WARNING: While the implementation of Unicode support in Perl is now fairly
complete it is still evolving to some extent.
-In particular the way Unicode is handled on EBCDIC platforms is still rather
-experimental. On such a platform references to UTF-8 encoding in this
-document and elsewhere should be read as meaning UTF-EBCDIC as specified
-in Unicode Technical Report 16 unless ASCII vs EBCDIC issues are specifically
-discussed. There is no C<utfebcdic> pragma or ":utfebcdic" layer, rather
-"utf8" and ":utf8" are re-used to mean platform's "natural" 8-bit encoding
-of Unicode. See L<perlebcdic> for more discussion of the issues.
+In particular the way Unicode is handled on EBCDIC platforms is still
+rather experimental. On such a platform references to UTF-8 encoding
+in this document and elsewhere should be read as meaning UTF-EBCDIC as
+specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
+are specifically discussed. There is no C<utfebcdic> pragma or
+":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean
+platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for
+more discussion of the issues.
The following areas are still under development.
=item Input and Output Disciplines
-A filehandle can be marked as containing perl's internal Unicode encoding
-(UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
+A filehandle can be marked as containing perl's internal Unicode
+encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
Other encodings can be converted to perl's encoding on input, or from
-perl's encoding on output by use of the ":encoding()" layer.
-There is not yet a clean way to mark the perl source itself as being
-in an particular encoding.
+perl's encoding on output by use of the ":encoding()" layer. There is
+not yet a clean way to mark the Perl source itself as being in an
+particular encoding.
=item Regular Expressions
The regular expression compiler does now attempt to produce
polymorphic opcodes. That is the pattern should now adapt to the data
-and automatically switch to the Unicode character scheme when presented
-with Unicode data, or a traditional byte scheme when presented with
-byte data. The implementation is still new and (particularly on
-EBCDIC platforms) may need further work.
+and automatically switch to the Unicode character scheme when
+presented with Unicode data, or a traditional byte scheme when
+presented with byte data. The implementation is still new and
+(particularly on EBCDIC platforms) may need further work.
=item C<use utf8> still needed to enable a few features
-The C<utf8> pragma implements the tables used for Unicode support. These
-tables are automatically loaded on demand, so the C<utf8> pragma need not
-normally be used.
+The C<utf8> pragma implements the tables used for Unicode support.
+These tables are automatically loaded on demand, so the C<utf8> pragma
+need not normally be used.
-However, as a compatibility measure, this pragma must be explicitly used
-to enable recognition of UTF-8 encoded literals and identifiers in the
-source text on ASCII based machines or recognize UTF-EBCDIC encoded literals
-and identifiers on EBCDIC based machines.
+However, as a compatibility measure, this pragma must be explicitly
+used to enable recognition of UTF-8 encoded literals and identifiers
+in the source text on ASCII based machines or recognize UTF-EBCDIC
+encoded literals and identifiers on EBCDIC based machines.
=back
represent strings internally. This internal representation of strings
uses either the UTF-8 or the UTF-EBCDIC encoding.
-In future, Perl-level operations can be expected to work with characters
-rather than bytes, in general.
+In future, Perl-level operations can be expected to work with
+characters rather than bytes, in general.
-However, as strictly an interim compatibility measure, Perl v5.6 aims to
-provide a safe migration path from byte semantics to character semantics
-for programs. For operations where Perl can unambiguously decide that the
-input data is characters, Perl now switches to character semantics.
-For operations where this determination cannot be made without additional
-information from the user, Perl decides in favor of compatibility, and
-chooses to use byte semantics.
+However, as strictly an interim compatibility measure, Perl aims to
+provide a safe migration path from byte semantics to character
+semantics for programs. For operations where Perl can unambiguously
+decide that the input data is characters, Perl now switches to
+character semantics. For operations where this determination cannot
+be made without additional information from the user, Perl decides in
+favor of compatibility, and chooses to use byte semantics.
This behavior preserves compatibility with earlier versions of Perl,
which allowed byte semantics in Perl operations, but only as long as
external programs, from information provided by the system (such as %ENV),
or from literals and constants in the source text.
-If the C<-C> command line switch is used, (or the ${^WIDE_SYSTEM_CALLS}
-global flag is set to C<1>), all system calls will use the
-corresponding wide character APIs. This is currently only implemented
-on Windows since UNIXes lack API standard on this area.
+If the C<-C> command line switch is used, (or the
+${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
+will use the corresponding wide character APIs. Note that this is
+currently only implemented on Windows since other platforms API
+standard on this area.
-Regardless of the above, the C<bytes> pragma can always be used to force
-byte semantics in a particular lexical scope. See L<bytes>.
+Regardless of the above, the C<bytes> pragma can always be used to
+force byte semantics in a particular lexical scope. See L<bytes>.
The C<utf8> pragma is primarily a compatibility device that enables
-recognition of UTF-(8|EBCDIC) in literals encountered by the parser. It may also
-be used for enabling some of the more 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>.
+recognition of UTF-(8|EBCDIC) in literals encountered by the parser.
+It may also be used for enabling some of the more 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>.
Unless mentioned otherwise, Perl operators will use character semantics
when they are dealing with Unicode data, and byte semantics otherwise.
on Unicode data, the C<bytes> pragma should be used.
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 may be stored in
+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 B<may> be stored in
a sequence of two or more bytes, all of which have the high bit set.
For C1 controls or Latin 1 characters on an EBCDIC platform the
Strings and patterns may contain characters that have an ordinal value
larger than 255.
-Presuming you use a Unicode editor to edit your program, such characters
-will typically occur directly within the literal strings as UTF-(8|EBCDIC)
-characters, but you can also specify a particular character with an
-extension of the C<\x> notation. UTF-X characters are specified by
-putting the hexadecimal code within curlies after the C<\x>. For instance,
-a Unicode smiley face is C<\x{263A}>.
+Presuming you use a Unicode editor to edit your program, such
+characters will typically occur directly within the literal strings as
+UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also
+specify a particular character with an extension of the C<\x>
+notation. UTF-X characters are specified by putting the hexadecimal
+code within curlies after the C<\x>. For instance, a Unicode smiley
+face is C<\x{263A}>.
=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.)
+it comes to using the canonical forms of characters--Perl doesn't
+(yet) attempt to canonicalize variable names for you.)
=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>).)
+is provided to force a match a single byte ("C<char>" in C, hence C<\C>).)
=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.
+Unicode properties database. So C<\w> can be used to match an
+ideograph, for instance.
=item *
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}>. The
-names of the C<In> classes are the official Unicode block names but
-with all non-alphanumeric characters removed, for example the block
-name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>.
+names of the C<In> classes are the official Unicode script and block
+names but with all non-alphanumeric characters removed, for example
+the block name C<"Latin-1 Supplement"> becomes C<\p{InLatin1Supplement}>.
Here is the list as of Unicode 3.1.0 (the two-letter classes) and
as defined by Perl (the one-letter classes) (in Unicode materials
=head2 Scripts
-The scripts available for C<\p{In...}> and C<\P{In...}>, for
-example \p{InCyrillic>, are as follows, for example C<\p{InLatin}>
-or C<\P{InHan}>:
+The scripts available for C<\p{In...}> and C<\P{In...}>, for example
+\p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
Latin
Greek
=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.
+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 bit string operators C<& | ^ ~> can operate on character data.
However, for backward compatibility reasons (bit string operations
-when the characters all are less than 256 in ordinal value) one cannot
-mix C<~> (the bit complement) and characters both less than 256 and
+when the characters all are less than 256 in ordinal value) one should
+not mix C<~> (the bit complement) and characters both less than 256 and
equal or greater than 256. Most importantly, the DeMorgan's laws
(C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold.
Another way to look at this is that the complement cannot return
-B<both> the 8-bit (byte) wide bit complement, and the full character
+B<both> the 8-bit (byte) wide bit complement B<and> the full character
wide bit complement.
=item *
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