and is useful when the value you are interpolating won't change over
the life of the script. However, mentioning C</o> constitutes a promise
that you won't change the variables in the pattern. If you change them,
-Perl won't even notice. See also L<qr//>.
+Perl won't even notice. See also L<"qr//">.
If the PATTERN evaluates to the empty string, the last
I<successfully> matched regular expression is used instead.
See L<perlfunc/vec> for information on how to manipulate individual bits
in a bit vector.
+=head2 Version tuples
+
+A literal of the form C<v1.20.300.4000> is parsed as a dual-valued quantity.
+It has the string value of C<"\x{1}\x{14}\x{12c}\x{fa0}"> (i.e., a UTF-8
+string) and a numeric value of C<1 + 20/1000 + 300/1000000 + 4000/1000000000>.
+This is useful for representing Unicode strings, and for comparing version
+numbers using the string comparison operators, C<cmp>, C<gt>, C<lt> etc.
+
+Such "version tuples" or "vectors" are accepted by both C<require> and
+C<use>. The C<$^V> variable contains the running Perl interpreter's
+version in this format. See L<perlvar/$^V>.
+
=head2 Integer Arithmetic
By default, Perl assumes that it must do most of its arithmetic in
The non-standard modules SSLeay::BN and Math::Pari provide
equivalent functionality (and much more) with a substantial
performance savings.
+
+=cut