perlreapi.pod: Document RXf_MODIFIES_VARS

diff --git a/pod/perlreapi.pod b/pod/perlreapi.pod
index 68c23ad..ebe81b1 100644 (file)
--- a/pod/perlreapi.pod
+++ b/pod/perlreapi.pod
@@ -223,6 +223,12 @@ Perl's engine sets this flag on empty patterns, this optimization
 makes C<split //> much faster than it would otherwise be. It's even
 faster than C<unpack>.
 
+=item RXf_MODIFIES_VARS
+
+Added in perl 5.18.0, this flag indicates that a regular expression might
+assign to non-magical variables (such as $REGMARK and $REGERROR) during
+matching.  C<s///> will skip certain optimisations when this is set.
+
 =back
 
 =head2 exec