=head2 Why do regex character classes sometimes match only in the ASCII range?
-=head2 Why do some characters not uppercase or lowercase correctly?
-
-It seemed like a good idea at the time, to keep the semantics the same for
-standard strings, when Perl got Unicode support. The plan is to fix this
-in the future, and the casing component has in fact mostly been fixed, but we
-have to deal with the fact that Perl treats equal strings differently,
-depending on the internal state.
-
-First the casing. Just put a C<use feature 'unicode_strings'> near the
-beginning of your program. Within its lexical scope, C<uc>, C<lc>, C<ucfirst>,
-C<lcfirst>, and the regular expression escapes C<\U>, C<\L>, C<\u>, C<\l> use
-Unicode semantics for changing case regardless of whether the UTF8 flag is on
-or not. However, if you pass strings to subroutines in modules outside the
-pragma's scope, they currently likely won't behave this way, and you have to
-try one of the solutions below. There is another exception as well: if you
-have furnished your own casing functions to override the default, these will
-not be called unless the UTF8 flag is on)
-
-This remains a problem for the regular expression constructs
-C</.../i>, C<(?i:...)>, and C</[[:posix:]]/>.
-
-To force Unicode semantics, you can upgrade the internal representation to
-by doing C<utf8::upgrade($string)>. This can be used
+Starting in Perl 5.14 (and partially in Perl 5.12), just put a
+C<use feature 'unicode_strings'> near the beginning of your program.
+Within its lexical scope you shouldn't have this problem. It also is
+automatically enabled under C<use feature ':5.12'> or C<use v5.12> or
+using C<-E> on the command line for Perl 5.12 or higher.
+
+The rationale for requiring this is to not break older programs that
+rely on the way things worked before Unicode came along. Those older
+programs knew only about the ASCII character set, and so may not work
+properly for additional characters. When a string is encoded in UTF-8,
+Perl assumes that the program is prepared to deal with Unicode, but when
+the string isn't, Perl assumes that only ASCII
+is wanted, and so those characters that are not ASCII
+characters aren't recognized as to what they would be in Unicode.
+C<use feature 'unicode_strings'> tells Perl to treat all characters as
+Unicode, whether the string is encoded in UTF-8 or not, thus avoiding
+the problem.
+
+However, on earlier Perls, or if you pass strings to subroutines outside
+the feature's scope, you can force Unicode rules by changing the
+encoding to UTF-8 by doing C<utf8::upgrade($string)>. This can be used
safely on any string, as it checks and does not change strings that have
already been upgraded.
For a more detailed discussion, see L<Unicode::Semantics> on CPAN.
+=head2 Why do some characters not uppercase or lowercase correctly?
+
+See the answer to the previous question.
+
=head2 How can I determine if a string is a text string or a binary string?
You can't. Some use the UTF8 flag for this, but that's misuse, and makes well
=head2 What is a "wide character"?
-This is a term used both for characters with an ordinal value greater than 127,
-characters with an ordinal value greater than 255, or any character occupying
-more than one byte, depending on the context.
+This is a term used for characters occupying more than one byte.
-The Perl warning "Wide character in ..." is caused by a character with an
-ordinal value greater than 255. With no specified encoding layer, Perl tries to
-fit things in ISO-8859-1 for backward compatibility reasons. When it can't, it
-emits this warning (if warnings are enabled), and outputs UTF-8 encoded data
+The Perl warning "Wide character in ..." is caused by such a character.
+With no specified encoding layer, Perl tries to
+fit things into a single byte. When it can't, it
+emits this warning (if warnings are enabled), and uses UTF-8 encoded data
instead.
To avoid this warning and to avoid having different output encodings in a single
but this is considered bad style. Especially C<_utf8_on> can be dangerous, for
the same reason that C<:utf8> can.
-There are some shortcuts for oneliners; see C<-C> in L<perlrun>.
+There are some shortcuts for oneliners;
+see L<-C|perlrun/-C [numberE<sol>list]> in L<perlrun>.
=head2 What's the difference between C<UTF-8> and C<utf8>?
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