/[pcre]/code/trunk/doc/pcrepattern.3
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revision 630 by ph10, Fri Jul 22 10:00:10 2011 UTC revision 637 by ph10, Sun Jul 24 17:44:12 2011 UTC
# Line 1438  items: Line 1438  items:
1438    an escape such as \ed or \epL that matches a single character    an escape such as \ed or \epL that matches a single character
1439    a character class    a character class
1440    a back reference (see next section)    a back reference (see next section)
1441    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (including assertions)
1442    a recursive or "subroutine" call to a subpattern    a recursive or "subroutine" call to a subpattern
1443  .sp  .sp
1444  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
# Line 1829  those that look ahead of the current pos Line 1829  those that look ahead of the current pos
1829  that look behind it. An assertion subpattern is matched in the normal way,  that look behind it. An assertion subpattern is matched in the normal way,
1830  except that it does not cause the current matching position to be changed.  except that it does not cause the current matching position to be changed.
1831  .P  .P
1832  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns. If such an assertion
1833  because it makes no sense to assert the same thing several times. If any kind  contains capturing subpatterns within it, these are counted for the purposes of
1834  of assertion contains capturing subpatterns within it, these are counted for  numbering the capturing subpatterns in the whole pattern. However, substring
1835  the purposes of numbering the capturing subpatterns in the whole pattern.  capturing is carried out only for positive assertions, because it does not make
1836  However, substring capturing is carried out only for positive assertions,  sense for negative assertions.
1837  because it does not make sense for negative assertions.  .P
1838    For compatibility with Perl, assertion subpatterns may be repeated, even though
1839    it makes no sense to assert the same thing several times. In practice, there
1840    only three cases:
1841    .sp
1842    (1) If the quantifier is {0}, the assertion is never obeyed during matching.
1843    However, it may contain internal capturing parenthesized groups that are called
1844    from elsewhere via the
1845    .\" HTML <a href="#subpatternsassubroutines">
1846    .\" </a>
1847    subroutine mechanism.
1848    .\"
1849    .sp
1850    (2) If quantifier is {0,n} where n is greater than zero, it is treated as if it
1851    were {0,1}. At run time, the rest of the pattern match is tried with and
1852    without the assertion, the order depending on the greediness of the quantifier.
1853    .sp
1854    (3) If the minimum repetition is greater than zero, the quantifier is ignored.
1855    The assertion is obeyed just once when encountered during matching.
1856  .  .
1857  .  .
1858  .SS "Lookahead assertions"  .SS "Lookahead assertions"
# Line 2761  Cambridge CB2 3QH, England. Line 2779  Cambridge CB2 3QH, England.
2779  .rs  .rs
2780  .sp  .sp
2781  .nf  .nf
2782  Last updated: 22 July 2011  Last updated: 24 July 2011
2783  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
2784  .fi  .fi

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