/[pcre]/code/trunk/doc/pcrecompat.3
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revision 633 by ph10, Sat Jul 23 14:34:27 2011 UTC revision 654 by ph10, Tue Aug 2 11:00:40 2011 UTC
# Line 20  in the main Line 20  in the main
20  .\"  .\"
21  page.  page.
22  .P  .P
23  2. PCRE does not allow repeat quantifiers on assertions. Perl permits them, but  2. PCRE allows repeat quantifiers only on parenthesized assertions, but they do
24  they do not mean what you might think. For example, (?!a){3} does not assert  not mean what you might think. For example, (?!a){3} does not assert that the
25  that the next three characters are not "a". It just asserts that the next  next three characters are not "a". It just asserts that the next character is
26  character is not "a" three times.  not "a" three times (in principle: PCRE optimizes this to run the assertion
27    just once). Perl allows repeat quantifiers on other assertions such as \eb, but
28    these do not seem to have any use.
29  .P  .P
30  3. Capturing subpatterns that occur inside negative lookahead assertions are  3. Capturing subpatterns that occur inside negative lookahead assertions are
31  counted, but their entries in the offsets vector are never set. Perl sets its  counted, but their entries in the offsets vector are never set. Perl sets its
# Line 37  terminated by zero. The escape sequence Line 39  terminated by zero. The escape sequence
39  represent a binary zero.  represent a binary zero.
40  .P  .P
41  5. The following Perl escape sequences are not supported: \el, \eu, \eL,  5. The following Perl escape sequences are not supported: \el, \eu, \eL,
42  and \eU. In fact these are implemented by Perl's general string-handling and  \eU, and \eN when followed by a character name or Unicode value. (\eN on its
43  are not part of its pattern matching engine. If any of these are encountered by  own, matching a non-newline character, is supported.) In fact these are
44  PCRE, an error is generated.  implemented by Perl's general string-handling and are not part of its pattern
45    matching engine. If any of these are encountered by PCRE, an error is
46    generated.
47  .P  .P
48  6. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE is  6. The Perl escape sequences \ep, \eP, and \eX are supported only if PCRE is
49  built with Unicode character property support. The properties that can be  built with Unicode character property support. The properties that can be
# Line 51  the internal representation of Unicode c Line 55  the internal representation of Unicode c
55  implement the somewhat messy concept of surrogates."  implement the somewhat messy concept of surrogates."
56  .P  .P
57  7. PCRE implements a simpler version of \eX than Perl, which changed to make  7. PCRE implements a simpler version of \eX than Perl, which changed to make
58  \eX match what Unicode calls an "extended grapheme cluster". This is more  \eX match what Unicode calls an "extended grapheme cluster". This is more
59  complicated than an extended Unicode sequence, which is what PCRE matches.  complicated than an extended Unicode sequence, which is what PCRE matches.
60  .P  .P
61  8. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in  8. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in
# Line 107  would not be possible to distinguish whi Line 111  would not be possible to distinguish whi
111  names map to capturing subpattern number 1. To avoid this confusing situation,  names map to capturing subpattern number 1. To avoid this confusing situation,
112  an error is given at compile time.  an error is given at compile time.
113  .P  .P
114  13. Perl recognizes comments in some places that PCRE doesn't, for example,  13. Perl recognizes comments in some places that PCRE does not, for example,
115  between the ( and ? at the start of a subpattern.  between the ( and ? at the start of a subpattern. If the /x modifier is set,
116    Perl allows whitespace between ( and ? but PCRE never does, even if the
117    PCRE_EXTENDED option is set.
118  .P  .P
119  14. PCRE provides some extensions to the Perl regular expression facilities.  14. PCRE provides some extensions to the Perl regular expression facilities.
120  Perl 5.10 includes new features that are not in earlier versions of Perl, some  Perl 5.10 includes new features that are not in earlier versions of Perl, some
# Line 167  Cambridge CB2 3QH, England. Line 173  Cambridge CB2 3QH, England.
173  .rs  .rs
174  .sp  .sp
175  .nf  .nf
176  Last updated: 23 July 2011  Last updated: 24 July 2011
177  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
178  .fi  .fi
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