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Document current assert capture limitation.

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Philip.Hazel 2016-10-23 15:43:42 +00:00
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doc/pcre2pattern.3
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@ -1,4 +1,4 @@
.TH PCRE2PATTERN 3 "14 October 2016" "PCRE2 10.23"
.TH PCRE2PATTERN 3 "23 October 2016" "PCRE2 10.23"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "PCRE2 REGULAR EXPRESSION DETAILS"
@ -2222,6 +2222,13 @@ numbering the capturing subpatterns in the whole pattern. However, substring
capturing is carried out only for positive assertions. (Perl sometimes, but not
always, does do capturing in negative assertions.)
.P
WARNING: If a positive assertion containing one or more capturing subpatterns
succeeds, but failure to match later in the pattern causes backtracking over
this assertion, the captures within the assertion are reset only if no higher
numbered captures are already set. This is, unfortunately, a fundamental
limitation of the current implementation; it may get removed in a future
reworking.
.P
For compatibility with Perl, most assertion subpatterns may be repeated; though
it makes no sense to assert the same thing several times, the side effect of
capturing parentheses may occasionally be useful. However, an assertion that
@ -3470,6 +3477,6 @@ Cambridge, England.
.rs
.sp
.nf
Last updated: 14 October 2016
Last updated: 23 October 2016
Copyright (c) 1997-2016 University of Cambridge.
.fi