From: Rafael Garcia-Suarez <rgarciasuarez@gmail.com>
Date: Thu, 26 Oct 2006 16:11:26 +0000 (+0000)
Subject: Document the new (?FAIL) assertion (Yves Orton)
X-Git-Tag: accepted/trunk/20130322.191538~16765
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=286f584ab7c58e3769088aa5b01f152848311dbc;p=platform%2Fupstream%2Fperl.git

Document the new (?FAIL) assertion (Yves Orton)

p4raw-id: //depot/perl@29119
---

diff --git a/pod/perlre.pod b/pod/perlre.pod
index 1a95297..b46b381 100644
--- a/pod/perlre.pod
+++ b/pod/perlre.pod
@@ -933,6 +933,15 @@ the same name, then it recurses to the leftmost.
 It is an error to refer to a name that is not declared somewhere in the
 pattern.
 
+=item C<(?FAIL)> C<(?F)>
+X<(?FAIL)> X<(?F)>
+
+This pattern matches nothing and always fails. It can be used to force the
+engine to backtrack. It is equivalent to C<(?!)>, but easier to read. In
+fact, C<(?!)> gets optimised into C<(?FAIL)> internally.
+
+It is probably useful only when combined with C<(?{})> or C<(??{})>.
+
 =item C<< (?>pattern) >>
 X<backtrack> X<backtracking> X<atomic> X<possessive>