=over 4
-=item RXf_UTF8
-
-Set if the pattern is L<SvUTF8()|perlapi/SvUTF8>, set by Perl_pmruntime.
-
-A regex engine may want to set or disable this flag during
-compilation. The perl engine for instance may upgrade non-UTF-8
-strings to UTF-8 if the pattern includes constructs such as C<\x{...}>
-that can only match Unicode values.
-
=item RXf_SPLIT
If C<split> is invoked as C<split ' '> or with no arguments (which
I32 minend, SV* screamer,
void* data, U32 flags);
-Execute a regexp.
+Execute a regexp. The arguments are
+
+=over 4
+
+=item rx
+
+The regular expression to execute.
+
+=item screamer
+
+This strangely-named arg 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, C<pos()> etc.
+
+=item strbeg
+
+Pointer to the physical start of the string.
+
+=item strend
+
+Pointer to the character following the physical end of the string (i.e.
+the \0).
+
+=item stringarg
+
+Pointer to the position in the string where matching should start; it might
+not be equal to C<strbeg> (for example in a later iteration of C</.../g>).
+
+=item minend
+
+Minimum length of string (measured in bytes from C<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.
+
+=item data
+
+Optimisation data; subject to change.
+
+=item flags
+
+Optimisation flags; subject to change.
+
+=back
=head2 intuit
equivalents, ${^PREMATCH}, ${^POSTMATCH} and $^{MATCH}, as well as the
numbered capture groups (C<$1>, C<$2>, ...).
-The C<paren> parameter will be C<-2> for C<$`>, C<-1> for C<$'>, C<0>
-for C<$&>, C<1> for C<$1> and so forth.
+The C<paren> parameter will be C<1> for C<$1>, C<2> for C<$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
+ $& RX_BUFF_IDX_FULLMATCH
+
+Note that in perl 5.17.3 and earlier, the last three constants were also
+used for the caret variants of the variables.
+
The names have been chosen by analogy with L<Tie::Scalar> methods
names with an additional B<LENGTH> callback for efficiency. However
char *subbeg; /* saved or original string so \digit works forever. */
SV_SAVED_COPY /* If non-NULL, SV which is COW from original */
I32 sublen; /* Length of string pointed by subbeg */
+ I32 suboffset; /* byte offset of subbeg from logical start of str */
+ I32 subcoffset; /* suboffset equiv, but in chars (for @-/@+) */
/* Information about the match that isn't often used */
I32 prelen; /* length of precomp */
If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that
capture group did not match. C<< ->offs[0].start/end >> represents C<$&> (or
-C<${^MATCH> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where
+C<${^MATCH}> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where
C<$paren >= 1>.
=head2 C<precomp> C<prelen>
Fast-Boyer-Moore searches on the string to find out if its worth using
the regex engine at all, and if so where in the string to search.
-=head2 C<subbeg> C<sublen> C<saved_copy>
-
-Used during execution phase for managing search and replace patterns.
+=head2 C<subbeg> C<sublen> C<saved_copy> C<suboffset> C<subcoffset>
+
+Used during the execution phase for managing search and replace patterns,
+and for providing the text for C<$&>, C<$1> etc. C<subbeg> points to a
+buffer (either the original string, or a copy in the case of
+C<RX_MATCH_COPIED(rx)>), and C<sublen> is the length of the buffer. The
+C<RX_OFFS> start and end indices index into this buffer.
+
+In the presence of the C<REXEC_COPY_STR> flag, but with the addition of
+the C<REXEC_COPY_SKIP_PRE> or C<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 C<RXf_PMf_KEEPCOPY> or the relevant bits being set in
+C<PL_sawampersand>). In this case, it may set C<suboffset> to indicate the
+number of bytes from the logical start of the buffer to the physical start
+(i.e. C<subbeg>). It should also set C<subcoffset>, the number of
+characters in the offset. The latter is needed to support C<@-> and C<@+>
+which work in characters, not bytes.
=head2 C<wrapped> C<wraplen>
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