/[pcre]/code/trunk/doc/pcrecompat.3
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revision 458 by ph10, Sat Oct 3 16:24:08 2009 UTC revision 459 by ph10, Sun Oct 4 09:21:39 2009 UTC
# Line 98  the pattern /^(a(b)?)+$/ in Perl leaves Line 98  the pattern /^(a(b)?)+$/ in Perl leaves
98  argument. PCRE does not support (*MARK).  argument. PCRE does not support (*MARK).
99  .P  .P
100  12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern  12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern
101  names is not as general as Perl's. This is a consequence of the fact the PCRE  names is not as general as Perl's. This is a consequence of the fact the PCRE
102  works internally just with numbers, using an external table to translate  works internally just with numbers, using an external table to translate
103  between numbers and names. The following are some specific differences:  between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),
104  .sp  where the two capturing parentheses have the same number but different names,
105  (a) A pattern such as (?|(?<a>A)|(?<b)B), where the two capturing  is not supported, and causes an error at compile time. If it were allowed, it
106  parentheses have the same number but different names, is not supported, and  would not be possible to distinguish which parentheses matched, because both
107  causes an error at compile time. If it were allowed, it would not be possible  names map to capturing subpattern number 1. To avoid this confusing situation,
108  to distinguish which parentheses matched, because both names map to capturing  an error is given at compile time.
 subpattern number 1. To avoid this confusing situation, an error is given at  
 compile time.  
 .sp  
 (b) A condition test for a subpattern with a name that is duplicated gives  
 unpredictable results. For example, when the pattern  
 (?:(?<a>A)|(?<a>B))(?('a')...|...) is compiled (the PCRE_DUPNAMES option is  
 required), the condition test (?('a') is set to test whether subpattern 1 has  
 matched, ignoring subpattern 2, even though it has the same name.  
109  .P  .P
110  13. PCRE provides some extensions to the Perl regular expression facilities.  13. PCRE provides some extensions to the Perl regular expression facilities.
111  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 172  Cambridge CB2 3QH, England. Line 164  Cambridge CB2 3QH, England.
164  .rs  .rs
165  .sp  .sp
166  .nf  .nf
167  Last updated: 03 October 2009  Last updated: 04 October 2009
168  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2009 University of Cambridge.
169  .fi  .fi

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