X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/376d9008a264d010f49fb171a6506ba64f2cb864..fc273927378ed6a1a60a5758f7e36713630d5e13:/pod/perluniintro.pod

diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod
index e665d1a..beccd3c 100644
--- a/pod/perluniintro.pod
+++ b/pod/perluniintro.pod
@@ -5,39 +5,42 @@ perluniintro - Perl Unicode introduction
 =head1 DESCRIPTION
 
 This document gives a general idea of Unicode and how to use Unicode
-in Perl.
+in Perl.  See L</Further Resources> for references to more in-depth
+treatments of Unicode.
 
 =head2 Unicode
 
 Unicode is a character set standard which plans to codify all of the
 writing systems of the world, plus many other symbols.
 
-Unicode and ISO/IEC 10646 are coordinated standards that provide code
-points for characters in almost all modern character set standards,
-covering more than 30 writing systems and hundreds of languages,
+Unicode and ISO/IEC 10646 are coordinated standards that unify
+almost all other modern character set standards,
+covering more than 80 writing systems and hundreds of languages,
 including all commercially-important modern languages.  All characters
 in the largest Chinese, Japanese, and Korean dictionaries are also
 encoded. The standards will eventually cover almost all characters in
 more than 250 writing systems and thousands of languages.
+Unicode 1.0 was released in October 1991, and 6.0 in October 2010.
 
 A Unicode I<character> is an abstract entity.  It is not bound to any
 particular integer width, especially not to the C language C<char>.
 Unicode is language-neutral and display-neutral: it does not encode the
-language of the text and it does not define fonts or other graphical
+language of the text, and it does not generally define fonts or other graphical
 layout details.  Unicode operates on characters and on text built from
 those characters.
 
 Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
 SMALL LETTER ALPHA> and unique numbers for the characters, in this
 case 0x0041 and 0x03B1, respectively.  These unique numbers are called
-I<code points>.
+I<code points>.  A code point is essentially the position of the
+character within the set of all possible Unicode characters, and thus in
+Perl, the term I<ordinal> is often used interchangeably with it.
 
 The Unicode standard prefers using hexadecimal notation for the code
-points.  If numbers like "C<0x0041" are unfamiliar to
-you, take a peek at a later section, L</"Hexadecimal Notation">.
-The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>,
-to give the hexadecimal code point and the normative name of
-the character.
+points.  If numbers like C<0x0041> are unfamiliar to you, take a peek
+at a later section, L</"Hexadecimal Notation">.  The Unicode standard
+uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the
+hexadecimal code point and the normative name of the character.
 
 Unicode also defines various I<properties> for the characters, like
 "uppercase" or "lowercase", "decimal digit", or "punctuation";
@@ -45,101 +48,139 @@ these properties are independent of the names of the characters.
 Furthermore, various operations on the characters like uppercasing,
 lowercasing, and collating (sorting) are defined.
 
-A Unicode character consists either of a single code point, or a
-I<base character> (like C<LATIN CAPITAL LETTER A>), followed by one or
-more I<modifiers> (like C<COMBINING ACUTE ACCENT>).  This sequence of
+A Unicode I<logical> "character" can actually consist of more than one internal
+I<actual> "character" or code point.  For Western languages, this is adequately
+modelled by a I<base character> (like C<LATIN CAPITAL LETTER A>) followed
+by one or more I<modifiers> (like C<COMBINING ACUTE ACCENT>).  This sequence of
 base character and modifiers is called a I<combining character
-sequence>.
-
-Whether to call these combining character sequences "characters"
-depends on your point of view. If you are a programmer, you probably
-would tend towards seeing each element in the sequences as one unit,
-or "character".  The whole sequence could be seen as one "character",
-however, from the user's point of view, since that's probably what it
-looks like in the context of the user's language.
-
-With this "whole sequence" view of characters, the total number of
-characters is open-ended. But in the programmer's "one unit is one
-character" point of view, the concept of "characters" is more
-deterministic.  In this document, we take that second  point of view: one
-"character" is one Unicode code point, be it a base character or a
-combining character.
-
-For some combinations, there are I<precomposed> characters.
-C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as
-a single code point.  These precomposed characters are, however,
-only available for some combinations, and are mainly
-meant to support round-trip conversions between Unicode and legacy
-standards (like the ISO 8859).  In the general case, the composing
-method is more extensible.  To support conversion between
-different compositions of the characters, various I<normalization
-forms> to standardize representations are also defined.
+sequence>.  Some non-western languages require more complicated
+models, so Unicode created the I<grapheme cluster> concept, which was
+later further refined into the I<extended grapheme cluster>.  For
+example, a Korean Hangul syllable is considered a single logical
+character, but most often consists of three actual
+Unicode characters: a leading consonant followed by an interior vowel followed
+by a trailing consonant.
+
+Whether to call these extended grapheme clusters "characters" depends on your
+point of view. If you are a programmer, you probably would tend towards seeing
+each element in the sequences as one unit, or "character".  However from
+the user's point of view, the whole sequence could be seen as one
+"character" since that's probably what it looks like in the context of the
+user's language.  In this document, we take the programmer's point of
+view: one "character" is one Unicode code point.
+
+For some combinations of base character and modifiers, there are
+I<precomposed> characters.  There is a single character equivalent, for
+example, for the sequence C<LATIN CAPITAL LETTER A> followed by
+C<COMBINING ACUTE ACCENT>.  It is called  C<LATIN CAPITAL LETTER A WITH
+ACUTE>.  These precomposed characters are, however, only available for
+some combinations, and are mainly meant to support round-trip
+conversions between Unicode and legacy standards (like ISO 8859).  Using
+sequences, as Unicode does, allows for needing fewer basic building blocks
+(code points) to express many more potential grapheme clusters.  To
+support conversion between equivalent forms, various I<normalization
+forms> are also defined.  Thus, C<LATIN CAPITAL LETTER A WITH ACUTE> is
+in I<Normalization Form Composed>, (abbreviated NFC), and the sequence
+C<LATIN CAPITAL LETTER A> followed by C<COMBINING ACUTE ACCENT>
+represents the same character in I<Normalization Form Decomposed> (NFD).
 
 Because of backward compatibility with legacy encodings, the "a unique
 number for every character" idea breaks down a bit: instead, there is
 "at least one number for every character".  The same character could
 be represented differently in several legacy encodings.  The
-converse is also not true: some code points do not have an assigned
+converse is not true: some code points do not have an assigned
 character.  Firstly, there are unallocated code points within
 otherwise used blocks.  Secondly, there are special Unicode control
 characters that do not represent true characters.
 
-A common myth about Unicode is that it would be "16-bit", that is,
-Unicode is only represented as C<0x10000> (or 65536) characters from
-C<0x0000> to C<0xFFFF>.  B<This is untrue.> Since Unicode 2.0, Unicode
-has been defined all the way up to 21 bits (C<0x10FFFF>), and since
-Unicode 3.1, characters have been defined beyond C<0xFFFF>.  The first
-C<0x10000> characters are called the I<Plane 0>, or the I<Basic
-Multilingual Plane> (BMP).  With Unicode 3.1, 17 planes in all are
-defined--but nowhere near full of defined characters, yet.
-
-Another myth is that the 256-character blocks have something to do
-with languages--that each languages is specified inside a block.
-B<This is also untrue.> The division into blocks exists, but it is
-almost completely accidental--an artifact of how the characters have
-been historically allocated.  Instead, there is a concept called
-I<scripts>, which is more useful: there is C<Latin> script,
-C<Greek> script, and so on.  Scripts usually span varied parts of
-several blocks.  For further information see L<Unicode::UCD>.
+When Unicode was first conceived, it was thought that all the world's
+characters could be represented using a 16-bit word; that is a maximum of
+C<0x10000> (or 65,536) characters would be needed, from C<0x0000> to
+C<0xFFFF>.  This soon proved to be wrong, and since Unicode 2.0 (July
+1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>),
+and Unicode 3.1 (March 2001) defined the first characters above C<0xFFFF>.
+The first C<0x10000> characters are called the I<Plane 0>, or the
+I<Basic Multilingual Plane> (BMP).  With Unicode 3.1, 17 (yes,
+seventeen) planes in all were defined--but they are nowhere near full of
+defined characters, yet.
+
+When a new language is being encoded, Unicode generally will choose a
+C<block> of consecutive unallocated code points for its characters.  So
+far, the number of code points in these blocks has always been evenly
+divisible by 16.  Extras in a block, not currently needed, are left
+unallocated, for future growth.  But there have been occasions when
+a later release needed more code points than the available extras, and a
+new block had to allocated somewhere else, not contiguous to the initial
+one, to handle the overflow.  Thus, it became apparent early on that
+"block" wasn't an adequate organizing principle, and so the C<Script>
+property was created.  (Later an improved script property was added as
+well, the C<Script_Extensions> property.)  Those code points that are in
+overflow blocks can still
+have the same script as the original ones.  The script concept fits more
+closely with natural language: there is C<Latin> script, C<Greek>
+script, and so on; and there are several artificial scripts, like
+C<Common> for characters that are used in multiple scripts, such as
+mathematical symbols.  Scripts usually span varied parts of several
+blocks.  For more information about scripts, see L<perlunicode/Scripts>.
+The division into blocks exists, but it is almost completely
+accidental--an artifact of how the characters have been and still are
+allocated.  (Note that this paragraph has oversimplified things for the
+sake of this being an introduction.  Unicode doesn't really encode
+languages, but the writing systems for them--their scripts; and one
+script can be used by many languages.  Unicode also encodes things that
+aren't really about languages, such as symbols like C<BAGGAGE CLAIM>.)
 
 The Unicode code points are just abstract numbers.  To input and
-output these abstract numbers, the numbers must be I<encoded> somehow.
-Unicode defines several I<character encoding forms>, of which I<UTF-8>
-is perhaps the most popular.  UTF-8 is a variable length encoding that
-encodes Unicode characters as 1 to 6 bytes (only 4 with the currently
-defined characters).  Other encodings include UTF-16 and UTF-32 and their
-big- and little-endian variants (UTF-8 is byte-order independent).
-The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms.
+output these abstract numbers, the numbers must be I<encoded> or
+I<serialised> somehow.  Unicode defines several I<character encoding
+forms>, of which I<UTF-8> is the most popular.  UTF-8 is a
+variable length encoding that encodes Unicode characters as 1 to 4
+bytes.  Other encodings
+include UTF-16 and UTF-32 and their big- and little-endian variants
+(UTF-8 is byte-order independent).  The ISO/IEC 10646 defines the UCS-2
+and UCS-4 encoding forms.
 
 For more information about encodings--for instance, to learn what
 I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
 
 =head2 Perl's Unicode Support
 
-Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode
-natively.  Perl 5.8.0, however, is the first recommended release for
+Starting from Perl v5.6.0, Perl has had the capacity to handle Unicode
+natively.  Perl v5.8.0, however, is the first recommended release for
 serious Unicode work.  The maintenance release 5.6.1 fixed many of the
 problems of the initial Unicode implementation, but for example
-regular expressions did not really work with Unicode.
-
-B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer
-necessary.> In earlier releases the C<utf8> pragma was used to declare
+regular expressions still do not work with Unicode in 5.6.1.
+Perl v5.14.0 is the first release where Unicode support is
+(almost) seamlessly integrable without some gotchas (the exception being
+some differences in L<quotemeta|perlfunc/quotemeta>, and that is fixed
+starting in Perl 5.16.0).   To enable this
+seamless support, you should C<use feature 'unicode_strings'> (which is
+automatically selected if you C<use 5.012> or higher).  See L<feature>.
+(5.14 also fixes a number of bugs and departures from the Unicode
+standard.)
+
+Before Perl v5.8.0, the use of C<use utf8> was used to declare
 that operations in the current block or file would be Unicode-aware.
 This model was found to be wrong, or at least clumsy: the "Unicodeness"
-is now carried with the data instead of being attached to the
-operations.  Only one case remains where an explicit C<use utf8> is
-needed: if your Perl script itself is encoded in UTF-8, you can use
-UTF-8 in your identifier names, and in string and regular expression
+is now carried with the data, instead of being attached to the
+operations.
+Starting with Perl v5.8.0, only one case remains where an explicit C<use
+utf8> is needed: if your Perl script itself is encoded in UTF-8, you can
+use UTF-8 in your identifier names, and in string and regular expression
 literals, by saying C<use utf8>.  This is not the default because
-scripts with legacy 8-bit data in them would break.
+scripts with legacy 8-bit data in them would break.  See L<utf8>.
 
 =head2 Perl's Unicode Model
 
 Perl supports both pre-5.6 strings of eight-bit native bytes, and
-strings of Unicode characters.  The principle is that Perl tries to
-keep its data as eight-bit bytes for as long as possible, but as soon
+strings of Unicode characters.  The general principle is that Perl tries
+to keep its data as eight-bit bytes for as long as possible, but as soon
 as Unicodeness cannot be avoided, the data is transparently upgraded
-to Unicode.
+to Unicode.  Prior to Perl v5.14.0, the upgrade was not completely
+transparent (see L<perlunicode/The "Unicode Bug">), and for backwards
+compatibility, full transparency is not gained unless C<use feature
+'unicode_strings'> (see L<feature>) or C<use 5.012> (or higher) is
+selected.
 
 Internally, Perl currently uses either whatever the native eight-bit
 character set of the platform (for example Latin-1) is, defaulting to
@@ -149,101 +190,138 @@ character set.  Otherwise, it uses UTF-8.
 
 A user of Perl does not normally need to know nor care how Perl
 happens to encode its internal strings, but it becomes relevant when
-outputting Unicode strings to a stream without a discipline--one with
-the "default" encoding.  In such a case, the raw bytes used internally
+outputting Unicode strings to a stream without a PerlIO layer (one with
+the "default" encoding).  In such a case, the raw bytes used internally
 (the native character set or UTF-8, as appropriate for each string)
 will be used, and a "Wide character" warning will be issued if those
 strings contain a character beyond 0x00FF.
 
 For example,
 
-      perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'              
+      perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
 
 produces a fairly useless mixture of native bytes and UTF-8, as well
-as a warning.
+as a warning:
+
+     Wide character in print at ...
 
-To output UTF-8 always, use the "C<:utf8>" output discipline.  Prepending
+To output UTF-8, use the C<:encoding> or C<:utf8> output layer.  Prepending
 
       binmode(STDOUT, ":utf8");
 
 to this sample program ensures that the output is completely UTF-8,
-and helpfully removes the program's warning.
+and removes the program's warning.
+
+You can enable automatic UTF-8-ification of your standard file
+handles, default C<open()> layer, and C<@ARGV> by using either
+the C<-C> command line switch or the C<PERL_UNICODE> environment
+variable, see L<perlrun> for the documentation of the C<-C> switch.
+
+Note that this means that Perl expects other software to work the same
+way:
+if Perl has been led to believe that STDIN should be UTF-8, but then
+STDIN coming in from another command is not UTF-8, Perl will likely
+complain about the malformed UTF-8.
 
-If your locale environment variables (C<LANGUAGE>, C<LC_ALL>,
-C<LC_CTYPE>, C<LANG>) contain the strings 'UTF-8' or 'UTF8',
-regardless of case, then the default encoding of your STDIN, STDOUT,
-and STDERR and of B<any subsequent file open>, is UTF-8.  Note that
-this means that Perl expects other software to work, too: if STDIN
-coming in from another command is not UTF-8, Perl will complain about
-malformed UTF-8.
+All features that combine Unicode and I/O also require using the new
+PerlIO feature.  Almost all Perl 5.8 platforms do use PerlIO, though:
+you can see whether yours is by running "perl -V" and looking for
+C<useperlio=define>.
 
 =head2 Unicode and EBCDIC
 
-Perl 5.8.0 also supports Unicode on EBCDIC platforms.  There,
-Unicode support is somewhat more complex to implement since
-additional conversions are needed at every step.  Some problems
-remain, see L<perlebcdic> for details.
+Perl 5.8.0 added support for Unicode on EBCDIC platforms.  This support
+was allowed to lapse in later releases, but was revived in 5.22.
+Unicode support is somewhat more complex to implement since additional
+conversions are needed.  See L<perlebcdic> for more information.
 
-In any case, the Unicode support on EBCDIC platforms is better than
-in the 5.6 series, which didn't work much at all for EBCDIC platform.
 On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
 instead of UTF-8.  The difference is that as UTF-8 is "ASCII-safe" in
 that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
-"EBCDIC-safe".
+"EBCDIC-safe", in that all the basic characters (which includes all
+those that have ASCII equivalents (like C<"A">, C<"0">, C<"%">, I<etc.>)
+are the same in both EBCDIC and UTF-EBCDIC.  Often, documentation
+will use the term "UTF-8" to mean UTF-EBCDIC as well.  This is the case
+in this document.
 
 =head2 Creating Unicode
 
-To create Unicode characters in literals for code points above C<0xFF>,
-use the C<\x{...}> notation in double-quoted strings:
+This section applies fully to Perls starting with v5.22.  Various
+caveats for earlier releases are in the L</Earlier releases caveats>
+subsection below.
 
-    my $smiley = "\x{263a}";
+To create Unicode characters in literals,
+use the C<\N{...}> notation in double-quoted strings:
 
-Similarly, it can be used in regular expression literals
+ my $smiley_from_name = "\N{WHITE SMILING FACE}";
+ my $smiley_from_code_point = "\N{U+263a}";
 
-    $smiley =~ /\x{263a}/;
+Similarly, they can be used in regular expression literals
 
-At run-time you can use C<chr()>:
+ $smiley =~ /\N{WHITE SMILING FACE}/;
+ $smiley =~ /\N{U+263a}/;
 
-    my $hebrew_alef = chr(0x05d0);
+At run-time you can use:
 
-See L</"Further Resources"> for how to find all these numeric codes.
+ use charnames ();
+ my $hebrew_alef_from_name
+                      = charnames::string_vianame("HEBREW LETTER ALEF");
+ my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");
 
 Naturally, C<ord()> will do the reverse: it turns a character into
 a code point.
 
-Note that C<\x..> (no C<{}> and only two hexadecimal digits),
-C<\x{...}>, and C<chr(...)> for arguments less than C<0x100> (decimal
-256) generate an eight-bit character for backward compatibility with
-older Perls.  For arguments of C<0x100> or more, Unicode characters are
-always produced. If you want to force the production of Unicode
-characters regardless of the numeric value, use C<pack("U", ...)>
-instead of C<\x..>, C<\x{...}>, or C<chr()>.
+There are other runtime options as well.  You can use C<pack()>:
+
+ my $hebrew_alef_from_code_point = pack("U", 0x05d0);
+
+Or you can use C<chr()>, though it is less convenient in the general
+case:
+
+ $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
+ utf8::upgrade($hebrew_alef_from_code_point);
 
-You can also use the C<charnames> pragma to invoke characters
-by name in double-quoted strings:
+The C<utf8::unicode_to_native()> and C<utf8::upgrade()> aren't needed if
+the argument is above 0xFF, so the above could have been written as
 
-    use charnames ':full';
-    my $arabic_alef = "\N{ARABIC LETTER ALEF}";
+ $hebrew_alef_from_code_point = chr(0x05d0);
 
-And, as mentioned above, you can also C<pack()> numbers into Unicode
-characters:
+since 0x5d0 is above 255.
 
-   my $georgian_an  = pack("U", 0x10a0);
+C<\x{}> and C<\o{}> can also be used to specify code points at compile
+time in double-quotish strings, but, for backward compatibility with
+older Perls, the same rules apply as with C<chr()> for code points less
+than 256.
 
-Note that both C<\x{...}> and C<\N{...}> are compile-time string
-constants: you cannot use variables in them.  if you want similar
-run-time functionality, use C<chr()> and C<charnames::vianame()>.
+C<utf8::unicode_to_native()> is used so that the Perl code is portable
+to EBCDIC platforms.  You can omit it if you're I<really> sure no one
+will ever want to use your code on a non-ASCII platform.  Starting in
+Perl v5.22, calls to it on ASCII platforms are optimized out, so there's
+no performance penalty at all in adding it.  Or you can simply use the
+other constructs that don't require it.
 
-Also note that if all the code points for pack "U" are below 0x100,
-bytes will be generated, just like if you were using C<chr()>.
+See L</"Further Resources"> for how to find all these names and numeric
+codes.
 
-   my $bytes = pack("U*", 0x80, 0xFF);
+=head3 Earlier releases caveats
 
-If you want to force the result to Unicode characters, use the special
-C<"U0"> prefix.  It consumes no arguments but forces the result to be
-in Unicode characters, instead of bytes.
+On EBCDIC platforms, prior to v5.22, using C<\N{U+...}> doesn't work
+properly.
 
-   my $chars = pack("U0U*", 0x80, 0xFF);
+Prior to v5.16, using C<\N{...}> with a character name (as opposed to a
+C<U+...> code point) required a S<C<use charnames :full>>.
+
+Prior to v5.14, there were some bugs in C<\N{...}> with a character name
+(as opposed to a C<U+...> code point).
+
+C<charnames::string_vianame()> was introduced in v5.14.  Prior to that,
+C<charnames::vianame()> should work, but only if the argument is of the
+form C<"U+...">.  Your best bet there for runtime Unicode by character
+name is probably:
+
+ use charnames ();
+ my $hebrew_alef_from_name
+                  = pack("U", charnames::vianame("HEBREW LETTER ALEF"));
 
 =head2 Handling Unicode
 
@@ -252,43 +330,31 @@ strings as usual.  Functions like C<index()>, C<length()>, and
 C<substr()> will work on the Unicode characters; regular expressions
 will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
 
-Note that Perl considers combining character sequences
-to be characters, so for example
+Note that Perl considers grapheme clusters to be separate characters, so for
+example
 
-    use charnames ':full';
-    print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
+ print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"),
+       "\n";
 
 will print 2, not 1.  The only exception is that regular expressions
-have C<\X> for matching a combining character sequence.
+have C<\X> for matching an extended grapheme cluster.  (Thus C<\X> in a
+regular expression would match the entire sequence of both the example
+characters.)
 
 Life is not quite so transparent, however, when working with legacy
 encodings, I/O, and certain special cases:
 
 =head2 Legacy Encodings
 
-When you combine legacy data and Unicode the legacy data needs
-to be upgraded to Unicode.  Normally ISO 8859-1 (or EBCDIC, if
-applicable) is assumed.  You can override this assumption by
-using the C<encoding> pragma, for example
-
-    use encoding 'latin2'; # ISO 8859-2
-
-in which case literals (string or regular expressions), C<chr()>, and
-C<ord()> in your whole script are assumed to produce Unicode
-characters from ISO 8859-2 code points.  Note that the matching for
-encoding names is forgiving: instead of C<latin2> you could have
-said C<Latin 2>, or C<iso8859-2>, or other variations.  With just
-
-    use encoding;
-
-the environment variable C<PERL_ENCODING> will be consulted.
-If that variable isn't set, the encoding pragma will fail.
+When you combine legacy data and Unicode, the legacy data needs
+to be upgraded to Unicode.  Normally the legacy data is assumed to be
+ISO 8859-1 (or EBCDIC, if applicable).
 
 The C<Encode> module knows about many encodings and has interfaces
 for doing conversions between those encodings:
 
-    use Encode 'from_to';
-    from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
+    use Encode 'decode';
+    $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
 
 =head2 Unicode I/O
 
@@ -319,9 +385,12 @@ and on already open streams, use C<binmode()>:
     binmode(STDOUT, ":encoding(shift_jis)");
 
 The matching of encoding names is loose: case does not matter, and
-many encodings have several aliases.  Note that C<:utf8> discipline
-must always be specified exactly like that; it is I<not> subject to the
-loose matching of encoding names.
+many encodings have several aliases.  Note that the C<:utf8> layer
+must always be specified exactly like that; it is I<not> subject to
+the loose matching of encoding names. Also note that currently C<:utf8> is unsafe for
+input, because it accepts the data without validating that it is indeed valid
+UTF-8; you should instead use C<:encoding(utf-8)> (with or without a
+hyphen).
 
 See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
 L<Encode::PerlIO> for the C<:encoding()> layer, and
@@ -329,20 +398,21 @@ L<Encode::Supported> for many encodings supported by the C<Encode>
 module.
 
 Reading in a file that you know happens to be encoded in one of the
-Unicode encodings does not magically turn the data into Unicode in
-Perl's eyes.  To do that, specify the appropriate discipline when
-opening files
+Unicode or legacy encodings does not magically turn the data into
+Unicode in Perl's eyes.  To do that, specify the appropriate
+layer when opening files
 
-    open(my $fh,'<:utf8', 'anything');
+    open(my $fh,'<:encoding(utf8)', 'anything');
     my $line_of_unicode = <$fh>;
 
     open(my $fh,'<:encoding(Big5)', 'anything');
     my $line_of_unicode = <$fh>;
 
-The I/O disciplines can also be specified more flexibly with
+The I/O layers can also be specified more flexibly with
 the C<open> pragma.  See L<open>, or look at the following example.
 
-    use open ':utf8'; # input and output default discipline will be UTF-8
+    use open ':encoding(utf8)'; # input/output default encoding will be
+                                # UTF-8
     open X, ">file";
     print X chr(0x100), "\n";
     close X;
@@ -350,10 +420,11 @@ the C<open> pragma.  See L<open>, or look at the following example.
     printf "%#x\n", ord(<Y>); # this should print 0x100
     close Y;
 
-With the C<open> pragma you can use the C<:locale> discipline
+With the C<open> pragma you can use the C<:locale> layer
 
-    $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
-    # the :locale will probe the locale environment variables like LC_ALL
+    BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
+    # the :locale will probe the locale environment variables like
+    # LC_ALL
     use open OUT => ':locale'; # russki parusski
     open(O, ">koi8");
     print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
@@ -362,97 +433,96 @@ With the C<open> pragma you can use the C<:locale> discipline
     printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
     close I;
 
-or you can also use the C<':encoding(...)'> discipline
-
-    open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
-    my $line_of_unicode = <$epic>;
-
 These methods install a transparent filter on the I/O stream that
 converts data from the specified encoding when it is read in from the
 stream.  The result is always Unicode.
 
 The L<open> pragma affects all the C<open()> calls after the pragma by
-setting default disciplines.  If you want to affect only certain
-streams, use explicit disciplines directly in the C<open()> call.
+setting default layers.  If you want to affect only certain
+streams, use explicit layers directly in the C<open()> call.
 
 You can switch encodings on an already opened stream by using
 C<binmode()>; see L<perlfunc/binmode>.
 
-The C<:locale> does not currently (as of Perl 5.8.0) work with
+The C<:locale> does not currently work with
 C<open()> and C<binmode()>, only with the C<open> pragma.  The
 C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
 C<binmode()>, and the C<open> pragma.
 
-Similarly, you may use these I/O disciplines on output streams to
+Similarly, you may use these I/O layers on output streams to
 automatically convert Unicode to the specified encoding when it is
 written to the stream. For example, the following snippet copies the
 contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
 the file "text.utf8", encoded as UTF-8:
 
-    open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
-    open(my $unicode, '>:utf8',                 'text.utf8');
-    while (<$nihongo>) { print $unicode }
+    open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
+    open(my $unicode, '>:utf8',                  'text.utf8');
+    while (<$nihongo>) { print $unicode $_ }
 
 The naming of encodings, both by the C<open()> and by the C<open>
-pragma, is similar to the C<encoding> pragma in that it allows for
-flexible names: C<koi8-r> and C<KOI8R> will both be understood.
+pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
+understood.
 
 Common encodings recognized by ISO, MIME, IANA, and various other
 standardisation organisations are recognised; for a more detailed
-list see L<Encode>.
+list see L<Encode::Supported>.
 
 C<read()> reads characters and returns the number of characters.
 C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
 and C<sysseek()>.
 
 Notice that because of the default behaviour of not doing any
-conversion upon input if there is no default discipline,
+conversion upon input if there is no default layer,
 it is easy to mistakenly write code that keeps on expanding a file
-by repeatedly encoding:
+by repeatedly encoding the data:
 
     # BAD CODE WARNING
     open F, "file";
     local $/; ## read in the whole file of 8-bit characters
     $t = <F>;
     close F;
-    open F, ">:utf8", "file";
+    open F, ">:encoding(utf8)", "file";
     print F $t; ## convert to UTF-8 on output
     close F;
 
 If you run this code twice, the contents of the F<file> will be twice
-UTF-8 encoded.  A C<use open ':utf8'> would have avoided the bug, or
-explicitly opening also the F<file> for input as UTF-8.
+UTF-8 encoded.  A C<use open ':encoding(utf8)'> would have avoided the
+bug, or explicitly opening also the F<file> for input as UTF-8.
 
 B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
-Perl has been built with the new "perlio" feature.  Almost all 
-Perl 5.8 platforms do use "perlio", though: you can see whether
-yours is by running "perl -V" and looking for C<useperlio=define>.
+Perl has been built with L<PerlIO>, which is the default
+on most systems.
 
 =head2 Displaying Unicode As Text
 
 Sometimes you might want to display Perl scalars containing Unicode as
 simple ASCII (or EBCDIC) text.  The following subroutine converts
 its argument so that Unicode characters with code points greater than
-255 are displayed as "C<\x{...}>", control characters (like "C<\n>") are
-displayed as "C<\x..>", and the rest of the characters as themselves:
-
-   sub nice_string {
-       join("",
-         map { $_ > 255 ?                  # if wide character...
-               sprintf("\\x{%04X}", $_) :  # \x{...}
-               chr($_) =~ /[[:cntrl:]]/ ?  # else if control character ...
-               sprintf("\\x%02X", $_) :    # \x..
-               chr($_)                     # else as themselves
-         } unpack("U*", $_[0]));           # unpack Unicode characters
+255 are displayed as C<\x{...}>, control characters (like C<\n>) are
+displayed as C<\x..>, and the rest of the characters as themselves:
+
+ sub nice_string {
+        join("",
+        map { $_ > 255                    # if wide character...
+              ? sprintf("\\x{%04X}", $_)  # \x{...}
+              : chr($_) =~ /[[:cntrl:]]/  # else if control character...
+                ? sprintf("\\x%02X", $_)  # \x..
+                : quotemeta(chr($_))      # else quoted or as themselves
+        } unpack("W*", $_[0]));           # unpack Unicode characters
    }
 
 For example,
 
    nice_string("foo\x{100}bar\n")
 
-returns:
+returns the string
+
+   'foo\x{0100}bar\x0A'
 
-   "foo\x{0100}bar\x0A"
+which is ready to be printed.
+
+(C<\\x{}> is used here instead of C<\\N{}>, since it's most likely that
+you want to see what the native values are.)
 
 =head2 Special Cases
 
@@ -462,13 +532,13 @@ returns:
 
 Bit Complement Operator ~ And vec()
 
-The bit complement operator C<~> may produce surprising results if used on
-strings containing characters with ordinal values above 255. In such a
-case, the results are consistent with the internal encoding of the
-characters, but not with much else. So don't do that. Similarly for C<vec()>:
-you will be operating on the internally-encoded bit patterns of the Unicode
-characters, not on the code point values, which is very probably not what
-you want.
+The bit complement operator C<~> may produce surprising results if
+used on strings containing characters with ordinal values above
+255. In such a case, the results are consistent with the internal
+encoding of the characters, but not with much else. So don't do
+that. Similarly for C<vec()>: you will be operating on the
+internally-encoded bit patterns of the Unicode characters, not on
+the code point values, which is very probably not what you want.
 
 =item *
 
@@ -477,23 +547,24 @@ Peeking At Perl's Internal Encoding
 Normal users of Perl should never care how Perl encodes any particular
 Unicode string (because the normal ways to get at the contents of a
 string with Unicode--via input and output--should always be via
-explicitly-defined I/O disciplines). But if you must, there are two
+explicitly-defined I/O layers). But if you must, there are two
 ways of looking behind the scenes.
 
 One way of peeking inside the internal encoding of Unicode characters
-is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)>
-to display the bytes:
+is to use C<unpack("C*", ...> to get the bytes of whatever the string
+encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
+UTF-8 encoding:
 
     # this prints  c4 80  for the UTF-8 bytes 0xc4 0x80
-    print join(" ", unpack("H*", pack("U", 0x100))), "\n";
+    print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
 
 Yet another way would be to use the Devel::Peek module:
 
     perl -MDevel::Peek -e 'Dump(chr(0x100))'
 
-That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
+That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
 and Unicode characters in C<PV>.  See also later in this document
-the discussion about the C<is_utf8> function of the C<Encode> module.
+the discussion about the C<utf8::is_utf8()> function.
 
 =back
 
@@ -514,17 +585,16 @@ C<LATIN CAPITAL LETTER A>?)
 The short answer is that by default Perl compares equivalence (C<eq>,
 C<ne>) based only on code points of the characters.  In the above
 case, the answer is no (because 0x00C1 != 0x0041).  But sometimes, any
-CAPITAL LETTER As should be considered equal, or even As of any case.
+CAPITAL LETTER A's should be considered equal, or even A's of any case.
 
 The long answer is that you need to consider character normalization
-and casing issues: see L<Unicode::Normalize>, Unicode Technical
-Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
-Mappings>, http://www.unicode.org/unicode/reports/tr15/ and 
-http://www.unicode.org/unicode/reports/tr21/ 
+and casing issues: see L<Unicode::Normalize>, Unicode Technical Report #15,
+L<Unicode Normalization Forms|http://www.unicode.org/unicode/reports/tr15> and
+sections on case mapping in the L<Unicode Standard|http://www.unicode.org>.
 
-As of Perl 5.8.0, regular expression case-ignoring matching
-implements only 1:1 semantics: one character matches one character.
-In I<Case Mappings> both 1:N and N:1 matches are defined.
+As of Perl 5.8.0, the "Full" case-folding of I<Case
+Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them,
+mostly fixed by 5.14, and essentially entirely by 5.18.
 
 =item *
 
@@ -538,13 +608,13 @@ C<LATIN CAPITAL LETTER A WITH GRAVE>?)
 
 The short answer is that by default, Perl compares strings (C<lt>,
 C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
-characters.  In the above case, the answer is "after", since C<0x00C1>
-> C<0x00C0>.
+characters.  In the above case, the answer is "after", since
+C<0x00C1> > C<0x00C0>.
 
 The long answer is that "it depends", and a good answer cannot be
 given without knowing (at the very least) the language context.
 See L<Unicode::Collate>, and I<Unicode Collation Algorithm>
-http://www.unicode.org/unicode/reports/tr10/
+L<http://www.unicode.org/unicode/reports/tr10/>
 
 =back
 
@@ -556,18 +626,28 @@ http://www.unicode.org/unicode/reports/tr10/
 
 Character Ranges and Classes
 
-Character ranges in regular expression character classes (C</[a-z]/>)
-and in the C<tr///> (also known as C<y///>) operator are not magically
-Unicode-aware.  What this means that C<[A-Za-z]> will not magically start
-to mean "all alphabetic letters"; not that it does mean that even for
-8-bit characters, you should be using C</[[:alpha:]]/> in that case.
+Character ranges in regular expression bracketed character classes ( e.g.,
+C</[a-z]/>) and in the C<tr///> (also known as C<y///>) operator are not
+magically Unicode-aware.  What this means is that C<[A-Za-z]> will not
+magically start to mean "all alphabetic letters" (not that it does mean that
+even for 8-bit characters; for those, if you are using locales (L<perllocale>),
+use C</[[:alpha:]]/>; and if not, use the 8-bit-aware property C<\p{alpha}>).
+
+All the properties that begin with C<\p> (and its inverse C<\P>) are actually
+character classes that are Unicode-aware.  There are dozens of them, see
+L<perluniprops>.
+
+Starting in v5.22, you can use Unicode code points as the end points of
+regular expression pattern character ranges, and the range will include
+all Unicode code points that lie between those end points, inclusive.
 
-For specifying character classes like that in regular expressions, you can use
-the various Unicode properties--C<\pL>, or perhaps C<\p{Alphabetic}>,
-in this particular case.  You can use Unicode code points as the end
-points of character ranges, but there is no magic associated with
-specifying a certain range.  For further information--there are dozens
-of Unicode character classes--see L<perlunicode>.
+ qr/ [\N{U+03]-\N{U+20}] /x
+
+includes the code points
+C<\N{U+03}>, C<\N{U+04}>, ..., C<\N{U+20}>.
+
+(It is planned to extend this behavior to ranges in C<tr///> in Perl
+v5.24.)
 
 =item *
 
@@ -576,7 +656,9 @@ String-To-Number Conversions
 Unicode does define several other decimal--and numeric--characters
 besides the familiar 0 to 9, such as the Arabic and Indic digits.
 Perl does not support string-to-number conversion for digits other
-than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
+than ASCII C<0> to C<9> (and ASCII C<a> to C<f> for hexadecimal).
+To get safe conversions from any Unicode string, use
+L<Unicode::UCD/num()>.
 
 =back
 
@@ -584,37 +666,43 @@ than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
 
 =over 4
 
-=item 
+=item *
 
 Will My Old Scripts Break?
 
 Very probably not.  Unless you are generating Unicode characters
-somehow, old behaviour should be preserved.  About the only
-behaviour that has changed and which could start generating Unicode
-is the old behaviour of C<chr()> where supplying an argument more
-than 255 produced a character modulo 255.  C<chr(300)>, for example,
-was equal to C<chr(45)>.
+somehow, old behaviour should be preserved.  About the only behaviour
+that has changed and which could start generating Unicode is the old
+behaviour of C<chr()> where supplying an argument more than 255
+produced a character modulo 255.  C<chr(300)>, for example, was equal
+to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
+BREVE.
 
-=item 
+=item *
 
 How Do I Make My Scripts Work With Unicode?
 
 Very little work should be needed since nothing changes until you
-generate Unicode data.  The trick is getting input as Unicode; for
-that, see the earlier I/O discussion.
+generate Unicode data.  The most important thing is getting input as
+Unicode; for that, see the earlier I/O discussion.
+To get full seamless Unicode support, add
+C<use feature 'unicode_strings'> (or C<use 5.012> or higher) to your
+script.
 
-=item 
+=item *
 
 How Do I Know Whether My String Is In Unicode?
 
-You shouldn't care.  No, you really shouldn't.  No, really.  If you have
-to care--beyond the cases described above--it means that we
-didn't get the transparency of Unicode quite right.
+You shouldn't have to care.  But you may if your Perl is before 5.14.0
+or you haven't specified C<use feature 'unicode_strings'> or C<use
+5.012> (or higher) because otherwise the rules for the code points
+in the range 128 to 255 are different depending on
+whether the string they are contained within is in Unicode or not.
+(See L<perlunicode/When Unicode Does Not Happen>.)
 
-Okay, if you insist:
+To determine if a string is in Unicode, use:
 
-    use Encode 'is_utf8';
-    print is_utf8($string) ? 1 : 0, "\n";
+    print utf8::is_utf8($string) ? 1 : 0, "\n";
 
 But note that this doesn't mean that any of the characters in the
 string are necessary UTF-8 encoded, or that any of the characters have
@@ -623,10 +711,10 @@ string has any characters at all.  All the C<is_utf8()> does is to
 return the value of the internal "utf8ness" flag attached to the
 C<$string>.  If the flag is off, the bytes in the scalar are interpreted
 as a single byte encoding.  If the flag is on, the bytes in the scalar
-are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
-points of the characters.  Bytes added to an UTF-8 encoded string are
-automatically upgraded to UTF-8.  If mixed non-UTF8 and UTF-8 scalars
-are merged (double-quoted interpolation, explicit concatenation, and
+are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded
+code points of the characters.  Bytes added to a UTF-8 encoded string are
+automatically upgraded to UTF-8.  If mixed non-UTF-8 and UTF-8 scalars
+are merged (double-quoted interpolation, explicit concatenation, or
 printf/sprintf parameter substitution), the result will be UTF-8 encoded
 as if copies of the byte strings were upgraded to UTF-8: for example,
 
@@ -634,70 +722,79 @@ as if copies of the byte strings were upgraded to UTF-8: for example,
     $b = "\x{100}";
     print "$a = $b\n";
 
-the output string will be UTF-8-encoded "C<ab\x80c\x{100}\n>", but note
-that C<$a> will stay byte-encoded.
+the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
+C<$a> will stay byte-encoded.
 
 Sometimes you might really need to know the byte length of a string
 instead of the character length. For that use either the
-C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
-defined function C<length()>:
+C<Encode::encode_utf8()> function or the C<bytes> pragma
+and the C<length()> function:
 
     my $unicode = chr(0x100);
     print length($unicode), "\n"; # will print 1
     require Encode;
-    print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
+    print length(Encode::encode_utf8($unicode)),"\n"; # will print 2
     use bytes;
-    print length($unicode), "\n"; # will also print 2 (the 0xC4 0x80 of the UTF-8)
+    print length($unicode), "\n"; # will also print 2
+                                  # (the 0xC4 0x80 of the UTF-8)
+    no bytes;
+
+=item *
 
-=item 
+How Do I Find Out What Encoding a File Has?
+
+You might try L<Encode::Guess>, but it has a number of limitations.
+
+=item *
 
 How Do I Detect Data That's Not Valid In a Particular Encoding?
 
 Use the C<Encode> package to try converting it.
 For example,
 
-    use Encode 'encode_utf8';
-    if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
-        # valid
+    use Encode 'decode_utf8';
+
+    if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
+        # $string is valid utf8
     } else {
-        # invalid
+        # $string is not valid utf8
     }
 
-For UTF-8 only, you can use:
+Or use C<unpack> to try decoding it:
 
     use warnings;
-    @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
+    @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
 
-If invalid, a C<Malformed UTF-8 character (byte 0x##) in
-unpack> warning is produced. The "U0" means "expect strictly UTF-8
-encoded Unicode".  Without that the C<unpack("U*", ...)>
-would accept also data like C<chr(0xFF>), similarly to the
-C<pack> as we saw earlier.
+If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
+"process the string character per character".  Without that, the
+C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
+string starts with C<U>) and it would return the bytes making up the UTF-8
+encoding of the target string, something that will always work.
 
-=item 
+=item *
 
 How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
 
 This probably isn't as useful as you might think.
 Normally, you shouldn't need to.
 
-In one sense, what you are asking doesn't make much sense: Encodings
+In one sense, what you are asking doesn't make much sense: encodings
 are for characters, and binary data are not "characters", so converting
 "data" into some encoding isn't meaningful unless you know in what
 character set and encoding the binary data is in, in which case it's
 not just binary data, now is it?
 
-If you have a raw sequence of bytes that you know should be interpreted via
-a particular encoding, you can use C<Encode>:
+If you have a raw sequence of bytes that you know should be
+interpreted via a particular encoding, you can use C<Encode>:
 
     use Encode 'from_to';
     from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
 
-The call to C<from_to()> changes the bytes in C<$data>, but nothing material
-about the nature of the string has changed as far as Perl is concerned.
-Both before and after the call, the string C<$data> contains just a bunch of
-8-bit bytes. As far as Perl is concerned, the encoding of the string
-remains as "system-native 8-bit bytes".
+The call to C<from_to()> changes the bytes in C<$data>, but nothing
+material about the nature of the string has changed as far as Perl is
+concerned.  Both before and after the call, the string C<$data>
+contains just a bunch of 8-bit bytes. As far as Perl is concerned,
+the encoding of the string remains as "system-native 8-bit bytes".
 
 You might relate this to a fictional 'Translate' module:
 
@@ -707,15 +804,15 @@ You might relate this to a fictional 'Translate' module:
    ## phrase now contains "Ja"
 
 The contents of the string changes, but not the nature of the string.
-Perl doesn't know any more after the call than before that the contents
-of the string indicates the affirmative.
+Perl doesn't know any more after the call than before that the
+contents of the string indicates the affirmative.
 
 Back to converting data.  If you have (or want) data in your system's
 native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
 pack/unpack to convert to/from Unicode.
 
-    $native_string  = pack("C*", unpack("U*", $Unicode_string));
-    $Unicode_string = pack("U*", unpack("C*", $native_string));
+    $native_string  = pack("W*", unpack("U*", $Unicode_string));
+    $Unicode_string = pack("U*", unpack("W*", $native_string));
 
 If you have a sequence of bytes you B<know> is valid UTF-8,
 but Perl doesn't know it yet, you can make Perl a believer, too:
@@ -723,25 +820,46 @@ but Perl doesn't know it yet, you can make Perl a believer, too:
     use Encode 'decode_utf8';
     $Unicode = decode_utf8($bytes);
 
-You can convert well-formed UTF-8 to a sequence of bytes, but if
-you just want to convert random binary data into UTF-8, you can't.
-Any random collection of bytes isn't well-formed UTF-8.  You can
-use C<unpack("C*", $string)> for the former, and you can create
-well-formed Unicode data by C<pack("U*", 0xff, ...)>.
+or:
+
+    $Unicode = pack("U0a*", $bytes);
 
-=item 
+You can find the bytes that make up a UTF-8 sequence with
+
+    @bytes = unpack("C*", $Unicode_string)
+
+and you can create well-formed Unicode with
+
+    $Unicode_string = pack("U*", 0xff, ...)
+
+=item *
 
 How Do I Display Unicode?  How Do I Input Unicode?
 
-See http://www.alanwood.net/unicode/ and
-http://www.cl.cam.ac.uk/~mgk25/unicode.html
+See L<http://www.alanwood.net/unicode/> and
+L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
 
-=item 
+=item *
 
 How Does Unicode Work With Traditional Locales?
 
-In Perl, not very well.  Avoid using locales through the C<locale>
-pragma.  Use only one or the other.
+If your locale is a UTF-8 locale, starting in Perl v5.20, Perl works
+well for all categories except C<LC_COLLATE> dealing with sorting and
+the C<cmp> operator.
+
+For other locales, starting in Perl 5.16, you can specify
+
+    use locale ':not_characters';
+
+to get Perl to work well with them.  The catch is that you
+have to translate from the locale character set to/from Unicode
+yourself.  See L</Unicode IE<sol>O> above for how to
+
+    use open ':locale';
+
+to accomplish this, but full details are in L<perllocale/Unicode and
+UTF-8>, including gotchas that happen if you don't specify
+C<:not_characters>.
 
 =back
 
@@ -751,7 +869,7 @@ The Unicode standard prefers using hexadecimal notation because
 that more clearly shows the division of Unicode into blocks of 256 characters.
 Hexadecimal is also simply shorter than decimal.  You can use decimal
 notation, too, but learning to use hexadecimal just makes life easier
-with the Unicode standard.  The "C<U+HHHH>" notation uses hexadecimal,
+with the Unicode standard.  The C<U+HHHH> notation uses hexadecimal,
 for example.
 
 The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
@@ -783,63 +901,55 @@ show a decimal number in hexadecimal.  If you have just the
 
 Unicode Consortium
 
-    http://www.unicode.org/
+L<http://www.unicode.org/>
 
 =item *
 
 Unicode FAQ
 
-    http://www.unicode.org/unicode/faq/
+L<http://www.unicode.org/unicode/faq/>
 
 =item *
 
 Unicode Glossary
 
-    http://www.unicode.org/glossary/
+L<http://www.unicode.org/glossary/>
+
+=item *
+
+Unicode Recommended Reading List
+
+The Unicode Consortium has a list of articles and books, some of which
+give a much more in depth treatment of Unicode:
+L<http://unicode.org/resources/readinglist.html>
 
 =item *
 
 Unicode Useful Resources
 
-    http://www.unicode.org/unicode/onlinedat/resources.html
+L<http://www.unicode.org/unicode/onlinedat/resources.html>
 
 =item *
 
 Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
 
-    http://www.alanwood.net/unicode/
+L<http://www.alanwood.net/unicode/>
 
 =item *
 
 UTF-8 and Unicode FAQ for Unix/Linux
 
-    http://www.cl.cam.ac.uk/~mgk25/unicode.html
+L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
 
 =item *
 
 Legacy Character Sets
 
-    http://www.czyborra.com/
-    http://www.eki.ee/letter/
+L<http://www.czyborra.com/>
+L<http://www.eki.ee/letter/>
 
 =item *
 
-The Unicode support files live within the Perl installation in the
-directory
-
-    $Config{installprivlib}/unicore
-
-in Perl 5.8.0 or newer, and 
-
-    $Config{installprivlib}/unicode
-
-in the Perl 5.6 series.  (The renaming to F<lib/unicore> was done to
-avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
-The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
-Perl 5.6.1.)  You can find the C<$Config{installprivlib}> by
-
-    perl "-V:installprivlib"
-
 You can explore various information from the Unicode data files using
 the C<Unicode::UCD> module.
 
@@ -854,7 +964,7 @@ If you have the GNU recode installed, you can also use the
 Perl front-end C<Convert::Recode> for character conversions.
 
 The following are fast conversions from ISO 8859-1 (Latin-1) bytes
-to UTF-8 bytes, the code works even with older Perl 5 versions.
+to UTF-8 bytes and back, the code works even with older Perl 5 versions.
 
     # ISO 8859-1 to UTF-8
     s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
@@ -864,8 +974,9 @@ to UTF-8 bytes, the code works even with older Perl 5 versions.
 
 =head1 SEE ALSO
 
-L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
+L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
+L<Unicode::UCD>
 
 =head1 ACKNOWLEDGMENTS
 
@@ -875,6 +986,7 @@ mailing lists for their valuable feedback.
 
 =head1 AUTHOR, COPYRIGHT, AND LICENSE
 
-Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
+Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>.
+Now maintained by Perl 5 Porters.
 
 This document may be distributed under the same terms as Perl itself.