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revision 633 by ph10, Sat Jul 23 14:34:27 2011 UTC revision 678 by ph10, Sun Aug 28 15:23:03 2011 UTC
# Line 10  versions 5.10 and above. Line 10  versions 5.10 and above.
10  .P  .P
11  1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what  1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details of what
12  it does have are given in the  it does have are given in the
 .\" HTML <a href="pcre.html#utf8support">  
 .\" </a>  
 section on UTF-8 support  
 .\"  
 in the main  
13  .\" HREF  .\" HREF
14  \fBpcre\fP  \fBpcreunicode\fP
15  .\"  .\"
16  page.  page.
17  .P  .P
18  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
19  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
20  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
21  character is not "a" three times.  not "a" three times (in principle: PCRE optimizes this to run the assertion
22    just once). Perl allows repeat quantifiers on other assertions such as \eb, but
23    these do not seem to have any use.
24  .P  .P
25  3. Capturing subpatterns that occur inside negative lookahead assertions are  3. Capturing subpatterns that occur inside negative lookahead assertions are
26  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 34  terminated by zero. The escape sequence
34  represent a binary zero.  represent a binary zero.
35  .P  .P
36  5. The following Perl escape sequences are not supported: \el, \eu, \eL,  5. The following Perl escape sequences are not supported: \el, \eu, \eL,
37  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
38  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
39  PCRE, an error is generated.  implemented by Perl's general string-handling and are not part of its pattern
40    matching engine. If any of these are encountered by PCRE, an error is
41    generated.
42  .P  .P
43  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
44  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 50  the internal representation of Unicode c
50  implement the somewhat messy concept of surrogates."  implement the somewhat messy concept of surrogates."
51  .P  .P
52  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
53  \eX match what Unicode calls an "extended grapheme cluster". This is more  \eX match what Unicode calls an "extended grapheme cluster". This is more
54  complicated than an extended Unicode sequence, which is what PCRE matches.  complicated than an extended Unicode sequence, which is what PCRE matches.
55  .P  .P
56  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 106  would not be possible to distinguish whi
106  names map to capturing subpattern number 1. To avoid this confusing situation,  names map to capturing subpattern number 1. To avoid this confusing situation,
107  an error is given at compile time.  an error is given at compile time.
108  .P  .P
109  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,
110  between the ( and ? at the start of a subpattern.  between the ( and ? at the start of a subpattern. If the /x modifier is set,
111    Perl allows whitespace between ( and ? but PCRE never does, even if the
112    PCRE_EXTENDED option is set.
113  .P  .P
114  14. PCRE provides some extensions to the Perl regular expression facilities.  14. PCRE provides some extensions to the Perl regular expression facilities.
115  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 168  Cambridge CB2 3QH, England.
168  .rs  .rs
169  .sp  .sp
170  .nf  .nf
171  Last updated: 23 July 2011  Last updated: 24 August 2011
172  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
173  .fi  .fi

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