HINT_UTF8 is not propagated to the op tree anymore; add a

perlunicode.pod that reflects changes to unicode support so far

p4raw-id: //depot/perl@4941

2 files changed, 209 insertions, 2 deletions

diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index cba167f652..2b5e4e7233 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -378,8 +378,9 @@ building and installing from source, the defaults should be fine.
 =head2 Unicode and UTF-8 support
 
 Perl can optionally use UTF-8 as its internal representation for character
-strings.  The C<utf8> pragma enables this support in the current lexical
-scope.  See L<utf8> for more information.
+strings.  The C<utf8> and C<byte> pragmas are used to control this support
+in the current lexical scope.  See L<perlunicode>, L<utf8> and L<byte> for
+more information.
 
 =head2 Interpreter cloning, threads, and concurrency
 
@@ -1653,6 +1654,10 @@ A tutorial that introduces the essentials of references.
 
 A tutorial on managing class data for object modules.
 
+=item perlunicode.pod
+
+An introduction to Unicode support features in Perl.
+
 =back
 
 =head1 New or Changed Diagnostics
diff --git a/pod/perlunicode.pod b/pod/perlunicode.pod
new file mode 100644
index 0000000000..b0efcca8df
--- /dev/null
+++ b/pod/perlunicode.pod
@@ -0,0 +1,202 @@
+=head1 NAME
+
+perlunicode - Unicode support in Perl
+
+=head1 DESCRIPTION
+
+WARNING: The implementation of Unicode support in Perl is incomplete.
+Expect sudden and unannounced changes!
+
+Beginning with version 5.6, Perl uses logically wide characters to
+represent strings internally.  This internal representation of strings
+uses the UTF-8 encoding.
+
+In future, Perl-level operations will expect to work with characters
+rather than bytes, in general.
+
+However, Perl v5.6 aims to provide a safe migration path from byte
+semantics to character semantics for programs.  To preserve compatibility
+with earlier versions of Perl which allowed byte semantics in Perl
+operations (owing to the fact that the internal representation for
+characters was in bytes) byte semantics will continue to be in effect
+until a the C<utf8> pragma is used in the C<main> package, or the C<$^U>
+global flag is explicitly set.
+
+Under character semantics, many operations that formerly operated on
+bytes change to operating on characters.  For ASCII data this makes
+no difference, because UTF-8 stores ASCII in single bytes, but for
+any character greater than C<chr(127)>, the character is stored in
+a sequence of two or more bytes, all of which have the high bit set.
+But by and large, the user need not worry about this, because Perl
+hides it from the user.  A character in Perl is logically just a number
+ranging from 0 to 2**32 or so.  Larger characters encode to longer
+sequences of bytes internally, but again, this is just an internal
+detail which is hidden at the Perl level.
+
+The C<byte> pragma can be used to force byte semantics in a particular
+lexical scope.  See L<byte>.
+
+The C<utf8> pragma is a compatibility device to enables recognition
+of UTF-8 in literals encountered by the parser.  It is also used
+for enabling some experimental Unicode support features.  Note that
+this pragma is only required until a future version of Perl in which
+character semantics will become the default.  This pragma may then
+become a no-op.  See L<utf8>.
+
+Character semantics have the following effects:
+
+=over 4
+
+=item *
+
+Strings and patterns may contain characters that have an ordinal value
+larger than 255.  In Perl v5.6, this is only enabled if the lexical
+scope has a C<use utf8> declaration (due to compatibility needs) but
+future versions may enable this by default.
+
+Presuming you use a Unicode editor to edit your program, such characters
+will typically occur directly within the literal strings as UTF-8
+characters, but you can also specify a particular character with an
+extension of the C<\x> notation.  UTF-8 characters are specified by
+putting the hexadecimal code within curlies after the C<\x>.  For instance,
+a Unicode smiley face is C<\x{263A}>.  A character in the Latin-1 range
+(128..255) should be written C<\x{ab}> rather than C<\xab>, since the
+former will turn into a two-byte UTF-8 code, while the latter will
+continue to be interpreted as generating a 8-bit byte rather than a
+character.  In fact, if C<-w> is turned on, it will produce a warning
+that you might be generating invalid UTF-8.
+
+=item *
+
+Identifiers within the Perl script may contain Unicode alphanumeric
+characters, including ideographs.  (You are currently on your own when
+it comes to using the canonical forms of characters--Perl doesn't (yet)
+attempt to canonicalize variable names for you.)
+
+This also needs C<use utf8> currently.  [XXX: Why?  High-bit chars were
+syntax errors when they occurred within identifiers in previous versions,
+so this should be enabled by default.]
+
+=item *
+
+Regular expressions match characters instead of bytes.  For instance,
+"." matches a character instead of a byte.  (However, the C<\C> pattern
+is provided to force a match a single byte ("C<char>" in C, hence
+C<\C>).)
+
+Unicode support in regular expressions needs C<use utf8> currently.
+[XXX: Because the SWASH routines need to be loaded.  And the RE engine
+appears to need an overhaul to Unicode by default anyway.]
+
+=item *
+
+Character classes in regular expressions match characters instead of
+bytes, and match against the character properties specified in the
+Unicode properties database.  So C<\w> can be used to match an ideograph,
+for instance.
+
+C<use utf8> is needed to enable this.  See above.
+
+=item *
+
+Named Unicode properties and block ranges make be used as character
+classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
+match property) constructs.  For instance, C<\p{Lu}> matches any
+character with the Unicode uppercase property, while C<\p{M}> matches
+any mark character.  Single letter properties may omit the brackets, so
+that can be written C<\pM> also.  Many predefined character classes are
+available, such as C<\p{IsMirrored}> and  C<\p{InTibetan}>.
+
+C<use utf8> is needed to enable this.  See above.
+
+=item *
+
+The special pattern C<\X> match matches any extended Unicode sequence
+(a "combining character sequence" in Standardese), where the first
+character is a base character and subsequent characters are mark
+characters that apply to the base character.  It is equivalent to
+C<(?:\PM\pM*)>.
+
+C<use utf8> is needed to enable this.  See above.
+
+=item *
+
+The C<tr///> operator translates characters instead of bytes.  It can also
+be forced to translate between 8-bit codes and UTF-8 regardless of the
+surrounding utf8 state.  For instance, if you know your input in Latin-1,
+you can say:
+
+    use utf8;
+    while (<>) {
+	tr/\0-\xff//CU;		# latin1 char to utf8
+	...
+    }
+
+Similarly you could translate your output with
+
+    tr/\0-\x{ff}//UC;		# utf8 to latin1 char
+
+No, C<s///> doesn't take /U or /C (yet?).
+
+C<use utf8> is needed to enable this.  See above.
+
+=item *
+
+Case translation operators use the Unicode case translation tables
+when provided character input.  Note that C<uc()> translates to
+uppercase, while C<ucfirst> translates to titlecase (for languages
+that make the distinction).  Naturally the corresponding backslash
+sequences have the same semantics.
+
+=item *
+
+Most operators that deal with positions or lengths in the string will
+automatically switch to using character positions, including C<chop()>,
+C<substr()>, C<pos()>, C<index()>, C<rindex()>, C<sprintf()>,
+C<write()>, and C<length()>.  Operators that specifically don't switch
+include C<vec()>, C<pack()>, and C<unpack()>.  Operators that really
+don't care include C<chomp()>, as well as any other operator that
+treats a string as a bucket of bits, such as C<sort()>, and the
+operators dealing with filenames.
+
+=item *
+
+The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
+since they're often used for byte-oriented formats.  (Again, think
+"C<char>" in the C language.)  However, there is a new "C<U>" specifier
+that will convert between UTF-8 characters and integers.  (It works
+outside of the utf8 pragma too.)
+
+=item *
+
+The C<chr()> and C<ord()> functions work on characters.  This is like
+C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and
+C<unpack("C")>.  In fact, the latter are how you now emulate
+byte-oriented C<chr()> and C<ord()> under utf8.
+
+=item *
+
+And finally, C<scalar reverse()> reverses by character rather than by byte.
+
+=back
+
+=head1 CAVEATS
+
+As of yet, there is no method for automatically coercing input and
+output to some encoding other than UTF-8.  This is planned in the near
+future, however.
+
+Whether a piece of data will be treated as "characters" or "bytes"
+by internal operations cannot be divined at the current time.
+
+Use of locales with utf8 may lead to odd results.  Currently there is
+some attempt to apply 8-bit locale info to characters in the range
+0..255, but this is demonstrably incorrect for locales that use
+characters above that range (when mapped into Unicode).  It will also
+tend to run slower.  Avoidance of locales is strongly encouraged.
+
+=head1 SEE ALSO
+
+L<byte>, L<utf8>, L<perlvar/"$^U">
+
+=cut