+=head1 PERFORMANCE
+
+NOTE: This was fixed in perl 5.20. Mentioning these three variables no
+longer makes a speed difference. This section still applies if your code
+is to run on perl 5.18 or earlier.
+
+This module can provoke sizeable inefficiencies for regular expressions,
+due to unfortunate implementation details. If performance matters in
+your application and you don't need $PREMATCH, $MATCH, or $POSTMATCH,
+try doing