X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/58c274a11b245c0b622f3aa697372d5c1dc88354..ad4795e78e923065898354b946437030aaeca163:/pod/perluniintro.pod

diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod
index 67ce214..778c5de 100644
--- a/pod/perluniintro.pod
+++ b/pod/perluniintro.pod
@@ -5,160 +5,251 @@ 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 with plans to cover all of the
+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 the characters in almost all modern character set standards,
-covering more than 30 writing systems and hundreds of languages,
-including all commercially important modern languages.  All characters
+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, and especially not to the C language C<char>.
-Unicode is language neutral and display neutral: it doesn't encode the
-language of the text, and it doesn't define fonts or other graphical
+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 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 then unique numbers for those, hexadecimal
-0x0041 or 0x03B1 for those particular characters.  Such unique
-numbers are called I<code points>.
+SMALL LETTER ALPHA> and unique numbers for the characters, in this
+case 0x0041 and 0x03B1, respectively.  These unique numbers are called
+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.  (In case this notation, numbers like 0x0041, is 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>,
-which gives 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":
+"uppercase" or "lowercase", "decimal digit", or "punctuation";
 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 base character and modifiers is called a I<combining character
-sequence>.
-
-Whether to call these combining character sequences, as a whole,            
-"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, one "character", but from the user viewpoint, the sequence as a
-whole is probably considered one "character", since that's probably what   
-it looks like in the context of the user's language.
-
-With this "as a whole" view of characters, the 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, and so we take
-that point of view in this document: one "character" is one Unicode
-code point, be it a base character or a combining character.
-
-For some of the combinations there are I<precomposed> characters,
-for example C<LATIN CAPITAL LETTER A WITH ACUTE> is defined as
-a single code point.  These precomposed characters are, however,
-often available only for some combinations, and mainly they are
-meant to support round-trip conversions between Unicode and legacy
-standards (like the ISO 8859), and in general case the composing
-method is more extensible.  To support conversion between the
-different compositions of the characters, various I<normalization
-forms> are also defined.
+lowercasing, and collating (sorting) are defined.
+
+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>.  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, to 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" breaks down a bit: "at least one number
-for every character" is closer to truth.  (This happens when the same
-character has been encoded in several legacy encodings.)  The converse
-is also not true: not every code point has 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,
-0x10000 (or 65536) characters from 0x0000 to 0xFFFF.  B<This is untrue.>
-Since Unicode 2.0 Unicode has been defined all the way up to 21 bits
-(0x10FFFF), and since 3.1 characters have been defined beyond 0xFFFF.
-The first 0x10000 characters are called the I<Plane 0>, or the I<Basic
-Multilingual Plane> (BMP).  With the 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: a block per language.  B<Also this is untrue.>
-The division into the 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 may
-be more useful: there is C<Latin> script, C<Greek> script, and so on.
-Scripts usually span several parts of several blocks.  For further
-information see L<Unicode::UCD>.
+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 not also 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.
+
+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 65536) characters from C<0x0000> to C<0xFFFF> would be
+needed.  This soon proved to be false, 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 relase 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 principal, 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 are UTF-16 and UTF-32 and their
-big and little endian variants (UTF-8 is byteorder independent).
-The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms.
-
-For more information about encodings, for example to learn what
-I<surrogates> and I<byte order marks> (BOMs) are, see L<perlunicode>.
+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 perhaps the most popular.  UTF-8 is a
+variable length encoding that encodes Unicode characters as 1 to 6
+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 capability of handling
-Unicode natively.  The first recommended release for serious Unicode
-work is Perl 5.8.0, however.  The maintenance release 5.6.1 fixed many
-of the problems of the initial implementation of Unicode, but for
-example regular expressions didn't 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
+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
+serious Unicode work.  The maintenance release 5.6.1 fixed many of the
+problems of the initial Unicode implementation, but for example
+regular expressions still do not work with Unicode in 5.6.1.
+Perl 5.14.0 is the first release where Unicode support is
+(almost) seamlessly integrable without some gotchas (the exception being
+some differences in L<quotemeta|perlfunc/quotemeta>).   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 5.8.0, 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, not attached to the operations.  (There
-is one remaining case where an explicit C<use utf8> is needed: if your
-Perl script is in UTF-8, you can use UTF-8 in your variable and
-subroutine names, and in your string and regular expression literals,
-by saying C<use utf8>.  This is not the default because that would
-break existing scripts having legacy 8-bit data in them.)
+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.
+Starting with Perl 5.8.0, 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.  See L<utf8>.
 
 =head2 Perl's Unicode Model
 
-Perl supports both the old, pre-5.6, model of 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 as Unicodeness cannot be avoided, the data is
-transparently upgraded to Unicode.
+Perl supports both pre-5.6 strings of eight-bit native bytes, and
+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.  Prior to Perl 5.14, 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
+UTF-8, to encode Unicode strings. Specifically, if all code points in
+the string are C<0xFF> or less, Perl uses the native eight-bit
+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 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"'
+
+produces a fairly useless mixture of native bytes and UTF-8, as well
+as a warning:
+
+     Wide character in print at ...
+
+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 removes the program's warning.
 
-The internal encoding of Unicode in Perl is UTF-8.  The internal
-encoding is normally hidden, however, and one need not and should not
-worry about the internal encoding at all: it is all just characters.
+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.
 
-Perl 5.8.0 will also support Unicode on EBCDIC platforms.  There the
-support is somewhat harder to implement since additional conversions
-are needed at every step.  Because of these difficulties the Unicode
-support won't be quite as full as in other, mainly ASCII-based,
-platforms (the Unicode support will be better than in the 5.6 series,
-which didn't work much at all for EBCDIC platform).  On EBCDIC
-platforms the internal encoding form used is UTF-EBCDIC.
+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.
+
+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.
+
+Later Perl releases have added code that will not work on EBCDIC platforms, and
+no one has complained, so the divergence has continued.  If you want to run
+Perl on an EBCDIC platform, send email to perlbug@perl.org
+
+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".
 
 =head2 Creating Unicode
 
-To create Unicode literals, use the C<\x{...}> notation in
-doublequoted strings:
+To create Unicode characters in literals for code points above C<0xFF>,
+use the C<\x{...}> notation in double-quoted strings:
 
     my $smiley = "\x{263a}";
 
-Similarly for regular expression literals
+Similarly, it can be used in regular expression literals
 
     $smiley =~ /\x{263a}/;
 
@@ -166,19 +257,21 @@ At run-time you can use C<chr()>:
 
     my $hebrew_alef = chr(0x05d0);
 
-(See L</"Further Resources"> for how to find all these numeric codes.)
+See L</"Further Resources"> for how to find all these numeric codes.
 
-Naturally, C<ord()> will do the reverse: turn a character to a code point.
+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 0x100 (decimal 256) will
+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 0x100 or more, Unicode will always be
-produced.  If you want UTF-8 always, use C<pack("U", ...)> instead of
-C<\x..>, C<\x{...}>, or C<chr()>.
+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()>.
 
 You can also use the C<charnames> pragma to invoke characters
-by name in doublequoted strings:
+by name in double-quoted strings:
 
     use charnames ':full';
     my $arabic_alef = "\N{ARABIC LETTER ALEF}";
@@ -190,7 +283,16 @@ characters:
 
 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()>.
+run-time functionality, use C<chr()> and C<charnames::string_vianame()>.
+
+If you want to force the result to Unicode characters, use the special
+C<"U0"> prefix.  It consumes no arguments but causes the following bytes
+to be interpreted as the UTF-8 encoding of Unicode characters:
+
+   my $chars = pack("U0W*", 0x80, 0x42);
+
+Likewise, you can stop such UTF-8 interpretation by using the special
+C<"C0"> prefix.
 
 =head2 Handling Unicode
 
@@ -199,72 +301,89 @@ 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 does B<not> consider combining character sequences
-to be characters, such 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";
 
 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.)
 
-When life is not quite so transparent is working with legacy
-encodings, and I/O, and certain special cases.
+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
+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).
 
-in which case literals (string or regular expression) and chr/ord
-in your whole script are assumed to produce Unicode characters from
-ISO 8859-2 code points.  Note that the matching for the encoding 
-names is forgiving: instead of C<latin2> you could have said 
-C<Latin 2>, or C<iso8859-2>, and so forth.  With just
-
-    use encoding;
-
-first the environment variable C<PERL_ENCODING> will be consulted,
-and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed.
-
-The C<Encode> module knows about many encodings and it has interfaces
+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
 
-Normally writing out Unicode data
+Normally, writing out Unicode data
 
-    print FH chr(0x100), "\n";
+    print FH $some_string_with_unicode, "\n";
 
-will print out the raw UTF-8 bytes, but you will get a warning
-out of that if you use C<-w> or C<use warnings>.  To avoid the
-warning open the stream explicitly in UTF-8:
+produces raw bytes that Perl happens to use to internally encode the
+Unicode string.  Perl's internal encoding depends on the system as
+well as what characters happen to be in the string at the time. If
+any of the characters are at code points C<0x100> or above, you will get
+a warning.  To ensure that the output is explicitly rendered in the
+encoding you desire--and to avoid the warning--open the stream with
+the desired encoding. Some examples:
 
     open FH, ">:utf8", "file";
 
-and on already open streams use C<binmode()>:
+    open FH, ">:encoding(ucs2)",      "file";
+    open FH, ">:encoding(UTF-8)",     "file";
+    open FH, ">:encoding(shift_jis)", "file";
+
+and on already open streams, use C<binmode()>:
 
     binmode(STDOUT, ":utf8");
 
-Reading in correctly formed UTF-8 data will not magically turn
-the data into Unicode in Perl's eyes.
+    binmode(STDOUT, ":encoding(ucs2)");
+    binmode(STDOUT, ":encoding(UTF-8)");
+    binmode(STDOUT, ":encoding(shift_jis)");
 
-You can use either the C<':utf8'> I/O discipline when opening files
+The matching of encoding names is loose: case does not matter, and
+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).
 
-    open(my $fh,'<:utf8', 'anything');
-    my $line_of_utf8 = <$fh>;
+See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
+L<Encode::PerlIO> for the C<:encoding()> layer, and
+L<Encode::Supported> for many encodings supported by the C<Encode>
+module.
 
-The I/O disciplines can also be specified more flexibly with
-the C<open> pragma; see L<open>:
+Reading in a file that you know happens to be encoded in one of the
+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
 
-    use open ':utf8'; # input and output default discipline will be UTF-8
+    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 layers can also be specified more flexibly with
+the C<open> pragma.  See L<open>, or look at the following example.
+
+    use open ':encoding(utf8)'; # input/output default encoding will be
+                                # UTF-8
     open X, ">file";
     print X chr(0x100), "\n";
     close X;
@@ -272,10 +391,11 @@ the C<open> pragma; see L<open>:
     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
@@ -284,97 +404,93 @@ 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 $line_of_iliad = <$epic>;
-
-Both of these methods install a transparent filter on the I/O stream that
-will convert data from the specified encoding when it is read in from the
-stream.  In the first example the F<anything> file is assumed to be UTF-8
-encoded Unicode, in the second example the F<iliad.greek> file is assumed
-to be ISO-8858-7 encoded Greek, but the lines read in will be in both
-cases Unicode.
+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>.
+C<binmode()>; see L<perlfunc/binmode>.
 
 The C<:locale> does not currently (as of Perl 5.8.0) work with
 C<open()> and C<binmode()>, only with the C<open> pragma.  The
-C<:utf8> and C<:encoding(...)> do work with all of C<open()>,
+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 input streams to
-automatically convert data from the specified encoding when it is
-written to the stream.
+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 $unicode, '<:utf8',                 'japanese.uni');
-    open(my $nihongo, '>:encoding(iso2022-jp)', 'japanese.jp');
-    while (<$unicode>) { print $nihongo }
+    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 similarly understanding as with the C<encoding> pragma:
-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>.
+standardisation organisations are recognised; for a more detailed
+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 "input is not UTF-8"
+Notice that because of the default behaviour of not doing any
+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 it in UTF-8:
+by repeatedly encoding the data:
 
     # BAD CODE WARNING
     open F, "file";
-    local $/; # read in the whole file
+    local $/; ## read in the whole file of 8-bit characters
     $t = <F>;
     close F;
-    open F, ">:utf8", "file";
-    print F $t;
+    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 the new PerlIO feature (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 will convert
+simple ASCII (or EBCDIC) text.  The following subroutine converts
 its argument so that Unicode characters with code points greater than
-255 are displayed as "\x{...}", control characters (like "\n") are
-displayed as "\x..", and the rest of the characters as themselves.
-
-   sub nice_string {
-       join("",
-         map { $_ > 255 ?                  # if wide character...
-               sprintf("\\x{%x}", $_) :    # \x{...}
-               chr($_) =~ /[[: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")
 
-will return:
+returns the string
 
-   "foo\x{100}bar\x0a"
+   'foo\x{0100}bar\x0A'
+
+which is ready to be printed.
 
 =head2 Special Cases
 
@@ -384,31 +500,39 @@ will return:
 
 Bit Complement Operator ~ And vec()
 
-The bit complement operator C<~> will produce surprising results if
-used on strings containing Unicode characters.  The results are
-consistent with the internal UTF-8 encoding of the characters, but not
-with much else.  So don't do that.  Similarly for vec(): you will be
-operating on the UTF-8 bit patterns of the Unicode characters, not on
-the bytes, 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 *
 
-Peeking At UTF-8
+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 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 will print c4 80 for the UTF-8 bytes 0xc4 0x80
-    print join(" ", unpack("H*", pack("U", 0x100))), "\n";
+    # this prints  c4 80  for the UTF-8 bytes 0xc4 0x80
+    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 will show the UTF8 flag in FLAGS and both the UTF-8 bytes
-and Unicode characters in PV.  See also later in this document
-the discussion about the C<is_utf8> function of the C<Encode> module.
+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<utf8::is_utf8()> function.
 
 =back
 
@@ -421,32 +545,30 @@ the discussion about the C<is_utf8> function of the C<Encode> module.
 String Equivalence
 
 The question of string equivalence turns somewhat complicated
-in Unicode: what do you mean by equal?
+in Unicode: what do you mean by "equal"?
 
 (Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
 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 being considered equal, or even any As of any case,
-would be desirable.
+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 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>, and Unicode Technical
-Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
-Mappings>, http://www.unicode.org/unicode/reports/tr15/
-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.
 
 =item *
 
 String Collation
 
-People like to see their strings nicely sorted, or as Unicode
+People like to see their strings nicely sorted--or as Unicode
 parlance goes, collated.  But again, what do you mean by collate?
 
 (Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
@@ -454,12 +576,13 @@ 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 0x00C1 > 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
 
@@ -469,28 +592,32 @@ http://www.unicode.org/unicode/reports/tr10/
 
 =item *
 
-Character Ranges
+Character Ranges and Classes
+
+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}>).
 
-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]]/> for that).
+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>.
 
-For specifying things 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
-that means that particular code point range, nothing more.  For
-further information, see L<perlunicode>.
+You can use Unicode code points as the end points of character ranges, and the
+range will include all Unicode code points that lie between those end points.
 
 =item *
 
 String-To-Number Conversions
 
-Unicode does define several other decimal (and numeric) characters
-than just the familiar 0 to 9, such as the Arabic and Indic digits.
+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).
+To get safe conversions from any Unicode string, use
+L<Unicode::UCD/num()>.
 
 =back
 
@@ -498,134 +625,212 @@ than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
 
 =over 4
 
-=item Will My Old Scripts Break?
+=item *
+
+Will My Old Scripts Break?
 
 Very probably not.  Unless you are generating Unicode characters
-somehow, any 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 (for example, C<chr(300)>
-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 How Do I Make My Scripts Work With Unicode?
+=item *
+
+How Do I Make My Scripts Work With Unicode?
 
 Very little work should be needed since nothing changes until you
-somehow generate Unicode data.  The greatest trick will be getting
-input as Unicode, and 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?
+How Do I Know Whether My String Is In Unicode?
 
-You shouldn't care.  No, you really shouldn't.  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 semantics of 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
 code points greater than 0xFF (255) or even 0x80 (128), or that the
 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
-$string.  If the flag is on, characters added to that string will be
-automatically upgraded to UTF-8 (and even then only if they really
-need to be upgraded, that is, if their code point is greater than 0xFF).
+C<$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 (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,
+
+    $a = "ab\x80c";
+    $b = "\x{100}";
+    print "$a = $b\n";
+
+the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
+C<$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 the C<bytes> pragma
-and its only defined function C<length()>:
+instead of the character length. For that use either the
+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($unicode)), "\n"; # will print 2
     use bytes;
-    print length($unicode), "\n"; # will 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 How Do I Detect Invalid UTF-8?
+=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 *
 
-Either
+How Do I Detect Data That's Not Valid In a Particular Encoding?
 
-    use Encode 'encode_utf8';
-    if (encode_utf8($string)) {
-        # valid
+Use the C<Encode> package to try converting it.
+For example,
+
+    use Encode 'decode_utf8';
+
+    if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
+        # $string is valid utf8
     } else {
-        # invalid
+        # $string is not valid utf8
     }
 
-or
+Or use C<unpack> to try decoding it:
 
     use warnings;
-    @chars = unpack("U0U*", "\xFF"); # will warn
+    @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
 
-The warning will be C<Malformed UTF-8 character (byte 0xff) in
-unpack>.  The "U0" means "expect strictly UTF-8 encoded Unicode".
-Without that the C<unpack("U*", ...)> would accept also data like
-C<chr(0xFF>).
+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 How Do I Convert Data Into UTF-8?  Or Vice Versa?
+=item *
 
-This probably isn't as useful (or simple) as you might think.
-Also, normally you shouldn't need to.
+How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
 
-In one sense what you are asking doesn't make much sense: UTF-8 is
-(intended as an) Unicode encoding, so converting "data" into UTF-8
-isn't meaningful unless you know in what character set and encoding
-the binary data is in, and in this case you can use C<Encode>.
+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
+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>:
 
     use Encode 'from_to';
     from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
 
-If you have ASCII (really 7-bit US-ASCII), you already have valid
-UTF-8, the lowest 128 characters of UTF-8 encoded Unicode and US-ASCII
-are equivalent.
+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:
 
-If you have Latin-1 (or want Latin-1), you can just use pack/unpack:
+   use Translate;
+   my $phrase = "Yes";
+   Translate::from_to($phrase, 'english', 'deutsch');
+   ## phrase now contains "Ja"
 
-    $latin1 = pack("C*", unpack("U*", $utf8));
-    $utf8   = pack("U*", unpack("C*", $latin1));
+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.
 
-(The same works for EBCDIC.)
+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("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:
 
     use Encode 'decode_utf8';
-    $utf8 = decode_utf8($bytes);
+    $Unicode = decode_utf8($bytes);
+
+or:
 
-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/UTF-8 data by C<pack("U*", 0xff, ...)>.
+    $Unicode = pack("U0a*", $bytes);
 
-=item How Do I Display Unicode?  How Do I Input Unicode?
+You can find the bytes that make up a UTF-8 sequence with
 
-See http://www.hclrss.demon.co.uk/unicode/ and
-http://www.cl.cam.ac.uk/~mgk25/unicode.html
+    @bytes = unpack("C*", $Unicode_string)
+
+and you can create well-formed Unicode with
+
+    $Unicode_string = pack("U*", 0xff, ...)
+
+=item *
 
-=item How Does Unicode Work With Traditional Locales?
+How Do I Display Unicode?  How Do I Input Unicode?
 
-In Perl, not very well.  Avoid using locales through the C<locale>
-pragma.  Use only one or the other.
+See L<http://www.alanwood.net/unicode/> and
+L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
+
+=item *
+
+How Does Unicode Work With Traditional Locales?
+
+Perl tries to keep the two separated.  Code points that are above 255
+are treated as Unicode; those below 256, generally as locale.  This
+works reasonably well except in some case-insensitive regular expression
+pattern matches that in Unicode would cross the 255/256 boundary.  These
+are disallowed.
+Also, the C<\p{}> and C<\N{}> constructs silently assume Unicode values
+even for code points below 256.
+See also L<perlrun> for the
+description of the C<-C> switch and its environment counterpart,
+C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
+for example by using locale settings.
 
 =back
 
 =head2 Hexadecimal Notation
 
-The Unicode standard prefers using hexadecimal notation because that
-shows better the division of Unicode into blocks of 256 characters.
+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.
+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>
 a-f (or A-F, case doesn't matter).  Each hexadecimal digit represents
 four bits, or half a byte.  C<print 0x..., "\n"> will show a
 hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
 show a decimal number in hexadecimal.  If you have just the
-"hexdigits" of a hexadecimal number, you can use the C<hex()>
-function.
+"hex digits" of a hexadecimal number, you can use the C<hex()> function.
 
     print 0x0009, "\n";    # 9
     print 0x000a, "\n";    # 10
@@ -649,68 +854,55 @@ function.
 
 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.hclrss.demon.co.uk/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 
-
-    $Config{installprivlib}/unicode
-
-in the Perl 5.6 series.  (The renaming to F<lib/unicore> was done to
-avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
-The main Unicode data file is F<Unicode.txt> (or F<Unicode.301> in
-Perl 5.6.1.)  You can find the C<$Config{installprivlib}> by
-
-    perl "-V:installprivlib"
-
-Note that some of the files have been renamed from the Unicode
-standard since the Perl installation tries to live by the "8.3"
-filenaming restrictions.  The renamings are shown in the
-accompanying F<rename> file.
-
 You can explore various information from the Unicode data files using
 the C<Unicode::UCD> module.
 
@@ -722,14 +914,24 @@ If you cannot upgrade your Perl to 5.8.0 or later, you can still
 do some Unicode processing by using the modules C<Unicode::String>,
 C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
 If you have the GNU recode installed, you can also use the
-Perl frontend C<Convert::Recode> for character conversions.
+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 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;
+
+    # UTF-8 to ISO 8859-1
+    s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
 
 =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 ACKNOWLEDGEMENTS
+=head1 ACKNOWLEDGMENTS
 
 Thanks to the kind readers of the perl5-porters@perl.org,
 perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
@@ -737,6 +939,6 @@ mailing lists for their valuable feedback.
 
 =head1 AUTHOR, COPYRIGHT, AND LICENSE
 
-Copyright 2001 Jarkko Hietaniemi <jhi@iki.fi>
+Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
 
 This document may be distributed under the same terms as Perl itself.