lib/utf8.pm: pod changes

See thread beginning at
http://nntp.perl.org/group/perl.perl5.porters/233125

1 files changed, 57 insertions, 70 deletions

diff --git a/lib/utf8.pm b/lib/utf8.pm
index 1177841338..324cb87c86 100644
--- a/lib/utf8.pm
+++ b/lib/utf8.pm
@@ -2,7 +2,7 @@ package utf8;
 
 $utf8::hint_bits = 0x00800000;
 
-our $VERSION = '1.18';
+our $VERSION = '1.19';
 
 sub import {
     $^H |= $utf8::hint_bits;
@@ -47,8 +47,9 @@ utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
  $unicode = utf8::native_to_unicode(ord('A')); # returns 65 on both
                                                # ASCII and EBCDIC
                                                # platforms
- $native = utf8::unicode_to_native(65);       # returns 65 on ASCII
-                                              # platforms; 193 on EBCDIC
+ $native = utf8::unicode_to_native(65);        # returns 65 on ASCII
+                                               # platforms; 193 on
+                                               # EBCDIC
 
  $flag = utf8::is_utf8($string); # since Perl 5.8.1
  $flag = utf8::valid($string);
@@ -56,9 +57,11 @@ utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
 =head1 DESCRIPTION
 
 The C<use utf8> pragma tells the Perl parser to allow UTF-8 in the
-program text in the current lexical scope (allow UTF-EBCDIC on EBCDIC based
-platforms).  The C<no utf8> pragma tells Perl to switch back to treating
-the source text as literal bytes in the current lexical scope.
+program text in the current lexical scope.  The C<no utf8> pragma tells Perl
+to switch back to treating the source text as literal bytes in the current
+lexical scope.  (On EBCDIC platforms, technically it is allowing UTF-EBCDIC,
+and not UTF-8, but this distinction is academic, so in this document the term
+UTF-8 is used to mean both).
 
 B<Do not use this pragma for anything else than telling Perl that your
 script is written in UTF-8.> The utility functions described below are
@@ -69,9 +72,7 @@ encodings, you need either a Byte Order Mark at the beginning of your
 source code, or C<use utf8;>, to instruct perl.
 
 When UTF-8 becomes the standard source format, this pragma will
-effectively become a no-op.  For convenience in what follows the term
-I<UTF-X> is used to refer to UTF-8 on ASCII and ISO Latin based
-platforms and UTF-EBCDIC on EBCDIC based platforms.
+effectively become a no-op.
 
 See also the effects of the C<-C> switch and its cousin, the
 C<PERL_UNICODE> environment variable, in L<perlrun>.
@@ -82,22 +83,17 @@ Enabling the C<utf8> pragma has the following effect:
 
 =item *
 
-Bytes in the source text that have their high-bit set will be treated
-as being part of a literal UTF-X sequence.  This includes most
+Bytes in the source text that are not in the ASCII character set will be
+treated as being part of a literal UTF-8 sequence.  This includes most
 literals such as identifier names, string constants, and constant
 regular expression patterns.
 
-On EBCDIC platforms characters in the Latin 1 character set are
-treated as being part of a literal UTF-EBCDIC character.
-
 =back
 
-Note that if you have bytes with the eighth bit on in your script
-(for example embedded Latin-1 in your string literals), C<use utf8>
-will be unhappy since the bytes are most probably not well-formed
-UTF-X.  If you want to have such bytes under C<use utf8>, you can disable
-this pragma until the end the block (or file, if at top level) by
-C<no utf8;>.
+Note that if you have non-ASCII, non-UTF-8 bytes in your script (for example
+embedded Latin-1 in your string literals), C<use utf8> will be unhappy.  If
+you want to have such bytes under C<use utf8>, you can disable this pragma
+until the end the block (or file, if at top level) by C<no utf8;>.
 
 =head2 Utility functions
 
@@ -109,23 +105,24 @@ you should not say that unless you really want to have UTF-8 source code.
 
 =item * C<$num_octets = utf8::upgrade($string)>
 
+(Since Perl v5.8.0)
 Converts in-place the internal representation of the string from an octet
-sequence in the native encoding (Latin-1 or EBCDIC) to I<UTF-X>. The
+sequence in the native encoding (Latin-1 or EBCDIC) to UTF-8. The
 logical character sequence itself is unchanged.  If I<$string> is already
-stored as I<UTF-X>, then this is a no-op. Returns the
-number of octets necessary to represent the string as I<UTF-X>.  Can be
+stored as UTF-8, then this is a no-op. Returns the
+number of octets necessary to represent the string as UTF-8.  Can be
 used to make sure that the UTF-8 flag is on, so that C<\w> or C<lc()>
-work as Unicode on strings containing characters in the range 0x80-0xFF
-(on ASCII and derivatives).
+work as Unicode on strings containing non-ASCII characters whose code points
+are below 256.
 
-B<Note that this function does not handle arbitrary encodings.>
-Therefore Encode is recommended for the general purposes; see also
-L<Encode>.
+B<Note that this function does not handle arbitrary encodings>;
+use L<Encode> instead.
 
 =item * C<$success = utf8::downgrade($string[, $fail_ok])>
 
+(Since Perl v5.8.0)
 Converts in-place the internal representation of the string from
-I<UTF-X> to the equivalent octet sequence in the native encoding (Latin-1
+UTF-8 to the equivalent octet sequence in the native encoding (Latin-1
 or EBCDIC). The logical character sequence itself is unchanged. If
 I<$string> is already stored as native 8 bit, then this is a no-op.  Can
 be used to
@@ -133,56 +130,52 @@ make sure that the UTF-8 flag is off, e.g. when you want to make sure
 that the substr() or length() function works with the usually faster
 byte algorithm.
 
-Fails if the original I<UTF-X> sequence cannot be represented in the
+Fails if the original UTF-8 sequence cannot be represented in the
 native 8 bit encoding. On failure dies or, if the value of I<$fail_ok> is
 true, returns false. 
 
 Returns true on success.
 
-B<Note that this function does not handle arbitrary encodings.>
-Therefore Encode is recommended for the general purposes; see also
-L<Encode>.
+B<Note that this function does not handle arbitrary encodings>;
+use L<Encode> instead.
 
 =item * C<utf8::encode($string)>
 
+(Since Perl v5.8.0)
 Converts in-place the character sequence to the corresponding octet
-sequence in I<UTF-X>. That is, every (possibly wide) character gets
+sequence in UTF-8. That is, every (possibly wide) character gets
 replaced with a sequence of one or more characters that represent the
-individual I<UTF-X> bytes of the character.  The UTF8 flag is turned off.
+individual UTF-8 bytes of the character.  The UTF8 flag is turned off.
 Returns nothing.
 
  my $a = "\x{100}"; # $a contains one character, with ord 0x100
  utf8::encode($a);  # $a contains two characters, with ords (on
-                    # ASCII platforms) 0xc4 and 0x80
+                    # ASCII platforms) 0xc4 and 0x80.  On EBCDIC
+                    # 1047, this would instead be 0x8C and 0x41.
 
-B<Note that this function does not handle arbitrary encodings.>
-Therefore Encode is recommended for the general purposes; see also
-L<Encode>.
+B<Note that this function does not handle arbitrary encodings>;
+use L<Encode> instead.
 
 =item * C<$success = utf8::decode($string)>
 
-Attempts to convert in-place the octet sequence encoded as I<UTF-X> to the
+(Since Perl v5.8.0)
+Attempts to convert in-place the octet sequence encoded as UTF-8 to the
 corresponding character sequence. That is, it replaces each sequence of
-characters in the string whose ords represent a valid UTF-X byte
+characters in the string whose ords represent a valid UTF-8 byte
 sequence, with the corresponding single character.  The UTF-8 flag is
-turned on only if the source string contains multiple-byte I<UTF-X>
-characters.  If I<$string> is invalid as I<UTF-X>, returns false;
+turned on only if the source string contains multiple-byte UTF-8
+characters.  If I<$string> is invalid as UTF-8, returns false;
 otherwise returns true.
 
  my $a = "\xc4\x80"; # $a contains two characters, with ords
                      # 0xc4 and 0x80
  utf8::decode($a);   # On ASCII platforms, $a contains one char,
-                     # with ord 0x100.   On EBCDIC platforms, $a
-                     # is unchanged and the function returns FALSE.
-
-(C<"\xc4\x80"> is not a valid sequence of bytes in any UTF-8-encoded
-character(s) in the EBCDIC code pages that Perl supports, which is why the
-above example returns failure on them.  What does decode into C<\x{100}>
-depends on the platform.  It is C<"\x8C\x41"> in IBM-1047.)
+                     # with ord 0x100.   Since these bytes aren't
+                     # legal UTF-EBCDIC, on EBCDIC platforms, $a is
+                     # unchanged and the function returns FALSE.
 
-B<Note that this function does not handle arbitrary encodings.>
-Therefore Encode is recommended for the general purposes; see also
-L<Encode>.
+B<Note that this function does not handle arbitrary encodings>;
+use L<Encode> instead.
 
 =item * C<$unicode = utf8::native_to_unicode($code_point)>
 
@@ -215,7 +208,7 @@ platforms, so there is no performance hit in using it there.
 =item * C<$flag = utf8::is_utf8($string)>
 
 (Since Perl 5.8.1)  Test whether I<$string> is marked internally as encoded in
-UTF-8.  Functionally the same as Encode::is_utf8().
+UTF-8.  Functionally the same as C<Encode::is_utf8()>.
 
 =item * C<$flag = utf8::valid($string)>
 
@@ -224,32 +217,26 @@ UTF-8.  Will return true if it is well-formed UTF-8 and has the UTF-8 flag
 on B<or> if I<$string> is held as bytes (both these states are 'consistent').
 Main reason for this routine is to allow Perl's test suite to check
 that operations have left strings in a consistent state.  You most
-probably want to use utf8::is_utf8() instead.
+probably want to use C<utf8::is_utf8()> instead.
 
 =back
 
 C<utf8::encode> is like C<utf8::upgrade>, but the UTF8 flag is
-cleared.  See L<perlunicode> for more on the UTF8 flag and the C API
-functions C<sv_utf8_upgrade>, C<sv_utf8_downgrade>, C<sv_utf8_encode>,
-and C<sv_utf8_decode>, which are wrapped by the Perl functions
+cleared.  See L<perlunicode>, and the C API
+functions C<L<sv_utf8_upgrade|perlapi/sv_utf8_upgrade>>,
+C<L<perlapi/sv_utf8_downgrade>>, C<L<perlapi/sv_utf8_encode>>,
+and C<L<perlapi/sv_utf8_decode>>, which are wrapped by the Perl functions
 C<utf8::upgrade>, C<utf8::downgrade>, C<utf8::encode> and
-C<utf8::decode>.  Also, the functions utf8::is_utf8, utf8::valid,
-utf8::encode, utf8::decode, utf8::upgrade, and utf8::downgrade are
+C<utf8::decode>.  Also, the functions C<utf8::is_utf8>, C<utf8::valid>,
+C<utf8::encode>, C<utf8::decode>, C<utf8::upgrade>, and C<utf8::downgrade> are
 actually internal, and thus always available, without a C<require utf8>
 statement.
 
 =head1 BUGS
 
-One can have Unicode in identifier names, but not in package/class or
-subroutine names.  While some limited functionality towards this does
-exist as of Perl 5.8.0, that is more accidental than designed; use of
-Unicode for the said purposes is unsupported.
-
-One reason of this unfinishedness is its (currently) inherent
-unportability: since both package names and subroutine names may need
-to be mapped to file and directory names, the Unicode capability of
-the filesystem becomes important-- and there unfortunately aren't
-portable answers.
+Some filesystems may not support UTF-8 file names, or they may be supported
+incompatibly with Perl.  Therefore UTF-8 names that are visible to the
+filesystem, such as module names may not work.
 
 =head1 SEE ALSO