perluniintro: Update for 5.14

This includes some edits that I believe clarify the original language.

1 files changed, 98 insertions, 54 deletions

diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod
index d3e322a92a..3768b45db1 100644
--- a/pod/perluniintro.pod
+++ b/pod/perluniintro.pod
@@ -5,21 +5,22 @@ 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 4.0 in April 2003.
+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>.
@@ -31,7 +32,9 @@ 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
@@ -51,33 +54,35 @@ 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, and then the
-I<extended grapheme cluster>.  For example, a Korean Hangul syllable is
-considered a single logical character, but most often consists of three actual
+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".  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.
-
-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.
+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" idea breaks down a bit: instead, there is
@@ -128,24 +133,36 @@ 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.
-
-B<Starting from Perl 5.8.0, the use of C<use utf8> is needed only in much more restricted circumstances.> In earlier releases the C<utf8> pragma was used to declare
+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, 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
+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 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
-as Unicodeness cannot be avoided, the data is (mostly) transparently upgraded
-to Unicode.  There are some problems--see L<perlunicode/The "Unicode Bug">.
+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
@@ -182,10 +199,11 @@ 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, too:
+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 complain
-about the malformed UTF-8.
+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:
@@ -273,16 +291,18 @@ example
     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 an extended grapheme cluster.
+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.
+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:
@@ -321,9 +341,12 @@ and on already open streams, use C<binmode()>:
 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 C<:utf8> is unsafe for
+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
-UTF8.
+UTF8; you should instead use C<:encoding(UTF-8)> (unfortunately this
+specification needs to be in all upper-case with the dash to get the
+safety checking; C<:encoding(utf-8)>, for example, doesn't do the
+checking).
 
 See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
 L<Encode::PerlIO> for the C<:encoding()> layer, and
@@ -515,7 +538,7 @@ 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 Report #15,
@@ -577,6 +600,8 @@ 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
 
@@ -603,13 +628,18 @@ How Do I Make My Scripts Work With Unicode?
 Very little work should be needed since nothing changes until you
 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 *
 
 How Do I Know Whether My String Is In Unicode?
 
-You shouldn't have to care.  But you may, because currently the semantics of the
-characters whose ordinals are in the range 128 to 255 are different depending on
+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>.)
 
@@ -627,7 +657,7 @@ 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, and
+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,
 
@@ -640,20 +670,26 @@ 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
-the C<length()> function:
+C<Encode::encode_utf8()> function or the (deprecated) 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($unicode)), "\n"; # will print 2
-    use bytes;
+    use bytes;                    # DEPRECATED!
     print length($unicode), "\n"; # will also print 2
                                   # (the 0xC4 0x80 of the UTF-8)
     no bytes;
 
 =item *
 
+How Do I Find Out What Encoding a File Has?
+
+Try L<Encode::Guess>.
+
+=item *
+
 How Do I Detect Data That's Not Valid In a Particular Encoding?
 
 Use the C<Encode> package to try converting it.
@@ -812,6 +848,14 @@ 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
 
 L<http://www.unicode.org/unicode/onlinedat/resources.html>
@@ -873,6 +917,6 @@ mailing lists for their valuable feedback.
 
 =head1 AUTHOR, COPYRIGHT, AND LICENSE
 
-Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
+Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
 
 This document may be distributed under the same terms as Perl itself.