summaryrefslogtreecommitdiff
path: root/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
diff options
context:
space:
mode:
Diffstat (limited to 'Master/tlpkg/tlperl/lib/pods/perluniintro.pod')
-rw-r--r--Master/tlpkg/tlperl/lib/pods/perluniintro.pod946
1 files changed, 0 insertions, 946 deletions
diff --git a/Master/tlpkg/tlperl/lib/pods/perluniintro.pod b/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
deleted file mode 100644
index 8ce4b7b4464..00000000000
--- a/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
+++ /dev/null
@@ -1,946 +0,0 @@
-=head1 NAME
-
-perluniintro - Perl Unicode introduction
-
-=head1 DESCRIPTION
-
-This document gives a general idea of Unicode and how to use Unicode
-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 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 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>. 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.
-
-Unicode also defines various I<properties> for the characters, like
-"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 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" 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> 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 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>, which 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 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.
-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 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.
-
-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.
-
-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 characters in literals for code points above C<0xFF>,
-use the C<\x{...}> notation in double-quoted strings:
-
- my $smiley = "\x{263a}";
-
-Similarly, it can be used in regular expression literals
-
- $smiley =~ /\x{263a}/;
-
-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.
-
-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()>.
-
-You can invoke characters
-by name in double-quoted strings:
-
- my $arabic_alef = "\N{ARABIC LETTER ALEF}";
-
-And, as mentioned above, you can also C<pack()> numbers into Unicode
-characters:
-
- my $georgian_an = pack("U", 0x10a0);
-
-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::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
-
-Handling Unicode is for the most part transparent: just use the
-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 grapheme clusters to be separate characters, so for
-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. (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 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 'decode';
- $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
-
-=head2 Unicode I/O
-
-Normally, writing out Unicode data
-
- print FH $some_string_with_unicode, "\n";
-
-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";
-
- 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");
-
- binmode(STDOUT, ":encoding(ucs2)");
- binmode(STDOUT, ":encoding(UTF-8)");
- binmode(STDOUT, ":encoding(shift_jis)");
-
-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).
-
-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.
-
-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
-
- 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;
- open Y, "<file";
- printf "%#x\n", ord(<Y>); # this should print 0x100
- close Y;
-
-With the C<open> pragma you can use the C<:locale> layer
-
- 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
- close O;
- open(I, "<koi8");
- printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
- close I;
-
-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 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
-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 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(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 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::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 layer,
-it is easy to mistakenly write code that keeps on expanding a file
-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, ">: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 ':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 (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", $_) : # \x..
- quotemeta(chr($_)) # else quoted or as themselves
- } unpack("W*", $_[0])); # unpack Unicode characters
- }
-
-For example,
-
- nice_string("foo\x{100}bar\n")
-
-returns the string
-
- 'foo\x{0100}bar\x0A'
-
-which is ready to be printed.
-
-=head2 Special Cases
-
-=over 4
-
-=item *
-
-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.
-
-=item *
-
-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 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("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 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
-
-=head2 Advanced Topics
-
-=over 4
-
-=item *
-
-String Equivalence
-
-The question of string equivalence turns somewhat complicated
-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 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,
-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, 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
-parlance goes, collated. But again, what do you mean by collate?
-
-(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
-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>.
-
-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>
-L<http://www.unicode.org/unicode/reports/tr10/>
-
-=back
-
-=head2 Miscellaneous
-
-=over 4
-
-=item *
-
-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}>).
-
-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>.
-
-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
-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
-
-=head2 Questions With Answers
-
-=over 4
-
-=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)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
-BREVE.
-
-=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 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 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>.)
-
-To determine if a string is in Unicode, use:
-
- 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
-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 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 also print 2
- # (the 0xC4 0x80 of the UTF-8)
- no bytes;
-
-=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 'decode_utf8';
-
- if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
- # $string is valid utf8
- } else {
- # $string is not valid utf8
- }
-
-Or use C<unpack> to try decoding it:
-
- use warnings;
- @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
-
-If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
-"process the string character per character". Without that, the
-C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
-string starts with C<U>) and it would return the bytes making up the UTF-8
-encoding of the target string, something that will always work.
-
-=item *
-
-How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
-
-This probably isn't as useful as you might think.
-Normally, you shouldn't need to.
-
-In one sense, what you are asking doesn't make much sense: encodings
-are for characters, and binary data are not "characters", so converting
-"data" into some encoding isn't meaningful unless you know in what
-character set and encoding the binary data is in, in which case it's
-not just binary data, now is it?
-
-If you have a raw sequence of bytes that you know should be
-interpreted via a particular encoding, you can use C<Encode>:
-
- use Encode 'from_to';
- from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
-
-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:
-
- use Translate;
- my $phrase = "Yes";
- Translate::from_to($phrase, 'english', 'deutsch');
- ## 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.
-
-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';
- $Unicode = decode_utf8($bytes);
-
-or:
-
- $Unicode = pack("U0a*", $bytes);
-
-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 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?
-
-Starting in Perl 5.16, you can specify
-
- use locale ':not_characters';
-
-to get Perl to work well with tradtional locales. 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 specifiy
-C<:not_characters>.
-
-=back
-
-=head2 Hexadecimal Notation
-
-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,
-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
-"hex digits" of a hexadecimal number, you can use the C<hex()> function.
-
- print 0x0009, "\n"; # 9
- print 0x000a, "\n"; # 10
- print 0x000f, "\n"; # 15
- print 0x0010, "\n"; # 16
- print 0x0011, "\n"; # 17
- print 0x0100, "\n"; # 256
-
- print 0x0041, "\n"; # 65
-
- printf "%x\n", 65; # 41
- printf "%#x\n", 65; # 0x41
-
- print hex("41"), "\n"; # 65
-
-=head2 Further Resources
-
-=over 4
-
-=item *
-
-Unicode Consortium
-
-L<http://www.unicode.org/>
-
-=item *
-
-Unicode FAQ
-
-L<http://www.unicode.org/unicode/faq/>
-
-=item *
-
-Unicode 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
-
-L<http://www.unicode.org/unicode/onlinedat/resources.html>
-
-=item *
-
-Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
-
-L<http://www.alanwood.net/unicode/>
-
-=item *
-
-UTF-8 and Unicode FAQ for Unix/Linux
-
-L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
-
-=item *
-
-Legacy Character Sets
-
-L<http://www.czyborra.com/>
-L<http://www.eki.ee/letter/>
-
-=item *
-
-You can explore various information from the Unicode data files using
-the C<Unicode::UCD> module.
-
-=back
-
-=head1 UNICODE IN OLDER PERLS
-
-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 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<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
-
-Thanks to the kind readers of the perl5-porters@perl.org,
-perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
-mailing lists for their valuable feedback.
-
-=head1 AUTHOR, COPYRIGHT, AND LICENSE
-
-Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
-
-This document may be distributed under the same terms as Perl itself.