        match fails and there is a backtrack at the outer level.
 
 
 SEE ALSO
 
-       pcre2api(3),   pcre2callout(3),    pcre2matching(3),    pcre2syntax(3),
+       pcre2api(3),    pcre2callout(3),    pcre2matching(3),   pcre2syntax(3),
        pcre2(3).
 
 
@@ -9439,7 +9502,7 @@ AUTHOR
 
 REVISION
 
-       Last updated: 22 June 2019
+       Last updated: 13 July 2019
        Copyright (c) 1997-2019 University of Cambridge.
 ------------------------------------------------------------------------------
  
@@ -10663,6 +10726,17 @@ LOOKAHEAD AND LOOKBEHIND ASSERTIONS
        Each top-level branch of a lookbehind must be of a fixed length.
 
 
+NON-ATOMIC LOOKAROUND ASSERTIONS
+
+       These assertions are specific to PCRE2 and are not Perl-compatible.
+
+         (*napla:...)
+         (*non_atomic_positive_lookahead:...)
+
+         (*naplb:...)
+         (*non_atomic_positive_lookbehind:...)
+
+
 SCRIPT RUNS
 
          (*script_run:...)           ) script run, can be backtracked into
@@ -10784,7 +10858,7 @@ AUTHOR
 
 REVISION
 
-       Last updated: 11 February 2019
+       Last updated: 12 July 2019
        Copyright (c) 1997-2019 University of Cambridge.
 ------------------------------------------------------------------------------
  
diff --git a/doc/pcre2compat.3 b/doc/pcre2compat.3
index 39ccc2e..59b311b 100644
--- a/doc/pcre2compat.3
+++ b/doc/pcre2compat.3
@@ -1,4 +1,4 @@
-.TH PCRE2COMPAT 3 "12 February 2019" "PCRE2 10.33"
+.TH PCRE2COMPAT 3 "13 July 2019" "PCRE2 10.34"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .SH "DIFFERENCES BETWEEN PCRE2 AND PERL"
@@ -170,6 +170,10 @@ different way and is not Perl-compatible.
 (l) PCRE2 recognizes some special sequences such as (*CR) or (*NO_JIT) at
 the start of a pattern that set overall options that cannot be changed within
 the pattern.
+.sp
+(m) PCRE2 supports non-atomic positive lookaround assertions. This is an 
+extension to the lookaround facilities. The default, Perl-compatible
+lookarounds are atomic.
 .P
 18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
 modifier restricts /i case-insensitive matching to pure ascii, ignoring Unicode
@@ -199,6 +203,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 12 February 2019
+Last updated: 13 July 2019
 Copyright (c) 1997-2019 University of Cambridge.
 .fi
diff --git a/doc/pcre2pattern.3 b/doc/pcre2pattern.3
index c0d5544..d59ac9f 100644
--- a/doc/pcre2pattern.3
+++ b/doc/pcre2pattern.3
@@ -1,4 +1,4 @@
-.TH PCRE2PATTERN 3 "22 June 2019" "PCRE2 10.34"
+.TH PCRE2PATTERN 3 "13 July 2019" "PCRE2 10.34"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .SH "PCRE2 REGULAR EXPRESSION DETAILS"
@@ -2370,9 +2370,19 @@ those that look behind it, and in each case an assertion may be positive (must
 match for the assertion to be true) or negative (must not match for the
 assertion to be true). An assertion group is matched in the normal way,
 and if it is true, matching continues after it, but with the matching position
-in the subject string is was it was before the assertion was processed.
+in the subject string reset to what it was before the assertion was processed.
 .P
-A lookaround assertion may also appear as the condition in a
+The Perl-compatible lookaround assertions are atomic. If an assertion is true,
+but there is a subsequent matching failure, there is no backtracking into the
+assertion. However, there are some cases where non-atomic assertions can be 
+useful. PCRE2 has some support for these, described in the section entitled
+.\" HTML 
+.\" 
+"Non-atomic assertions"
+.\"
+below, but they are not Perl-compatible.
+.P
+A lookaround assertion may appear as the condition in a
 .\" HTML 
 .\" 
 conditional group
@@ -2380,9 +2390,6 @@ conditional group
 (see below). In this case, the result of matching the assertion determines
 which branch of the condition is followed.
 .P
-Lookaround assertions are atomic. If an assertion is true, but there is a
-subsequent matching failure, there is no backtracking into the assertion.
-.P
 Assertion groups are not capture groups. If an assertion contains capture
 groups within it, these are counted for the purposes of numbering the capture
 groups in the whole pattern. Within each branch of an assertion, locally
@@ -2435,11 +2442,11 @@ The assertion is obeyed just once when encountered during matching.
 .SS "Alphabetic assertion names"
 .rs
 .sp
-Traditionally, symbolic sequences such as (?= and (?<= have been used to specify
-lookaround assertions. Perl 5.28 introduced some experimental alphabetic
-alternatives which might be easier to remember. They all start with (* instead
-of (? and must be written using lower case letters. PCRE2 supports the
-following synonyms:
+Traditionally, symbolic sequences such as (?= and (?<= have been used to
+specify lookaround assertions. Perl 5.28 introduced some experimental
+alphabetic alternatives which might be easier to remember. They all start with
+(* instead of (? and must be written using lower case letters. PCRE2 supports
+the following synonyms:
 .sp
   (*positive_lookahead:  or (*pla: is the same as (?=
   (*negative_lookahead:  or (*nla: is the same as (?!
@@ -2616,6 +2623,63 @@ is another pattern that matches "foo" preceded by three digits and any three
 characters that are not "999".
 .
 .
+.\" HTML 
+.SH "NON-ATOMIC ASSERTIONS"
+.rs
+.sp
+The traditional Perl-compatible lookaround assertions are atomic. That is, if
+an assertion is true, but there is a subsequent matching failure, there is no
+backtracking into the assertion. However, there are some cases where non-atomic
+positive assertions can be useful. PCRE2 provides these using the following 
+syntax:
+.sp
+  (*non_atomic_positive_lookahead:  or (*napla:
+  (*non_atomic_positive_lookbehind: or (*naplb: 
+.sp
+Consider the problem of finding the right-most word in a string that also
+appears earlier in the string, that is, it must appear at least twice in total.
+This pattern returns the required result as captured substring 1:
+.sp
+  ^(?x)(*napla: .* \eb(\ew++)) (?> .*? \eb\e1\eb ){2}
+.sp
+For a subject such as "word1 word2 word3 word2 word3 word4" the result is 
+"word3". How does it work? At the start, ^(?x) anchors the pattern and sets the 
+"x" option, which causes white space (introduced for readability) to be
+ignored. Inside the assertion, the greedy .* at first consumes the entire
+string, but then has to backtrack until the rest of the assertion can match a
+word, which is captured by group 1. In other words, when the assertion first
+succeeds, it captures the right-most word in the string.
+.P
+The current matching point is then reset to the start of the subject, and the
+rest of the pattern match checks for two occurrences of the captured word, 
+using an ungreedy .*? to scan from the left. If this succeeds, we are done, but 
+if the last word in the string does not occur twice, this part of the pattern 
+fails. If a traditional atomic lookhead (?= or (*pla: had been used, the
+assertion could not be re-entered, and the whole match would fail. The pattern
+would succeed only if the very last word in the subject was found twice.
+.P
+Using a non-atomic lookahead, however, means that when the last word does not
+occur twice in the string, the lookahead can backtrack and find the second-last
+word, and so on, until either the match succeeds, or all words have been
+tested.
+.P
+Two conditions must be met for a non-atomic assertion to be useful: the
+contents of one or more capturing groups must change after a backtrack into the
+assertion, and there must be a backreference to a changed group later in the
+pattern. If this is not the case, the rest of the pattern match fails exactly
+as before because nothing has changed, so using a non-atomic assertion just
+wastes resources.
+.P
+Non-atomic assertions are not supported by the alternative matching function
+\fBpcre2_dfa_match()\fP. They are also not supported by JIT (but may be in
+future). Note that assertions that appear as conditions for
+.\" HTML 
+.\" 
+conditional groups
+.\"
+(see below) must be atomic.
+.
+.
 .SH "SCRIPT RUNS"
 .rs
 .sp
@@ -2867,8 +2931,15 @@ than two digits.
 .sp
 If the condition is not in any of the above formats, it must be a parenthesized
 assertion. This may be a positive or negative lookahead or lookbehind
-assertion. Consider this pattern, again containing non-significant white space,
-and with the two alternatives on the second line:
+assertion. However, it must be a traditional atomic assertion, not one of the
+PCRE2-specific
+.\" HTML 
+.\" 
+non-atomic assertions.
+.\"
+.P
+Consider this pattern, again containing non-significant white space, and with
+the two alternatives on the second line:
 .sp
   (?(?=[^a-z]*[a-z])
   \ed{2}-[a-z]{3}-\ed{2}  |  \ed{2}-\ed{2}-\ed{2} )
@@ -3788,6 +3859,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 22 June 2019
+Last updated: 13 July 2019
 Copyright (c) 1997-2019 University of Cambridge.
 .fi
diff --git a/doc/pcre2syntax.3 b/doc/pcre2syntax.3
index 70538e4..f9a5fee 100644
--- a/doc/pcre2syntax.3
+++ b/doc/pcre2syntax.3
@@ -1,4 +1,4 @@
-.TH PCRE2SYNTAX 3 "11 February 2019" "PCRE2 10.33"
+.TH PCRE2SYNTAX 3 "12 July 2019" "PCRE2 10.34"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .SH "PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY"
@@ -522,6 +522,18 @@ setting with a similar syntax.
 Each top-level branch of a lookbehind must be of a fixed length.
 .
 .
+.SH "NON-ATOMIC LOOKAROUND ASSERTIONS"
+.rs
+.sp
+These assertions are specific to PCRE2 and are not Perl-compatible.
+.sp
+  (*napla:...)                  
+  (*non_atomic_positive_lookahead:...)
+.sp
+  (*naplb:...)
+  (*non_atomic_positive_lookbehind:...)
+.
+.
 .SH "SCRIPT RUNS"
 .rs
 .sp
@@ -654,6 +666,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 11 February 2019
+Last updated: 12 July 2019
 Copyright (c) 1997-2019 University of Cambridge.
 .fi
diff --git a/src/pcre2.h.in b/src/pcre2.h.in
index 78adac6..7a06aee 100644
--- a/src/pcre2.h.in
+++ b/src/pcre2.h.in
@@ -307,6 +307,7 @@ pcre2_pattern_convert(). */
 #define PCRE2_ERROR_ALPHA_ASSERTION_UNKNOWN        195
 #define PCRE2_ERROR_SCRIPT_RUN_NOT_AVAILABLE       196
 #define PCRE2_ERROR_TOO_MANY_CAPTURES              197
+#define PCRE2_ERROR_CONDITION_ATOMIC_ASSERTION_EXPECTED  198
 
 
 /* "Expected" matching error codes: no match and partial match. */
diff --git a/src/pcre2_auto_possess.c b/src/pcre2_auto_possess.c
index 6d7b7c4..3892c0d 100644
--- a/src/pcre2_auto_possess.c
+++ b/src/pcre2_auto_possess.c
@@ -624,6 +624,13 @@ for(;;)
       case OP_ASSERTBACK_NOT:
       case OP_ONCE:
       return !entered_a_group;
+      
+      /* Non-atomic assertions - don't possessify last iterator. This needs 
+      more thought. */
+      
+      case OP_ASSERT_NA:
+      case OP_ASSERTBACK_NA:
+      return FALSE;   
       }
 
     /* Skip over the bracket and inspect what comes next. */
diff --git a/src/pcre2_compile.c b/src/pcre2_compile.c
index a1af793..c50e04e 100644
--- a/src/pcre2_compile.c
+++ b/src/pcre2_compile.c
@@ -250,36 +250,41 @@ is present where expected in a conditional group. */
 #define META_LOOKBEHIND       0x80250000u  /* (?<= */
 #define META_LOOKBEHINDNOT    0x80260000u  /* (? 0 &&
             (meta < META_LOOKAHEAD || meta > META_LOOKBEHINDNOT))
           {
-          errorcode = ERR28;  /* Assertion expected */
+          errorcode = (meta == META_LOOKAHEAD_NA || meta == META_LOOKBEHIND_NA)?
+            ERR98 : ERR28;  /* (Atomic) assertion expected */
           goto FAILED;
           }
 
-        /* The lookaround alphabetic synonyms can be almost entirely handled by
-        jumping to the code that handles the traditional symbolic forms. */
+        /* The lookaround alphabetic synonyms can mostly be handled by jumping
+        to the code that handles the traditional symbolic forms. */
 
         switch(meta)
           {
@@ -3721,11 +3744,17 @@ while (ptr < ptrend)
           case META_LOOKAHEAD:
           goto POSITIVE_LOOK_AHEAD;
 
+          case META_LOOKAHEAD_NA:
+          *parsed_pattern++ = meta;
+          ptr++;
+          goto POST_ASSERTION;
+
           case META_LOOKAHEADNOT:
           goto NEGATIVE_LOOK_AHEAD;
 
           case META_LOOKBEHIND:
           case META_LOOKBEHINDNOT:
+          case META_LOOKBEHIND_NA:
           *parsed_pattern++ = meta;
           ptr--;
           goto POST_LOOKBEHIND;
@@ -4429,7 +4458,7 @@ while (ptr < ptrend)
       *parsed_pattern++ = (ptr[1] == CHAR_EQUALS_SIGN)?
         META_LOOKBEHIND : META_LOOKBEHINDNOT;
 
-      POST_LOOKBEHIND:              /* Come from (*plb: and (*nlb: */
+      POST_LOOKBEHIND:              /* Come from (*plb: (*naplb: and (*nlb: */
       *has_lookbehind = TRUE;
       offset = (PCRE2_SIZE)(ptr - cb->start_pattern - 2);
       PUTOFFSET(offset, parsed_pattern);
@@ -6300,6 +6329,11 @@ for (;; pptr++)
     cb->assert_depth += 1;
     goto GROUP_PROCESS;
 
+    case META_LOOKAHEAD_NA:
+    bravalue = OP_ASSERT_NA;
+    cb->assert_depth += 1;
+    goto GROUP_PROCESS;
+
     /* Optimize (?!) to (*FAIL) unless it is quantified - which is a weird
     thing to do, but Perl allows all assertions to be quantified, and when
     they contain capturing parentheses there may be a potential use for
@@ -6331,6 +6365,11 @@ for (;; pptr++)
     cb->assert_depth += 1;
     goto GROUP_PROCESS;
 
+    case META_LOOKBEHIND_NA:
+    bravalue = OP_ASSERTBACK_NA;
+    cb->assert_depth += 1;
+    goto GROUP_PROCESS;
+
     case META_ATOMIC:
     bravalue = OP_ONCE;
     goto GROUP_PROCESS_NOTE_EMPTY;
@@ -7931,7 +7970,10 @@ length = 2 + 2*LINK_SIZE + skipunits;
 /* Remember if this is a lookbehind assertion, and if it is, save its length
 and skip over the pattern offset. */
 
-lookbehind = *code == OP_ASSERTBACK || *code == OP_ASSERTBACK_NOT;
+lookbehind = *code == OP_ASSERTBACK || 
+             *code == OP_ASSERTBACK_NOT ||
+             *code == OP_ASSERTBACK_NA;
+
 if (lookbehind)
   {
   lookbehindlength = META_DATA(pptr[-1]);
@@ -8802,8 +8844,10 @@ for (;; pptr++)
     case META_COND_VERSION:
     case META_LOOKAHEAD:
     case META_LOOKAHEADNOT:
+    case META_LOOKAHEAD_NA:
     case META_LOOKBEHIND:
     case META_LOOKBEHINDNOT:
+    case META_LOOKBEHIND_NA:
     case META_NOCAPTURE:
     case META_SCRIPT_RUN:
     nestlevel++;
@@ -9064,6 +9108,7 @@ for (;; pptr++)
 
     case META_LOOKAHEAD:
     case META_LOOKAHEADNOT:
+    case META_LOOKAHEAD_NA:
     pptr = parsed_skip(pptr + 1, PSKIP_KET);
     if (pptr == NULL) goto PARSED_SKIP_FAILED;
 
@@ -9102,6 +9147,7 @@ for (;; pptr++)
 
     case META_LOOKBEHIND:
     case META_LOOKBEHINDNOT:
+    case META_LOOKBEHIND_NA:
     if (!set_lookbehind_lengths(&pptr, &max, errcodeptr, lcptr, recurses, cb))
       return -1;
     if (max - branchlength > extra) extra = max - branchlength;
@@ -9453,6 +9499,7 @@ for (pptr = cb->parsed_pattern; *pptr != META_END; pptr++)
     case META_KET:
     case META_LOOKAHEAD:
     case META_LOOKAHEADNOT:
+    case META_LOOKAHEAD_NA:
     case META_NOCAPTURE:
     case META_PLUS:
     case META_PLUS_PLUS:
@@ -9514,6 +9561,7 @@ for (pptr = cb->parsed_pattern; *pptr != META_END; pptr++)
 
     case META_LOOKBEHIND:
     case META_LOOKBEHINDNOT:
+    case META_LOOKBEHIND_NA:
     if (!set_lookbehind_lengths(&pptr, &max, &errorcode, &loopcount, NULL, cb))
       return errorcode;
     break;
diff --git a/src/pcre2_dfa_match.c b/src/pcre2_dfa_match.c
index 538d15d..580dbe7 100644
--- a/src/pcre2_dfa_match.c
+++ b/src/pcre2_dfa_match.c
@@ -173,6 +173,8 @@ static const uint8_t coptable[] = {
   0,                             /* Assert not                             */
   0,                             /* Assert behind                          */
   0,                             /* Assert behind not                      */
+  0,                             /* NA assert                              */
+  0,                             /* NA assert behind                       */ 
   0,                             /* ONCE                                   */
   0,                             /* SCRIPT_RUN                             */
   0, 0, 0, 0, 0,                 /* BRA, BRAPOS, CBRA, CBRAPOS, COND       */
@@ -248,6 +250,8 @@ static const uint8_t poptable[] = {
   0,                             /* Assert not                             */
   0,                             /* Assert behind                          */
   0,                             /* Assert behind not                      */
+  0,                             /* NA assert                              */
+  0,                             /* NA assert behind                       */ 
   0,                             /* ONCE                                   */
   0,                             /* SCRIPT_RUN                             */
   0, 0, 0, 0, 0,                 /* BRA, BRAPOS, CBRA, CBRAPOS, COND       */
diff --git a/src/pcre2_error.c b/src/pcre2_error.c
index 7a22384..53686ec 100644
--- a/src/pcre2_error.c
+++ b/src/pcre2_error.c
@@ -185,6 +185,7 @@ static const unsigned char compile_error_texts[] =
   "(*alpha_assertion) not recognized\0"
   "script runs require Unicode support, which this version of PCRE2 does not have\0"
   "too many capturing groups (maximum 65535)\0"
+  "atomic assertion expected after (?( or (?(?C)\0"
   ;
 
 /* Match-time and UTF error texts are in the same format. */
diff --git a/src/pcre2_internal.h b/src/pcre2_internal.h
index 5f06ac4..fe8ffe5 100644
--- a/src/pcre2_internal.h
+++ b/src/pcre2_internal.h
@@ -883,12 +883,16 @@ a positive value. */
 #define STRING_atomic0               "atomic\0"
 #define STRING_pla0                  "pla\0"
 #define STRING_plb0                  "plb\0"
+#define STRING_napla0                "napla\0"
+#define STRING_naplb0                "naplb\0"
 #define STRING_nla0                  "nla\0"
 #define STRING_nlb0                  "nlb\0"
 #define STRING_sr0                   "sr\0"
 #define STRING_asr0                  "asr\0"
 #define STRING_positive_lookahead0   "positive_lookahead\0"
 #define STRING_positive_lookbehind0  "positive_lookbehind\0"
+#define STRING_non_atomic_positive_lookahead0   "non_atomic_positive_lookahead\0"
+#define STRING_non_atomic_positive_lookbehind0  "non_atomic_positive_lookbehind\0"
 #define STRING_negative_lookahead0   "negative_lookahead\0"
 #define STRING_negative_lookbehind0  "negative_lookbehind\0"
 #define STRING_script_run0           "script_run\0"
@@ -1173,12 +1177,16 @@ only. */
 #define STRING_atomic0               STR_a STR_t STR_o STR_m STR_i STR_c "\0"
 #define STRING_pla0                  STR_p STR_l STR_a "\0"
 #define STRING_plb0                  STR_p STR_l STR_b "\0"
+#define STRING_napla0                STR_n STR_a STR_p STR_l STR_a "\0"
+#define STRING_naplb0                STR_n STR_a STR_p STR_l STR_b "\0"
 #define STRING_nla0                  STR_n STR_l STR_a "\0"
 #define STRING_nlb0                  STR_n STR_l STR_b "\0"
 #define STRING_sr0                   STR_s STR_r "\0"
 #define STRING_asr0                  STR_a STR_s STR_r "\0"
 #define STRING_positive_lookahead0   STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
 #define STRING_positive_lookbehind0  STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
+#define STRING_non_atomic_positive_lookahead0   STR_n STR_o STR_n STR_UNDERSCORE STR_a STR_t STR_o STR_m STR_i STR_c STR_UNDERSCORE STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
+#define STRING_non_atomic_positive_lookbehind0  STR_n STR_o STR_n STR_UNDERSCORE STR_a STR_t STR_o STR_m STR_i STR_c STR_UNDERSCORE STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
 #define STRING_negative_lookahead0   STR_n STR_e STR_g STR_a STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
 #define STRING_negative_lookbehind0  STR_n STR_e STR_g STR_a STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
 #define STRING_script_run0           STR_s STR_c STR_r STR_i STR_p STR_t STR_UNDERSCORE STR_r STR_u STR_n "\0"
@@ -1303,7 +1311,7 @@ enum { ESC_A = 1, ESC_G, ESC_K, ESC_B, ESC_b, ESC_D, ESC_d, ESC_S, ESC_s,
 Starting from 1 (i.e. after OP_END), the values up to OP_EOD must correspond in
 order to the list of escapes immediately above. Furthermore, values up to
 OP_DOLLM must not be changed without adjusting the table called autoposstab in
-pcre2_auto_possess.c
+pcre2_auto_possess.c.
 
 Whenever this list is updated, the two macro definitions that follow must be
 updated to match. The possessification table called "opcode_possessify" in
@@ -1501,80 +1509,81 @@ enum {
   OP_KETRMIN,        /* 123 order. They are for groups the repeat for ever. */
   OP_KETRPOS,        /* 124 Possessive unlimited repeat. */
 
-  /* The assertions must come before BRA, CBRA, ONCE, and COND, and the four
-  asserts must remain in order. */
+  /* The assertions must come before BRA, CBRA, ONCE, and COND. */
 
   OP_REVERSE,        /* 125 Move pointer back - used in lookbehind assertions */
   OP_ASSERT,         /* 126 Positive lookahead */
   OP_ASSERT_NOT,     /* 127 Negative lookahead */
   OP_ASSERTBACK,     /* 128 Positive lookbehind */
   OP_ASSERTBACK_NOT, /* 129 Negative lookbehind */
+  OP_ASSERT_NA,      /* 130 Positive non-atomic lookahead */
+  OP_ASSERTBACK_NA,  /* 131 Positive non-atomic lookbehind */
 
   /* ONCE, SCRIPT_RUN, BRA, BRAPOS, CBRA, CBRAPOS, and COND must come
   immediately after the assertions, with ONCE first, as there's a test for >=
   ONCE for a subpattern that isn't an assertion. The POS versions must
   immediately follow the non-POS versions in each case. */
 
-  OP_ONCE,           /* 130 Atomic group, contains captures */
-  OP_SCRIPT_RUN,     /* 131 Non-capture, but check characters' scripts */
-  OP_BRA,            /* 132 Start of non-capturing bracket */
-  OP_BRAPOS,         /* 133 Ditto, with unlimited, possessive repeat */
-  OP_CBRA,           /* 134 Start of capturing bracket */
-  OP_CBRAPOS,        /* 135 Ditto, with unlimited, possessive repeat */
-  OP_COND,           /* 136 Conditional group */
+  OP_ONCE,           /* 132 Atomic group, contains captures */
+  OP_SCRIPT_RUN,     /* 133 Non-capture, but check characters' scripts */
+  OP_BRA,            /* 134 Start of non-capturing bracket */
+  OP_BRAPOS,         /* 135 Ditto, with unlimited, possessive repeat */
+  OP_CBRA,           /* 136 Start of capturing bracket */
+  OP_CBRAPOS,        /* 137 Ditto, with unlimited, possessive repeat */
+  OP_COND,           /* 138 Conditional group */
 
   /* These five must follow the previous five, in the same order. There's a
   check for >= SBRA to distinguish the two sets. */
 
-  OP_SBRA,           /* 137 Start of non-capturing bracket, check empty  */
-  OP_SBRAPOS,        /* 138 Ditto, with unlimited, possessive repeat */
-  OP_SCBRA,          /* 139 Start of capturing bracket, check empty */
-  OP_SCBRAPOS,       /* 140 Ditto, with unlimited, possessive repeat */
-  OP_SCOND,          /* 141 Conditional group, check empty */
+  OP_SBRA,           /* 139 Start of non-capturing bracket, check empty  */
+  OP_SBRAPOS,        /* 149 Ditto, with unlimited, possessive repeat */
+  OP_SCBRA,          /* 141 Start of capturing bracket, check empty */
+  OP_SCBRAPOS,       /* 142 Ditto, with unlimited, possessive repeat */
+  OP_SCOND,          /* 143 Conditional group, check empty */
 
   /* The next two pairs must (respectively) be kept together. */
 
-  OP_CREF,           /* 142 Used to hold a capture number as condition */
-  OP_DNCREF,         /* 143 Used to point to duplicate names as a condition */
-  OP_RREF,           /* 144 Used to hold a recursion number as condition */
-  OP_DNRREF,         /* 145 Used to point to duplicate names as a condition */
-  OP_FALSE,          /* 146 Always false (used by DEFINE and VERSION) */
-  OP_TRUE,           /* 147 Always true (used by VERSION) */
+  OP_CREF,           /* 144 Used to hold a capture number as condition */
+  OP_DNCREF,         /* 145 Used to point to duplicate names as a condition */
+  OP_RREF,           /* 146 Used to hold a recursion number as condition */
+  OP_DNRREF,         /* 147 Used to point to duplicate names as a condition */
+  OP_FALSE,          /* 148 Always false (used by DEFINE and VERSION) */
+  OP_TRUE,           /* 149 Always true (used by VERSION) */
 
-  OP_BRAZERO,        /* 148 These two must remain together and in this */
-  OP_BRAMINZERO,     /* 149 order. */
-  OP_BRAPOSZERO,     /* 150 */
+  OP_BRAZERO,        /* 150 These two must remain together and in this */
+  OP_BRAMINZERO,     /* 151 order. */
+  OP_BRAPOSZERO,     /* 152 */
 
   /* These are backtracking control verbs */
 
-  OP_MARK,           /* 151 always has an argument */
-  OP_PRUNE,          /* 152 */
-  OP_PRUNE_ARG,      /* 153 same, but with argument */
-  OP_SKIP,           /* 154 */
-  OP_SKIP_ARG,       /* 155 same, but with argument */
-  OP_THEN,           /* 156 */
-  OP_THEN_ARG,       /* 157 same, but with argument */
-  OP_COMMIT,         /* 158 */
-  OP_COMMIT_ARG,     /* 159 same, but with argument */
+  OP_MARK,           /* 153 always has an argument */
+  OP_PRUNE,          /* 154 */
+  OP_PRUNE_ARG,      /* 155 same, but with argument */
+  OP_SKIP,           /* 156 */
+  OP_SKIP_ARG,       /* 157 same, but with argument */
+  OP_THEN,           /* 158 */
+  OP_THEN_ARG,       /* 159 same, but with argument */
+  OP_COMMIT,         /* 160 */
+  OP_COMMIT_ARG,     /* 161 same, but with argument */
 
   /* These are forced failure and success verbs. FAIL and ACCEPT do accept an
   argument, but these cases can be compiled as, for example, (*MARK:X)(*FAIL)
   without the need for a special opcode. */
 
-  OP_FAIL,           /* 160 */
-  OP_ACCEPT,         /* 161 */
-  OP_ASSERT_ACCEPT,  /* 162 Used inside assertions */
-  OP_CLOSE,          /* 163 Used before OP_ACCEPT to close open captures */
+  OP_FAIL,           /* 162 */
+  OP_ACCEPT,         /* 163 */
+  OP_ASSERT_ACCEPT,  /* 164 Used inside assertions */
+  OP_CLOSE,          /* 165 Used before OP_ACCEPT to close open captures */
 
   /* This is used to skip a subpattern with a {0} quantifier */
 
-  OP_SKIPZERO,       /* 164 */
+  OP_SKIPZERO,       /* 166 */
 
   /* This is used to identify a DEFINE group during compilation so that it can
   be checked for having only one branch. It is changed to OP_FALSE before
   compilation finishes. */
 
-  OP_DEFINE,         /* 165 */
+  OP_DEFINE,         /* 167 */
 
   /* This is not an opcode, but is used to check that tables indexed by opcode
   are the correct length, in order to catch updating errors - there have been
@@ -1587,7 +1596,7 @@ enum {
 /* *** NOTE NOTE NOTE *** Whenever the list above is updated, the two macro
 definitions that follow must also be updated to match. There are also tables
 called "opcode_possessify" in pcre2_compile.c and "coptable" and "poptable" in
-pcre2_dfa_exec.c that must be updated. */
+pcre2_dfa_match.c that must be updated. */
 
 
 /* This macro defines textual names for all the opcodes. These are used only
@@ -1620,7 +1629,9 @@ some cases doesn't actually use these names at all). */
   "class", "nclass", "xclass", "Ref", "Refi", "DnRef", "DnRefi",  \
   "Recurse", "Callout", "CalloutStr",                             \
   "Alt", "Ket", "KetRmax", "KetRmin", "KetRpos",                  \
-  "Reverse", "Assert", "Assert not", "AssertB", "AssertB not",    \
+  "Reverse", "Assert", "Assert not",                              \
+  "Assert back", "Assert back not",                               \
+  "Non-atomic assert", "Non-atomic assert back",                  \
   "Once",                                                         \
   "Script run",                                                   \
   "Bra", "BraPos", "CBra", "CBraPos",                             \
@@ -1705,6 +1716,8 @@ in UTF-8 mode. The code that uses this table must know about such things. */
   1+LINK_SIZE,                   /* Assert not                             */ \
   1+LINK_SIZE,                   /* Assert behind                          */ \
   1+LINK_SIZE,                   /* Assert behind not                      */ \
+  1+LINK_SIZE,                   /* NA Assert                              */ \
+  1+LINK_SIZE,                   /* NA Assert behind                       */ \
   1+LINK_SIZE,                   /* ONCE                                   */ \
   1+LINK_SIZE,                   /* SCRIPT_RUN                             */ \
   1+LINK_SIZE,                   /* BRA                                    */ \
diff --git a/src/pcre2_match.c b/src/pcre2_match.c
index c7730a2..80220d3 100644
--- a/src/pcre2_match.c
+++ b/src/pcre2_match.c
@@ -5127,6 +5127,8 @@ fprintf(stderr, "++ op=%d\n", *Fecode);
 
     case OP_ASSERT:
     case OP_ASSERTBACK:
+    case OP_ASSERT_NA:
+    case OP_ASSERTBACK_NA:
     Lframe_type = GF_NOCAPTURE | Fop;
     for (;;)
       {
@@ -5497,10 +5499,20 @@ fprintf(stderr, "++ op=%d\n", *Fecode);
       case OP_SCOND:
       break;
 
-      /* Positive assertions are like OP_ONCE, except that in addition the
+      /* Non-atomic positive assertions are like OP_BRA, except that the
       subject pointer must be put back to where it was at the start of the
       assertion. */
 
+      case OP_ASSERT_NA:
+      case OP_ASSERTBACK_NA:
+      if (Feptr > mb->last_used_ptr) mb->last_used_ptr = Feptr;
+      Feptr = P->eptr;
+      break;
+
+      /* Atomic positive assertions are like OP_ONCE, except that in addition
+      the subject pointer must be put back to where it was at the start of the
+      assertion. */
+
       case OP_ASSERT:
       case OP_ASSERTBACK:
       if (Feptr > mb->last_used_ptr) mb->last_used_ptr = Feptr;
diff --git a/src/pcre2_printint.c b/src/pcre2_printint.c
index b132d44..87b063f 100644
--- a/src/pcre2_printint.c
+++ b/src/pcre2_printint.c
@@ -392,6 +392,8 @@ for(;;)
     case OP_ASSERT_NOT:
     case OP_ASSERTBACK:
     case OP_ASSERTBACK_NOT:
+    case OP_ASSERT_NA:
+    case OP_ASSERTBACK_NA:  
     case OP_ONCE:
     case OP_SCRIPT_RUN:
     case OP_COND:
diff --git a/src/pcre2_study.c b/src/pcre2_study.c
index a2f1af5..3fe2997 100644
--- a/src/pcre2_study.c
+++ b/src/pcre2_study.c
@@ -240,6 +240,8 @@ for (;;)
     case OP_ASSERT_NOT:
     case OP_ASSERTBACK:
     case OP_ASSERTBACK_NOT:
+    case OP_ASSERT_NA:
+    case OP_ASSERTBACK_NA:  
     do cc += GET(cc, 1); while (*cc == OP_ALT);
     /* Fall through */
 
@@ -1089,6 +1091,7 @@ do
       case OP_ONCE:
       case OP_SCRIPT_RUN:
       case OP_ASSERT:
+      case OP_ASSERT_NA: 
       rc = set_start_bits(re, tcode, utf);
       if (rc == SSB_FAIL || rc == SSB_UNKNOWN) return rc;
       if (rc == SSB_DONE) try_next = FALSE; else
@@ -1131,6 +1134,7 @@ do
       case OP_ASSERT_NOT:
       case OP_ASSERTBACK:
       case OP_ASSERTBACK_NOT:
+      case OP_ASSERTBACK_NA: 
       do tcode += GET(tcode, 1); while (*tcode == OP_ALT);
       tcode += 1 + LINK_SIZE;
       break;
diff --git a/testdata/testinput2 b/testdata/testinput2
index a38c3b2..a6c11dd 100644
--- a/testdata/testinput2
+++ b/testdata/testinput2
@@ -5653,4 +5653,33 @@ a)"xI
 # Multiplication overflow
 /(X{65535})(?<=\1{32770})/
 
+# ---- Non-atomic assertion tests ----
+
+# Expect error: not allowed as a condition
+/(?(*napla:xx)bc)/
+
+/\A(*pla:.*\b(\w++))(?>.*?\b\1\b){3}/
+    word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+
+/\A(*napla:.*\b(\w++))(?>.*?\b\1\b){3}/
+    word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+
+/(*plb:(.)..|(.)...)(\1|\2)/
+    abcdb\=offset=4 
+    abcda\=offset=4 
+
+/(*naplb:(.)..|(.)...)(\1|\2)/
+    abcdb\=offset=4 
+    abcda\=offset=4 
+    
+/(*non_atomic_positive_lookahead:ab)/B
+ 
+/(*non_atomic_positive_lookbehind:ab)/B 
+
+/(*pla:ab+)/B
+
+/(*napla:ab+)/B
+
+# ----
+
 # End of testinput2
diff --git a/testdata/testoutput2 b/testdata/testoutput2
index b5e44f5..32be71d 100644
--- a/testdata/testoutput2
+++ b/testdata/testoutput2
@@ -11117,7 +11117,7 @@ Matched, but too many substrings
 ------------------------------------------------------------------
         Bra
         Brazero
-        AssertB
+        Assert back
         Reverse
         CBra 1
         abc
@@ -13346,7 +13346,7 @@ Failed: error 144 at offset 5: subpattern name must start with a non-digit
         Ket
         red
         \b
-        AssertB
+        Assert back
         Reverse
         \w
         Ket
@@ -13403,7 +13403,7 @@ Failed: error 133 at offset 7: parentheses are too deeply nested (stack check)
         Once
         \s*+
         Ket
-        AssertB
+        Assert back
         Reverse
         \w
         Ket
@@ -16619,7 +16619,7 @@ No match
 /(?<=(?=.){4,5}x)/B
 ------------------------------------------------------------------
         Bra
-        AssertB
+        Assert back
         Reverse
         Assert
         Any
@@ -17086,6 +17086,87 @@ Failed: error 187 at offset 15: lookbehind assertion is too long
 /(X{65535})(?<=\1{32770})/
 Failed: error 187 at offset 10: lookbehind assertion is too long
 
+# ---- Non-atomic assertion tests ----
+
+# Expect error: not allowed as a condition
+/(?(*napla:xx)bc)/
+Failed: error 198 at offset 9: atomic assertion expected after (?( or (?(?C)
+
+/\A(*pla:.*\b(\w++))(?>.*?\b\1\b){3}/
+    word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+No match
+
+/\A(*napla:.*\b(\w++))(?>.*?\b\1\b){3}/
+    word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+ 0: word1 word3 word1 word2 word3 word2 word2 word1 word3
+ 1: word3
+
+/(*plb:(.)..|(.)...)(\1|\2)/
+    abcdb\=offset=4 
+ 0: b
+ 1: b
+ 2: 
+ 3: b
+    abcda\=offset=4 
+No match
+
+/(*naplb:(.)..|(.)...)(\1|\2)/
+    abcdb\=offset=4 
+ 0: b
+ 1: b
+ 2: 
+ 3: b
+    abcda\=offset=4 
+ 0: a
+ 1: 
+ 2: a
+ 3: a
+    
+/(*non_atomic_positive_lookahead:ab)/B
+------------------------------------------------------------------
+        Bra
+        Non-atomic assert
+        ab
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+ 
+/(*non_atomic_positive_lookbehind:ab)/B 
+------------------------------------------------------------------
+        Bra
+        Non-atomic assert back
+        Reverse
+        ab
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+
+/(*pla:ab+)/B
+------------------------------------------------------------------
+        Bra
+        Assert
+        a
+        b++
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+
+/(*napla:ab+)/B
+------------------------------------------------------------------
+        Bra
+        Non-atomic assert
+        a
+        b+
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+
+# ----
+
 # End of testinput2
 Error -70: PCRE2_ERROR_BADDATA (unknown error number)
 Error -62: bad serialized data
diff --git a/testdata/testoutput5 b/testdata/testoutput5
index 4249c5e..cc25dcc 100644
--- a/testdata/testoutput5
+++ b/testdata/testoutput5
@@ -4017,7 +4017,7 @@ MK: a\x{12345}b\x{09}(d)c
 ------------------------------------------------------------------
         Bra
         \b
-        AssertB
+        Assert back
         Reverse
         prop Xwd
         Ket
@@ -4196,7 +4196,7 @@ Failed: error 125 at offset 2: lookbehind assertion is not fixed length
 ------------------------------------------------------------------
         Bra
         ^
-        AssertB not
+        Assert back not
         Assert
         \x{10385c}
         Ket
@@ -4828,7 +4828,7 @@ MK: ABC
 /(?