3 perlreapi - Perl regular expression plugin interface
7 As of Perl 5.9.5 there is a new interface for plugging and using
8 regular expression engines other than the default one.
10 Each engine is supposed to provide access to a constant structure of the
13 typedef struct regexp_engine {
14 REGEXP* (*comp) (pTHX_
15 const SV * const pattern, const U32 flags);
19 char* strend, char* strbeg,
20 I32 minend, SV* screamer,
21 void* data, U32 flags);
22 char* (*intuit) (pTHX_
23 REGEXP * const rx, SV *sv,
24 char *strpos, char *strend, U32 flags,
25 struct re_scream_pos_data_s *data);
26 SV* (*checkstr) (pTHX_ REGEXP * const rx);
27 void (*free) (pTHX_ REGEXP * const rx);
28 void (*numbered_buff_FETCH) (pTHX_
32 void (*numbered_buff_STORE) (pTHX_
35 SV const * const value);
36 I32 (*numbered_buff_LENGTH) (pTHX_
40 SV* (*named_buff) (pTHX_
45 SV* (*named_buff_iter) (pTHX_
47 const SV * const lastkey,
49 SV* (*qr_package)(pTHX_ REGEXP * const rx);
51 void* (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
53 REGEXP* (*op_comp) (...);
56 When a regexp is compiled, its C<engine> field is then set to point at
57 the appropriate structure, so that when it needs to be used Perl can find
58 the right routines to do so.
60 In order to install a new regexp handler, C<$^H{regcomp}> is set
61 to an integer which (when casted appropriately) resolves to one of these
62 structures. When compiling, the C<comp> method is executed, and the
63 resulting C<regexp> structure's engine field is expected to point back at
66 The pTHX_ symbol in the definition is a macro used by Perl under threading
67 to provide an extra argument to the routine holding a pointer back to
68 the interpreter that is executing the regexp. So under threading all
69 routines get an extra argument.
75 REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags);
77 Compile the pattern stored in C<pattern> using the given C<flags> and
78 return a pointer to a prepared C<REGEXP> structure that can perform
79 the match. See L</The REGEXP structure> below for an explanation of
80 the individual fields in the REGEXP struct.
82 The C<pattern> parameter is the scalar that was used as the
83 pattern. Previous versions of Perl would pass two C<char*> indicating
84 the start and end of the stringified pattern; the following snippet can
85 be used to get the old parameters:
88 char* exp = SvPV(pattern, plen);
89 char* xend = exp + plen;
91 Since any scalar can be passed as a pattern, it's possible to implement
92 an engine that does something with an array (C<< "ook" =~ [ qw/ eek
93 hlagh / ] >>) or with the non-stringified form of a compiled regular
94 expression (C<< "ook" =~ qr/eek/ >>). Perl's own engine will always
95 stringify everything using the snippet above, but that doesn't mean
96 other engines have to.
98 The C<flags> parameter is a bitfield which indicates which of the
99 C<msixp> flags the regex was compiled with. It also contains
100 additional info, such as if C<use locale> is in effect.
102 The C<eogc> flags are stripped out before being passed to the comp
103 routine. The regex engine does not need to know if any of these
104 are set, as those flags should only affect what Perl does with the
105 pattern and its match variables, not how it gets compiled and
108 By the time the comp callback is called, some of these flags have
109 already had effect (noted below where applicable). However most of
110 their effect occurs after the comp callback has run, in routines that
111 read the C<< rx->extflags >> field which it populates.
113 In general the flags should be preserved in C<< rx->extflags >> after
114 compilation, although the regex engine might want to add or delete
115 some of them to invoke or disable some special behavior in Perl. The
116 flags along with any special behavior they cause are documented below:
118 The pattern modifiers:
122 =item C</m> - RXf_PMf_MULTILINE
124 If this is in C<< rx->extflags >> it will be passed to
125 C<Perl_fbm_instr> by C<pp_split> which will treat the subject string
126 as a multi-line string.
128 =item C</s> - RXf_PMf_SINGLELINE
130 =item C</i> - RXf_PMf_FOLD
132 =item C</x> - RXf_PMf_EXTENDED
134 If present on a regex, C<"#"> comments will be handled differently by the
135 tokenizer in some cases.
137 TODO: Document those cases.
139 =item C</p> - RXf_PMf_KEEPCOPY
145 The character set semantics are determined by an enum that is contained
146 in this field. This is still experimental and subject to change, but
147 the current interface returns the rules by use of the in-line function
148 C<get_regex_charset(const U32 flags)>. The only currently documented
149 value returned from it is REGEX_LOCALE_CHARSET, which is set if
150 C<use locale> is in effect. If present in C<< rx->extflags >>,
151 C<split> will use the locale dependent definition of whitespace
152 when RXf_SKIPWHITE or RXf_WHITE is in effect. ASCII whitespace
153 is defined as per L<isSPACE|perlapi/isSPACE>, and by the internal
154 macros C<is_utf8_space> under UTF-8, and C<isSPACE_LC> under C<use
165 This flag was removed in perl 5.18.0. C<split ' '> is now special-cased
166 solely in the parser. RXf_SPLIT is still #defined, so you can test for it.
167 This is how it used to work:
169 If C<split> is invoked as C<split ' '> or with no arguments (which
170 really means C<split(' ', $_)>, see L<split|perlfunc/split>), Perl will
171 set this flag. The regex engine can then check for it and set the
172 SKIPWHITE and WHITE extflags. To do this, the Perl engine does:
174 if (flags & RXf_SPLIT && r->prelen == 1 && r->precomp[0] == ' ')
175 r->extflags |= (RXf_SKIPWHITE|RXf_WHITE);
179 These flags can be set during compilation to enable optimizations in
180 the C<split> operator.
186 This flag was removed in perl 5.18.0. It is still #defined, so you can
187 set it, but doing so will have no effect. This is how it used to work:
189 If the flag is present in C<< rx->extflags >> C<split> will delete
190 whitespace from the start of the subject string before it's operated
191 on. What is considered whitespace depends on if the subject is a
192 UTF-8 string and if the C<RXf_PMf_LOCALE> flag is set.
194 If RXf_WHITE is set in addition to this flag, C<split> will behave like
195 C<split " "> under the Perl engine.
199 Tells the split operator to split the target string on newlines
200 (C<\n>) without invoking the regex engine.
202 Perl's engine sets this if the pattern is C</^/> (C<plen == 1 && *exp
203 == '^'>), even under C</^/s>; see L<split|perlfunc>. Of course a
204 different regex engine might want to use the same optimizations
205 with a different syntax.
209 Tells the split operator to split the target string on whitespace
210 without invoking the regex engine. The definition of whitespace varies
211 depending on if the target string is a UTF-8 string and on
212 if RXf_PMf_LOCALE is set.
214 Perl's engine sets this flag if the pattern is C<\s+>.
218 Tells the split operator to split the target string on
219 characters. The definition of character varies depending on if
220 the target string is a UTF-8 string.
222 Perl's engine sets this flag on empty patterns, this optimization
223 makes C<split //> much faster than it would otherwise be. It's even
224 faster than C<unpack>.
226 =item RXf_MODIFIES_VARS
228 Added in perl 5.18.0, this flag indicates that a regular expression might
229 assign to non-magical variables (such as $REGMARK and $REGERROR) during
230 matching. C<s///> will skip certain optimisations when this is set.
236 I32 exec(pTHX_ REGEXP * const rx,
237 char *stringarg, char* strend, char* strbeg,
238 I32 minend, SV* screamer,
239 void* data, U32 flags);
241 Execute a regexp. The arguments are
247 The regular expression to execute.
251 This strangely-named arg is the SV to be matched against. Note that the
252 actual char array to be matched against is supplied by the arguments
253 described below; the SV is just used to determine UTF8ness, C<pos()> etc.
257 Pointer to the physical start of the string.
261 Pointer to the character following the physical end of the string (i.e.
266 Pointer to the position in the string where matching should start; it might
267 not be equal to C<strbeg> (for example in a later iteration of C</.../g>).
271 Minimum length of string (measured in bytes from C<stringarg>) that must
272 match; if the engine reaches the end of the match but hasn't reached this
273 position in the string, it should fail.
277 Optimisation data; subject to change.
281 Optimisation flags; subject to change.
287 char* intuit(pTHX_ REGEXP * const rx,
288 SV *sv, char *strpos, char *strend,
289 const U32 flags, struct re_scream_pos_data_s *data);
291 Find the start position where a regex match should be attempted,
292 or possibly if the regex engine should not be run because the
293 pattern can't match. This is called, as appropriate, by the core,
294 depending on the values of the C<extflags> member of the C<regexp>
299 SV* checkstr(pTHX_ REGEXP * const rx);
301 Return a SV containing a string that must appear in the pattern. Used
302 by C<split> for optimising matches.
306 void free(pTHX_ REGEXP * const rx);
308 Called by Perl when it is freeing a regexp pattern so that the engine
309 can release any resources pointed to by the C<pprivate> member of the
310 C<regexp> structure. This is only responsible for freeing private data;
311 Perl will handle releasing anything else contained in the C<regexp> structure.
313 =head2 Numbered capture callbacks
315 Called to get/set the value of C<$`>, C<$'>, C<$&> and their named
316 equivalents, ${^PREMATCH}, ${^POSTMATCH} and $^{MATCH}, as well as the
317 numbered capture groups (C<$1>, C<$2>, ...).
319 The C<paren> parameter will be C<1> for C<$1>, C<2> for C<$2> and so
320 forth, and have these symbolic values for the special variables:
322 ${^PREMATCH} RX_BUFF_IDX_CARET_PREMATCH
323 ${^POSTMATCH} RX_BUFF_IDX_CARET_POSTMATCH
324 ${^MATCH} RX_BUFF_IDX_CARET_FULLMATCH
325 $` RX_BUFF_IDX_PREMATCH
326 $' RX_BUFF_IDX_POSTMATCH
327 $& RX_BUFF_IDX_FULLMATCH
329 Note that in Perl 5.17.3 and earlier, the last three constants were also
330 used for the caret variants of the variables.
333 The names have been chosen by analogy with L<Tie::Scalar> methods
334 names with an additional B<LENGTH> callback for efficiency. However
335 named capture variables are currently not tied internally but
336 implemented via magic.
338 =head3 numbered_buff_FETCH
340 void numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren,
343 Fetch a specified numbered capture. C<sv> should be set to the scalar
344 to return, the scalar is passed as an argument rather than being
345 returned from the function because when it's called Perl already has a
346 scalar to store the value, creating another one would be
347 redundant. The scalar can be set with C<sv_setsv>, C<sv_setpvn> and
348 friends, see L<perlapi>.
350 This callback is where Perl untaints its own capture variables under
351 taint mode (see L<perlsec>). See the C<Perl_reg_numbered_buff_fetch>
352 function in F<regcomp.c> for how to untaint capture variables if
353 that's something you'd like your engine to do as well.
355 =head3 numbered_buff_STORE
357 void (*numbered_buff_STORE) (pTHX_
360 SV const * const value);
362 Set the value of a numbered capture variable. C<value> is the scalar
363 that is to be used as the new value. It's up to the engine to make
364 sure this is used as the new value (or reject it).
368 if ("ook" =~ /(o*)/) {
369 # 'paren' will be '1' and 'value' will be 'ee'
373 Perl's own engine will croak on any attempt to modify the capture
374 variables, to do this in another engine use the following callback
375 (copied from C<Perl_reg_numbered_buff_store>):
378 Example_reg_numbered_buff_store(pTHX_
381 SV const * const value)
384 PERL_UNUSED_ARG(paren);
385 PERL_UNUSED_ARG(value);
388 Perl_croak(aTHX_ PL_no_modify);
391 Actually Perl will not I<always> croak in a statement that looks
392 like it would modify a numbered capture variable. This is because the
393 STORE callback will not be called if Perl can determine that it
394 doesn't have to modify the value. This is exactly how tied variables
395 behave in the same situation:
398 use base 'Tie::Scalar';
400 sub TIESCALAR { bless [] }
402 sub STORE { die "This doesn't get called" }
406 tie my $sv => "CaptureVar";
409 Because C<$sv> is C<undef> when the C<y///> operator is applied to it,
410 the transliteration won't actually execute and the program won't
411 C<die>. This is different to how 5.8 and earlier versions behaved
412 since the capture variables were READONLY variables then; now they'll
413 just die when assigned to in the default engine.
415 =head3 numbered_buff_LENGTH
417 I32 numbered_buff_LENGTH (pTHX_
422 Get the C<length> of a capture variable. There's a special callback
423 for this so that Perl doesn't have to do a FETCH and run C<length> on
424 the result, since the length is (in Perl's case) known from an offset
425 stored in C<< rx->offs >>, this is much more efficient:
427 I32 s1 = rx->offs[paren].start;
428 I32 s2 = rx->offs[paren].end;
431 This is a little bit more complex in the case of UTF-8, see what
432 C<Perl_reg_numbered_buff_length> does with
433 L<is_utf8_string_loclen|perlapi/is_utf8_string_loclen>.
435 =head2 Named capture callbacks
437 Called to get/set the value of C<%+> and C<%->, as well as by some
438 utility functions in L<re>.
440 There are two callbacks, C<named_buff> is called in all the cases the
441 FETCH, STORE, DELETE, CLEAR, EXISTS and SCALAR L<Tie::Hash> callbacks
442 would be on changes to C<%+> and C<%-> and C<named_buff_iter> in the
443 same cases as FIRSTKEY and NEXTKEY.
445 The C<flags> parameter can be used to determine which of these
446 operations the callbacks should respond to. The following flags are
449 Which L<Tie::Hash> operation is being performed from the Perl level on
450 C<%+> or C<%+>, if any:
461 If C<%+> or C<%-> is being operated on, if any.
466 If this is being called as C<re::regname>, C<re::regnames> or
467 C<re::regnames_count>, if any. The first two will be combined with
468 C<RXapif_ONE> or C<RXapif_ALL>.
472 RXapif_REGNAMES_COUNT
474 Internally C<%+> and C<%-> are implemented with a real tied interface
475 via L<Tie::Hash::NamedCapture>. The methods in that package will call
476 back into these functions. However the usage of
477 L<Tie::Hash::NamedCapture> for this purpose might change in future
478 releases. For instance this might be implemented by magic instead
479 (would need an extension to mgvtbl).
483 SV* (*named_buff) (pTHX_ REGEXP * const rx, SV * const key,
484 SV * const value, U32 flags);
486 =head3 named_buff_iter
488 SV* (*named_buff_iter) (pTHX_
490 const SV * const lastkey,
495 SV* qr_package(pTHX_ REGEXP * const rx);
497 The package the qr// magic object is blessed into (as seen by C<ref
498 qr//>). It is recommended that engines change this to their package
499 name for identification regardless of if they implement methods
502 The package this method returns should also have the internal
503 C<Regexp> package in its C<@ISA>. C<< qr//->isa("Regexp") >> should always
504 be true regardless of what engine is being used.
506 Example implementation might be:
509 Example_qr_package(pTHX_ REGEXP * const rx)
512 return newSVpvs("re::engine::Example");
515 Any method calls on an object created with C<qr//> will be dispatched to the
516 package as a normal object.
518 use re::engine::Example;
520 $re->meth; # dispatched to re::engine::Example::meth()
522 To retrieve the C<REGEXP> object from the scalar in an XS function use
523 the C<SvRX> macro, see L<"REGEXP Functions" in perlapi|perlapi/REGEXP
528 REGEXP * re = SvRX(sv);
532 void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
534 On threaded builds a regexp may need to be duplicated so that the pattern
535 can be used by multiple threads. This routine is expected to handle the
536 duplication of any private data pointed to by the C<pprivate> member of
537 the C<regexp> structure. It will be called with the preconstructed new
538 C<regexp> structure as an argument, the C<pprivate> member will point at
539 the B<old> private structure, and it is this routine's responsibility to
540 construct a copy and return a pointer to it (which Perl will then use to
541 overwrite the field as passed to this routine.)
543 This allows the engine to dupe its private data but also if necessary
544 modify the final structure if it really must.
546 On unthreaded builds this field doesn't exist.
550 This is private to the Perl core and subject to change. Should be left
553 =head1 The REGEXP structure
555 The REGEXP struct is defined in F<regexp.h>.
556 All regex engines must be able to
557 correctly build such a structure in their L</comp> routine.
559 The REGEXP structure contains all the data that Perl needs to be aware of
560 to properly work with the regular expression. It includes data about
561 optimisations that Perl can use to determine if the regex engine should
562 really be used, and various other control info that is needed to properly
563 execute patterns in various contexts, such as if the pattern anchored in
564 some way, or what flags were used during the compile, or if the
565 program contains special constructs that Perl needs to be aware of.
567 In addition it contains two fields that are intended for the private
568 use of the regex engine that compiled the pattern. These are the
569 C<intflags> and C<pprivate> members. C<pprivate> is a void pointer to
570 an arbitrary structure, whose use and management is the responsibility
571 of the compiling engine. Perl will never modify either of these
574 typedef struct regexp {
575 /* what engine created this regexp? */
576 const struct regexp_engine* engine;
578 /* what re is this a lightweight copy of? */
579 struct regexp* mother_re;
581 /* Information about the match that the Perl core uses to manage
583 U32 extflags; /* Flags used both externally and internally */
584 I32 minlen; /* mininum possible number of chars in */
586 I32 minlenret; /* mininum possible number of chars in $& */
587 U32 gofs; /* chars left of pos that we search from */
589 /* substring data about strings that must appear
590 in the final match, used for optimisations */
591 struct reg_substr_data *substrs;
593 U32 nparens; /* number of capture groups */
595 /* private engine specific data */
596 U32 intflags; /* Engine Specific Internal flags */
597 void *pprivate; /* Data private to the regex engine which
598 created this object. */
600 /* Data about the last/current match. These are modified during
602 U32 lastparen; /* highest close paren matched ($+) */
603 U32 lastcloseparen; /* last close paren matched ($^N) */
604 regexp_paren_pair *swap; /* Swap copy of *offs */
605 regexp_paren_pair *offs; /* Array of offsets for (@-) and
608 char *subbeg; /* saved or original string so \digit works
610 SV_SAVED_COPY /* If non-NULL, SV which is COW from original */
611 I32 sublen; /* Length of string pointed by subbeg */
612 I32 suboffset; /* byte offset of subbeg from logical start of
614 I32 subcoffset; /* suboffset equiv, but in chars (for @-/@+) */
616 /* Information about the match that isn't often used */
617 I32 prelen; /* length of precomp */
618 const char *precomp; /* pre-compilation regular expression */
620 char *wrapped; /* wrapped version of the pattern */
621 I32 wraplen; /* length of wrapped */
623 I32 seen_evals; /* number of eval groups in the pattern - for
625 HV *paren_names; /* Optional hash of paren names */
627 /* Refcount of this regexp */
628 I32 refcnt; /* Refcount of this regexp */
631 The fields are discussed in more detail below:
635 This field points at a C<regexp_engine> structure which contains pointers
636 to the subroutines that are to be used for performing a match. It
637 is the compiling routine's responsibility to populate this field before
638 returning the regexp object.
640 Internally this is set to C<NULL> unless a custom engine is specified in
641 C<$^H{regcomp}>, Perl's own set of callbacks can be accessed in the struct
642 pointed to by C<RE_ENGINE_PTR>.
646 TODO, see L<http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html>
650 This will be used by Perl to see what flags the regexp was compiled
651 with, this will normally be set to the value of the flags parameter by
652 the L<comp|/comp> callback. See the L<comp|/comp> documentation for
655 =head2 C<minlen> C<minlenret>
657 The minimum string length (in characters) required for the pattern to match.
659 prune the search space by not bothering to match any closer to the end of a
660 string than would allow a match. For instance there is no point in even
661 starting the regex engine if the minlen is 10 but the string is only 5
662 characters long. There is no way that the pattern can match.
664 C<minlenret> is the minimum length (in characters) of the string that would
665 be found in $& after a match.
667 The difference between C<minlen> and C<minlenret> can be seen in the
672 where the C<minlen> would be 3 but C<minlenret> would only be 2 as the \d is
673 required to match but is not actually
674 included in the matched content. This
675 distinction is particularly important as the substitution logic uses the
676 C<minlenret> to tell if it can do in-place substitutions (these can
677 result in considerable speed-up).
681 Left offset from pos() to start match at.
685 Substring data about strings that must appear in the final match. This
686 is currently only used internally by Perl's engine, but might be
687 used in the future for all engines for optimisations.
689 =head2 C<nparens>, C<lastparen>, and C<lastcloseparen>
691 These fields are used to keep track of how many paren groups could be matched
692 in the pattern, which was the last open paren to be entered, and which was
693 the last close paren to be entered.
697 The engine's private copy of the flags the pattern was compiled with. Usually
698 this is the same as C<extflags> unless the engine chose to modify one of them.
702 A void* pointing to an engine-defined
703 data structure. The Perl engine uses the
704 C<regexp_internal> structure (see L<perlreguts/Base Structures>) but a custom
705 engine should use something else.
709 Unused. Left in for compatibility with Perl 5.10.0.
713 A C<regexp_paren_pair> structure which defines offsets into the string being
714 matched which correspond to the C<$&> and C<$1>, C<$2> etc. captures, the
715 C<regexp_paren_pair> struct is defined as follows:
717 typedef struct regexp_paren_pair {
722 If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that
723 capture group did not match.
724 C<< ->offs[0].start/end >> represents C<$&> (or
725 C<${^MATCH}> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where
728 =head2 C<precomp> C<prelen>
730 Used for optimisations. C<precomp> holds a copy of the pattern that
731 was compiled and C<prelen> its length. When a new pattern is to be
732 compiled (such as inside a loop) the internal C<regcomp> operator
733 checks if the last compiled C<REGEXP>'s C<precomp> and C<prelen>
734 are equivalent to the new one, and if so uses the old pattern instead
735 of compiling a new one.
737 The relevant snippet from C<Perl_pp_regcomp>:
739 if (!re || !re->precomp || re->prelen != (I32)len ||
740 memNE(re->precomp, t, len))
741 /* Compile a new pattern */
743 =head2 C<paren_names>
745 This is a hash used internally to track named capture groups and their
746 offsets. The keys are the names of the buffers the values are dualvars,
747 with the IV slot holding the number of buffers with the given name and the
748 pv being an embedded array of I32. The values may also be contained
749 independently in the data array in cases where named backreferences are
754 Holds information on the longest string that must occur at a fixed
755 offset from the start of the pattern, and the longest string that must
756 occur at a floating offset from the start of the pattern. Used to do
757 Fast-Boyer-Moore searches on the string to find out if its worth using
758 the regex engine at all, and if so where in the string to search.
760 =head2 C<subbeg> C<sublen> C<saved_copy> C<suboffset> C<subcoffset>
762 Used during the execution phase for managing search and replace patterns,
763 and for providing the text for C<$&>, C<$1> etc. C<subbeg> points to a
764 buffer (either the original string, or a copy in the case of
765 C<RX_MATCH_COPIED(rx)>), and C<sublen> is the length of the buffer. The
766 C<RX_OFFS> start and end indices index into this buffer.
768 In the presence of the C<REXEC_COPY_STR> flag, but with the addition of
769 the C<REXEC_COPY_SKIP_PRE> or C<REXEC_COPY_SKIP_POST> flags, an engine
770 can choose not to copy the full buffer (although it must still do so in
771 the presence of C<RXf_PMf_KEEPCOPY> or the relevant bits being set in
772 C<PL_sawampersand>). In this case, it may set C<suboffset> to indicate the
773 number of bytes from the logical start of the buffer to the physical start
774 (i.e. C<subbeg>). It should also set C<subcoffset>, the number of
775 characters in the offset. The latter is needed to support C<@-> and C<@+>
776 which work in characters, not bytes.
778 =head2 C<wrapped> C<wraplen>
780 Stores the string C<qr//> stringifies to. The Perl engine for example
781 stores C<(?^:eek)> in the case of C<qr/eek/>.
783 When using a custom engine that doesn't support the C<(?:)> construct
784 for inline modifiers, it's probably best to have C<qr//> stringify to
785 the supplied pattern, note that this will create undesired patterns in
788 my $x = qr/a|b/; # "a|b"
789 my $y = qr/c/i; # "c"
790 my $z = qr/$x$y/; # "a|bc"
792 There's no solution for this problem other than making the custom
793 engine understand a construct like C<(?:)>.
797 This stores the number of eval groups in
798 the pattern. This is used for security
799 purposes when embedding compiled regexes into larger patterns with C<qr//>.
803 The number of times the structure is referenced. When
804 this falls to 0, the regexp is automatically freed
805 by a call to pregfree. This should be set to 1 in
806 each engine's L</comp> routine.
810 Originally part of L<perlreguts>.
814 Originally written by Yves Orton, expanded by E<AElig>var ArnfjE<ouml>rE<eth>
819 Copyright 2006 Yves Orton and 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason.
821 This program is free software; you can redistribute it and/or modify it under
822 the same terms as Perl itself.