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PERLREAPI(1)	       Perl Programmers	Reference Guide		  PERLREAPI(1)

NAME
       perlreapi - Perl	regular	expression plugin interface

DESCRIPTION
       As of Perl 5.9.5	there is a new interface for plugging and using
       regular expression engines other	than the default one.

       Each engine is supposed to provide access to a constant structure of
       the following format:

	   typedef struct regexp_engine	{
	       REGEXP* (*comp) (pTHX_
				const SV * const pattern, const	U32 flags);
	       I32     (*exec) (pTHX_
				REGEXP * const rx,
				char* stringarg,
				char* strend, char* strbeg,
				SSize_t	minend,	SV* sv,
				void* data, U32	flags);
	       char*   (*intuit) (pTHX_
				  REGEXP * const rx, SV	*sv,
				  const	char * const strbeg,
				  char *strpos,	char *strend, U32 flags,
				  struct re_scream_pos_data_s *data);
	       SV*     (*checkstr) (pTHX_ REGEXP * const rx);
	       void    (*free) (pTHX_ REGEXP * const rx);
	       void    (*numbered_buff_FETCH) (pTHX_
					       REGEXP *	const rx,
					       const I32 paren,
					       SV * const sv);
	       void    (*numbered_buff_STORE) (pTHX_
					       REGEXP *	const rx,
					       const I32 paren,
					       SV const	* const	value);
	       I32     (*numbered_buff_LENGTH) (pTHX_
						REGEXP * const rx,
						const SV * const sv,
						const I32 paren);
	       SV*     (*named_buff) (pTHX_
				      REGEXP * const rx,
				      SV * const key,
				      SV * const value,
				      U32 flags);
	       SV*     (*named_buff_iter) (pTHX_
					   REGEXP * const rx,
					   const SV * const lastkey,
					   const U32 flags);
	       SV*     (*qr_package)(pTHX_ REGEXP * const rx);
	   #ifdef USE_ITHREADS
	       void*   (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param);
	   #endif
	       REGEXP* (*op_comp) (...);

       When a regexp is	compiled, its "engine" field is	then set to point at
       the appropriate structure, so that when it needs	to be used Perl	can
       find the	right routines to do so.

       In order	to install a new regexp	handler, $^H{regcomp} is set to	an
       integer which (when casted appropriately) resolves to one of these
       structures.  When compiling, the	"comp" method is executed, and the
       resulting "regexp" structure's engine field is expected to point	back
       at the same structure.

       The pTHX_ symbol	in the definition is a macro used by Perl under
       threading to provide an extra argument to the routine holding a pointer
       back to the interpreter that is executing the regexp. So	under
       threading all routines get an extra argument.

Callbacks
   comp
	   REGEXP* comp(pTHX_ const SV * const pattern,	const U32 flags);

       Compile the pattern stored in "pattern" using the given "flags" and
       return a	pointer	to a prepared "REGEXP" structure that can perform the
       match.  See "The	REGEXP structure" below	for an explanation of the
       individual fields in the	REGEXP struct.

       The "pattern" parameter is the scalar that was used as the pattern.
       Previous	versions of Perl would pass two	"char*"	indicating the start
       and end of the stringified pattern; the following snippet can be	used
       to get the old parameters:

	   STRLEN plen;
	   char*  exp =	SvPV(pattern, plen);
	   char* xend =	exp + plen;

       Since any scalar	can be passed as a pattern, it's possible to implement
       an engine that does something with an array (""ook" =~ [	qw/ eek	hlagh
       / ]") or	with the non-stringified form of a compiled regular expression
       (""ook" =~ qr/eek/").  Perl's own engine	will always stringify
       everything using	the snippet above, but that doesn't mean other engines
       have to.

       The "flags" parameter is	a bitfield which indicates which of the
       "msixpn"	flags the regex	was compiled with.  It also contains
       additional info,	such as	if "use	locale"	is in effect.

       The "eogc" flags	are stripped out before	being passed to	the comp
       routine.	 The regex engine does not need	to know	if any of these	are
       set, as those flags should only affect what Perl	does with the pattern
       and its match variables,	not how	it gets	compiled and executed.

       By the time the comp callback is	called,	some of	these flags have
       already had effect (noted below where applicable).  However most	of
       their effect occurs after the comp callback has run, in routines	that
       read the	"rx->extflags" field which it populates.

       In general the flags should be preserved	in "rx->extflags" after
       compilation, although the regex engine might want to add	or delete some
       of them to invoke or disable some special behavior in Perl.  The	flags
       along with any special behavior they cause are documented below:

       The pattern modifiers:

       "/m" - RXf_PMf_MULTILINE
	   If this is in "rx->extflags"	it will	be passed to "Perl_fbm_instr"
	   by "pp_split" which will treat the subject string as	a multi-line
	   string.

       "/s" - RXf_PMf_SINGLELINE
       "/i" - RXf_PMf_FOLD
       "/x" - RXf_PMf_EXTENDED
	   If present on a regex, "#" comments will be handled differently by
	   the tokenizer in some cases.

	   TODO: Document those	cases.

       "/p" - RXf_PMf_KEEPCOPY
	   TODO: Document this

       Character set
	   The character set rules are determined by an	enum that is contained
	   in this field.  This	is still experimental and subject to change,
	   but the current interface returns the rules by use of the in-line
	   function "get_regex_charset(const U32 flags)".  The only currently
	   documented value returned from it is	REGEX_LOCALE_CHARSET, which is
	   set if "use locale" is in effect. If	present	in "rx->extflags",
	   "split" will	use the	locale dependent definition of whitespace when
	   RXf_SKIPWHITE or RXf_WHITE is in effect.  ASCII whitespace is
	   defined as per isSPACE, and by the internal macros "is_utf8_space"
	   under UTF-8,	and "isSPACE_LC" under "use locale".

       Additional flags:

       RXf_SPLIT
	   This	flag was removed in perl 5.18.0.  "split ' '" is now special-
	   cased solely	in the parser.	RXf_SPLIT is still #defined, so	you
	   can test for	it.  This is how it used to work:

	   If "split" is invoked as "split ' '"	or with	no arguments (which
	   really means	"split(' ', $_)", see split), Perl will	set this flag.
	   The regex engine can	then check for it and set the SKIPWHITE	and
	   WHITE extflags.  To do this,	the Perl engine	does:

	       if (flags & RXf_SPLIT &&	r->prelen == 1 && r->precomp[0]	== ' ')
		   r->extflags |= (RXf_SKIPWHITE|RXf_WHITE);

       These flags can be set during compilation to enable optimizations in
       the "split" operator.

       RXf_SKIPWHITE
	   This	flag was removed in perl 5.18.0.  It is	still #defined,	so you
	   can set it, but doing so will have no effect.  This is how it used
	   to work:

	   If the flag is present in "rx->extflags" "split" will delete
	   whitespace from the start of	the subject string before it's
	   operated on.	 What is considered whitespace depends on if the
	   subject is a	UTF-8 string and if the	"RXf_PMf_LOCALE" flag is set.

	   If RXf_WHITE	is set in addition to this flag, "split" will behave
	   like	"split " "" under the Perl engine.

       RXf_START_ONLY
	   Tells the split operator to split the target	string on newlines
	   ("\n") without invoking the regex engine.

	   Perl's engine sets this if the pattern is "/^/" ("plen == 1 && *exp
	   == '^'"), even under	"/^/s";	see split.  Of course a	different
	   regex engine	might want to use the same optimizations with a
	   different syntax.

       RXf_WHITE
	   Tells the split operator to split the target	string on whitespace
	   without invoking the	regex engine.  The definition of whitespace
	   varies depending on if the target string is a UTF-8 string and on
	   if RXf_PMf_LOCALE is	set.

	   Perl's engine sets this flag	if the pattern is "\s+".

       RXf_NULL
	   Tells the split operator to split the target	string on characters.
	   The definition of character varies depending	on if the target
	   string is a UTF-8 string.

	   Perl's engine sets this flag	on empty patterns, this	optimization
	   makes "split	//" much faster	than it	would otherwise	be.  It's even
	   faster than "unpack".

       RXf_NO_INPLACE_SUBST
	   Added in perl 5.18.0, this flag indicates that a regular expression
	   might perform an operation that would interfere with	inplace
	   substitution. For instance it might contain lookbehind, or assign
	   to non-magical variables (such as $REGMARK and $REGERROR) during
	   matching.  "s///" will skip certain optimisations when this is set.

   exec
	   I32 exec(pTHX_ REGEXP * const rx,
		    char *stringarg, char* strend, char* strbeg,
		    SSize_t minend, SV*	sv,
		    void* data,	U32 flags);

       Execute a regexp. The arguments are

       rx  The regular expression to execute.

       sv  This	is the SV to be	matched	against.  Note that the	actual char
	   array to be matched against is supplied by the arguments described
	   below; the SV is just used to determine UTF8ness, "pos()" etc.

       strbeg
	   Pointer to the physical start of the	string.

       strend
	   Pointer to the character following the physical end of the string
	   (i.e.  the "\0", if any).

       stringarg
	   Pointer to the position in the string where matching	should start;
	   it might not	be equal to "strbeg" (for example in a later iteration
	   of "/.../g").

       minend
	   Minimum length of string (measured in bytes from "stringarg") that
	   must	match; if the engine reaches the end of	the match but hasn't
	   reached this	position in the	string,	it should fail.

       data
	   Optimisation	data; subject to change.

       flags
	   Optimisation	flags; subject to change.

   intuit
	   char* intuit(pTHX_
		       REGEXP *	const rx,
		       SV *sv,
		       const char * const strbeg,
		       char *strpos,
		       char *strend,
		       const U32 flags,
		       struct re_scream_pos_data_s *data);

       Find the	start position where a regex match should be attempted,	or
       possibly	if the regex engine should not be run because the pattern
       can't match.  This is called, as	appropriate, by	the core, depending on
       the values of the "extflags" member of the "regexp" structure.

       Arguments:

	   rx:	   the regex to	match against
	   sv:	   the SV being	matched: only used for utf8 flag; the string
		   itself is accessed via the pointers below. Note that	on
		   something like an overloaded	SV, SvPOK(sv) may be false
		   and the string pointers may point to	something unrelated to
		   the SV itself.
	   strbeg: real	beginning of string
	   strpos: the point in	the string at which to begin matching
	   strend: pointer to the byte following the last char of the string
	   flags   currently unused; set to 0
	   data:   currently unused; set to NULL

   checkstr
	   SV* checkstr(pTHX_ REGEXP * const rx);

       Return a	SV containing a	string that must appear	in the pattern.	Used
       by "split" for optimising matches.

   free
	   void	free(pTHX_ REGEXP * const rx);

       Called by Perl when it is freeing a regexp pattern so that the engine
       can release any resources pointed to by the "pprivate" member of	the
       "regexp"	structure.  This is only responsible for freeing private data;
       Perl will handle	releasing anything else	contained in the "regexp"
       structure.

   Numbered capture callbacks
       Called to get/set the value of "$`", "$'", $& and their named
       equivalents, ${^PREMATCH}, ${^POSTMATCH}	and ${^MATCH}, as well as the
       numbered	capture	groups ($1, $2,	...).

       The "paren" parameter will be 1 for $1, 2 for $2	and so forth, and have
       these symbolic values for the special variables:

	   ${^PREMATCH}	 RX_BUFF_IDX_CARET_PREMATCH
	   ${^POSTMATCH} RX_BUFF_IDX_CARET_POSTMATCH
	   ${^MATCH}	 RX_BUFF_IDX_CARET_FULLMATCH
	   $`		 RX_BUFF_IDX_PREMATCH
	   $'		 RX_BUFF_IDX_POSTMATCH
	   $&		 RX_BUFF_IDX_FULLMATCH

       Note that in Perl 5.17.3	and earlier, the last three constants were
       also used for the caret variants	of the variables.

       The names have been chosen by analogy with Tie::Scalar methods names
       with an additional LENGTH callback for efficiency.  However named
       capture variables are currently not tied	internally but implemented via
       magic.

       numbered_buff_FETCH

	   void	numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren,
				    SV * const sv);

       Fetch a specified numbered capture.  "sv" should	be set to the scalar
       to return, the scalar is	passed as an argument rather than being
       returned	from the function because when it's called Perl	already	has a
       scalar to store the value, creating another one would be	redundant.
       The scalar can be set with "sv_setsv", "sv_setpvn" and friends, see
       perlapi.

       This callback is	where Perl untaints its	own capture variables under
       taint mode (see perlsec).  See the "Perl_reg_numbered_buff_fetch"
       function	in regcomp.c for how to	untaint	capture	variables if that's
       something you'd like your engine	to do as well.

       numbered_buff_STORE

	   void	   (*numbered_buff_STORE) (pTHX_
					   REGEXP * const rx,
					   const I32 paren,
					   SV const * const value);

       Set the value of	a numbered capture variable.  "value" is the scalar
       that is to be used as the new value.  It's up to	the engine to make
       sure this is used as the	new value (or reject it).

       Example:

	   if ("ook" =~	/(o*)/)	{
	       # 'paren' will be '1' and 'value' will be 'ee'
	       $1 =~ tr/o/e/;
	   }

       Perl's own engine will croak on any attempt to modify the capture
       variables, to do	this in	another	engine use the following callback
       (copied from "Perl_reg_numbered_buff_store"):

	   void
	   Example_reg_numbered_buff_store(pTHX_
					   REGEXP * const rx,
					   const I32 paren,
					   SV const * const value)
	   {
	       PERL_UNUSED_ARG(rx);
	       PERL_UNUSED_ARG(paren);
	       PERL_UNUSED_ARG(value);

	       if (!PL_localizing)
		   Perl_croak(aTHX_ PL_no_modify);
	   }

       Actually	Perl will not always croak in a	statement that looks like it
       would modify a numbered capture variable.  This is because the STORE
       callback	will not be called if Perl can determine that it doesn't have
       to modify the value.  This is exactly how tied variables	behave in the
       same situation:

	   package CaptureVar;
	   use parent 'Tie::Scalar';

	   sub TIESCALAR { bless [] }
	   sub FETCH { undef }
	   sub STORE { die "This doesn't get called" }

	   package main;

	   tie my $sv => "CaptureVar";
	   $sv =~ y/a/b/;

       Because $sv is "undef" when the "y///" operator is applied to it, the
       transliteration won't actually execute and the program won't "die".
       This is different to how	5.8 and	earlier	versions behaved since the
       capture variables were READONLY variables then; now they'll just	die
       when assigned to	in the default engine.

       numbered_buff_LENGTH

	   I32 numbered_buff_LENGTH (pTHX_
				     REGEXP * const rx,
				     const SV *	const sv,
				     const I32 paren);

       Get the "length"	of a capture variable.	There's	a special callback for
       this so that Perl doesn't have to do a FETCH and	run "length" on	the
       result, since the length	is (in Perl's case) known from an offset
       stored in "rx->offs", this is much more efficient:

	   I32 s1  = rx->offs[paren].start;
	   I32 s2  = rx->offs[paren].end;
	   I32 len = t1	- s1;

       This is a little	bit more complex in the	case of	UTF-8, see what
       "Perl_reg_numbered_buff_length" does with is_utf8_string_loclen.

   Named capture callbacks
       Called to get/set the value of "%+" and "%-", as	well as	by some
       utility functions in re.

       There are two callbacks,	"named_buff" is	called in all the cases	the
       FETCH, STORE, DELETE, CLEAR, EXISTS and SCALAR Tie::Hash	callbacks
       would be	on changes to "%+" and "%-" and	"named_buff_iter" in the same
       cases as	FIRSTKEY and NEXTKEY.

       The "flags" parameter can be used to determine which of these
       operations the callbacks	should respond to.  The	following flags	are
       currently defined:

       Which Tie::Hash operation is being performed from the Perl level	on
       "%+" or "%+", if	any:

	   RXapif_FETCH
	   RXapif_STORE
	   RXapif_DELETE
	   RXapif_CLEAR
	   RXapif_EXISTS
	   RXapif_SCALAR
	   RXapif_FIRSTKEY
	   RXapif_NEXTKEY

       If "%+" or "%-" is being	operated on, if	any.

	   RXapif_ONE /* %+ */
	   RXapif_ALL /* %- */

       If this is being	called as "re::regname", "re::regnames"	or
       "re::regnames_count", if	any.  The first	two will be combined with
       "RXapif_ONE" or "RXapif_ALL".

	   RXapif_REGNAME
	   RXapif_REGNAMES
	   RXapif_REGNAMES_COUNT

       Internally "%+" and "%-"	are implemented	with a real tied interface via
       Tie::Hash::NamedCapture.	 The methods in	that package will call back
       into these functions.  However the usage	of Tie::Hash::NamedCapture for
       this purpose might change in future releases.  For instance this	might
       be implemented by magic instead (would need an extension	to mgvtbl).

       named_buff

	   SV*	   (*named_buff) (pTHX_	REGEXP * const rx, SV *	const key,
				  SV * const value, U32	flags);

       named_buff_iter

	   SV*	   (*named_buff_iter) (pTHX_
				       REGEXP *	const rx,
				       const SV	* const	lastkey,
				       const U32 flags);

   qr_package
	   SV* qr_package(pTHX_	REGEXP * const rx);

       The package the qr// magic object is blessed into (as seen by "ref
       qr//").	It is recommended that engines change this to their package
       name for	identification regardless of if	they implement methods on the
       object.

       The package this	method returns should also have	the internal "Regexp"
       package in its @ISA.  "qr//->isa("Regexp")" should always be true
       regardless of what engine is being used.

       Example implementation might be:

	   SV*
	   Example_qr_package(pTHX_ REGEXP * const rx)
	   {
	       PERL_UNUSED_ARG(rx);
	       return newSVpvs("re::engine::Example");
	   }

       Any method calls	on an object created with "qr//" will be dispatched to
       the package as a	normal object.

	   use re::engine::Example;
	   my $re = qr//;
	   $re->meth; #	dispatched to re::engine::Example::meth()

       To retrieve the "REGEXP"	object from the	scalar in an XS	function use
       the "SvRX" macro, see "REGEXP Functions"	in perlapi.

	   void	meth(SV	* rv)
	   PPCODE:
	       REGEXP *	re = SvRX(sv);

   dupe
	   void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param);

       On threaded builds a regexp may need to be duplicated so	that the
       pattern can be used by multiple threads.	 This routine is expected to
       handle the duplication of any private data pointed to by	the "pprivate"
       member of the "regexp" structure.  It will be called with the
       preconstructed new "regexp" structure as	an argument, the "pprivate"
       member will point at the	old private structure, and it is this
       routine's responsibility	to construct a copy and	return a pointer to it
       (which Perl will	then use to overwrite the field	as passed to this
       routine.)

       This allows the engine to dupe its private data but also	if necessary
       modify the final	structure if it	really must.

       On unthreaded builds this field doesn't exist.

   op_comp
       This is private to the Perl core	and subject to change. Should be left
       null.

The REGEXP structure
       The REGEXP struct is defined in regexp.h.  All regex engines must be
       able to correctly build such a structure	in their "comp"	routine.

       The REGEXP structure contains all the data that Perl needs to be	aware
       of to properly work with	the regular expression.	 It includes data
       about optimisations that	Perl can use to	determine if the regex engine
       should really be	used, and various other	control	info that is needed to
       properly	execute	patterns in various contexts, such as if the pattern
       anchored	in some	way, or	what flags were	used during the	compile, or if
       the program contains special constructs that Perl needs to be aware of.

       In addition it contains two fields that are intended for	the private
       use of the regex	engine that compiled the pattern.  These are the
       "intflags" and "pprivate" members.  "pprivate" is a void	pointer	to an
       arbitrary structure, whose use and management is	the responsibility of
       the compiling engine.  Perl will	never modify either of these values.

	   typedef struct regexp {
	       /* what engine created this regexp? */
	       const struct regexp_engine* engine;

	       /* what re is this a lightweight	copy of? */
	       struct regexp* mother_re;

	       /* Information about the	match that the Perl core uses to manage
		* things */
	       U32 extflags;   /* Flags	used both externally and internally */
	       I32 minlen;     /* mininum possible number of chars in */
				  string to match */
	       I32 minlenret;  /* mininum possible number of chars in $& */
	       U32 gofs;       /* chars	left of	pos that we search from	*/

	       /* substring data about strings that must appear
		  in the final match, used for optimisations */
	       struct reg_substr_data *substrs;

	       U32 nparens;  /*	number of capture groups */

	       /* private engine specific data */
	       U32 intflags;   /* Engine Specific Internal flags */
	       void *pprivate; /* Data private to the regex engine which
				  created this object. */

	       /* Data about the last/current match. These are modified	during
		* matching*/
	       U32 lastparen;		 /* highest close paren	matched	($+) */
	       U32 lastcloseparen;	 /* last close paren matched ($^N) */
	       regexp_paren_pair *offs;	 /* Array of offsets for (@-) and
					    (@+) */

	       char *subbeg;  /* saved or original string so \digit works
				 forever. */
	       SV_SAVED_COPY  /* If non-NULL, SV which is COW from original */
	       I32 sublen;    /* Length	of string pointed by subbeg */
	       I32 suboffset;  /* byte offset of subbeg	from logical start of
				  str */
	       I32 subcoffset; /* suboffset equiv, but in chars	(for @-/@+) */

	       /* Information about the	match that isn't often used */
	       I32 prelen;	     /*	length of precomp */
	       const char *precomp;  /*	pre-compilation	regular	expression */

	       char *wrapped;  /* wrapped version of the pattern */
	       I32 wraplen;    /* length of wrapped */

	       I32 seen_evals;	 /* number of eval groups in the pattern - for
				    security checks */
	       HV *paren_names;	 /* Optional hash of paren names */

	       /* Refcount of this regexp */
	       I32 refcnt;	       /* Refcount of this regexp */
	   } regexp;

       The fields are discussed	in more	detail below:

   "engine"
       This field points at a "regexp_engine" structure	which contains
       pointers	to the subroutines that	are to be used for performing a	match.
       It is the compiling routine's responsibility to populate	this field
       before returning	the regexp object.

       Internally this is set to "NULL"	unless a custom	engine is specified in
       $^H{regcomp}, Perl's own	set of callbacks can be	accessed in the	struct
       pointed to by "RE_ENGINE_PTR".

   "mother_re"
       TODO, see commit	28d8d7f41a.

   "extflags"
       This will be used by Perl to see	what flags the regexp was compiled
       with, this will normally	be set to the value of the flags parameter by
       the comp	callback.  See the comp	documentation for valid	flags.

   "minlen" "minlenret"
       The minimum string length (in characters) required for the pattern to
       match.  This is used to prune the search	space by not bothering to
       match any closer	to the end of a	string than would allow	a match.  For
       instance	there is no point in even starting the regex engine if the
       minlen is 10 but	the string is only 5 characters	long.  There is	no way
       that the	pattern	can match.

       "minlenret" is the minimum length (in characters) of the	string that
       would be	found in $& after a match.

       The difference between "minlen" and "minlenret" can be seen in the
       following pattern:

	   /ns(?=\d)/

       where the "minlen" would	be 3 but "minlenret" would only	be 2 as	the \d
       is required to match but	is not actually	included in the	matched
       content.	 This distinction is particularly important as the
       substitution logic uses the "minlenret" to tell if it can do in-place
       substitutions (these can	result in considerable speed-up).

   "gofs"
       Left offset from	pos() to start match at.

   "substrs"
       Substring data about strings that must appear in	the final match.  This
       is currently only used internally by Perl's engine, but might be	used
       in the future for all engines for optimisations.

   "nparens", "lastparen", and "lastcloseparen"
       These fields are	used to	keep track of: how many	paren capture groups
       there are in the	pattern; which was the highest paren to	be closed (see
       "$+" in perlvar); and which was the most	recent paren to	be closed (see
       "$^N" in	perlvar).

   "intflags"
       The engine's private copy of the	flags the pattern was compiled with.
       Usually this is the same	as "extflags" unless the engine	chose to
       modify one of them.

   "pprivate"
       A void* pointing	to an engine-defined data structure.  The Perl engine
       uses the	"regexp_internal" structure (see "Base Structures" in
       perlreguts) but a custom	engine should use something else.

   "offs"
       A "regexp_paren_pair" structure which defines offsets into the string
       being matched which correspond to the $&	and $1,	$2 etc.	captures, the
       "regexp_paren_pair" struct is defined as	follows:

	   typedef struct regexp_paren_pair {
	       I32 start;
	       I32 end;
	   } regexp_paren_pair;

       If "->offs[num].start" or "->offs[num].end" is "-1" then	that capture
       group did not match.  "->offs[0].start/end" represents $& (or
       "${^MATCH}" under "/p") and "->offs[paren].end" matches $$paren where
       $paren =	1>.

   "precomp" "prelen"
       Used for	optimisations.	"precomp" holds	a copy of the pattern that was
       compiled	and "prelen" its length.  When a new pattern is	to be compiled
       (such as	inside a loop) the internal "regcomp" operator checks if the
       last compiled "REGEXP"'s	"precomp" and "prelen" are equivalent to the
       new one,	and if so uses the old pattern instead of compiling a new one.

       The relevant snippet from "Perl_pp_regcomp":

	       if (!re || !re->precomp || re->prelen !=	(I32)len ||
		   memNE(re->precomp, t, len))
	       /* Compile a new	pattern	*/

   "paren_names"
       This is a hash used internally to track named capture groups and	their
       offsets.	 The keys are the names	of the buffers the values are
       dualvars, with the IV slot holding the number of	buffers	with the given
       name and	the pv being an	embedded array of I32.	The values may also be
       contained independently in the data array in cases where	named
       backreferences are used.

   "substrs"
       Holds information on the	longest	string that must occur at a fixed
       offset from the start of	the pattern, and the longest string that must
       occur at	a floating offset from the start of the	pattern.  Used to do
       Fast-Boyer-Moore	searches on the	string to find out if its worth	using
       the regex engine	at all,	and if so where	in the string to search.

   "subbeg" "sublen" "saved_copy" "suboffset" "subcoffset"
       Used during the execution phase for managing search and replace
       patterns, and for providing the text for	$&, $1 etc. "subbeg" points to
       a buffer	(either	the original string, or	a copy in the case of
       "RX_MATCH_COPIED(rx)"), and "sublen" is the length of the buffer.  The
       "RX_OFFS" start and end indices index into this buffer.

       In the presence of the "REXEC_COPY_STR" flag, but with the addition of
       the "REXEC_COPY_SKIP_PRE" or "REXEC_COPY_SKIP_POST" flags, an engine
       can choose not to copy the full buffer (although	it must	still do so in
       the presence of "RXf_PMf_KEEPCOPY" or the relevant bits being set in
       "PL_sawampersand").  In this case, it may set "suboffset" to indicate
       the number of bytes from	the logical start of the buffer	to the
       physical	start (i.e. "subbeg").	It should also set "subcoffset", the
       number of characters in the offset. The latter is needed	to support
       "@-" and	"@+" which work	in characters, not bytes.

   "wrapped" "wraplen"
       Stores the string "qr//"	stringifies to.	The Perl engine	for example
       stores "(?^:eek)" in the	case of	"qr/eek/".

       When using a custom engine that doesn't support the "(?:)" construct
       for inline modifiers, it's probably best	to have	"qr//" stringify to
       the supplied pattern, note that this will create	undesired patterns in
       cases such as:

	   my $x = qr/a|b/;  # "a|b"
	   my $y = qr/c/i;   # "c"
	   my $z = qr/$x$y/; # "a|bc"

       There's no solution for this problem other than making the custom
       engine understand a construct like "(?:)".

   "seen_evals"
       This stores the number of eval groups in	the pattern.  This is used for
       security	purposes when embedding	compiled regexes into larger patterns
       with "qr//".

   "refcnt"
       The number of times the structure is referenced.	 When this falls to 0,
       the regexp is automatically freed by a call to "pregfree".  This	should
       be set to 1 in each engine's "comp" routine.

HISTORY
       Originally part of perlreguts.

AUTHORS
       Originally written by Yves Orton, expanded by AEvar Arnfjoer`
       Bjarmason.

LICENSE
       Copyright 2006 Yves Orton and 2007 AEvar	Arnfjoer` Bjarmason.

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

perl v5.35.11			  2022-03-27			  PERLREAPI(1)

NAME | DESCRIPTION | Callbacks | The REGEXP structure | HISTORY | AUTHORS | LICENSE

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