/[pcre]/code/trunk/doc/pcrecompat.3
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revision 456 by ph10, Fri Oct 2 08:53:31 2009 UTC revision 461 by ph10, Mon Oct 5 10:59:35 2009 UTC
# Line 77  the Line 77  the
77  documentation for details.  documentation for details.
78  .P  .P
79  9. Subpatterns that are called recursively or as "subroutines" are always  9. Subpatterns that are called recursively or as "subroutines" are always
80  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There
81  is a discussion of an example that explains this in more detail in the  is a discussion of an example that explains this in more detail in the
82  .\" HTML <a href="pcrepattern.html#recursiondifference">  .\" HTML <a href="pcrepattern.html#recursiondifference">
83  .\" </a>  .\" </a>
# Line 97  the pattern /^(a(b)?)+$/ in Perl leaves Line 97  the pattern /^(a(b)?)+$/ in Perl leaves
97  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in the forms without an
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) After matching 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, it is not possible to  would not be possible to distinguish which parentheses matched, because both
107  distinguish which parentheses matched, because both names map to capturing  names map to capturing subpattern number 1. To avoid this confusing situation,
108  subpattern number 1.  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 170  Cambridge CB2 3QH, England. Line 164  Cambridge CB2 3QH, England.
164  .rs  .rs
165  .sp  .sp
166  .nf  .nf
167  Last updated: 29 September 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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