perluniintro tweaks as suggested by Jeffrey Friedl.

p4raw-id: //depot/perl@13743

diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod
index 67ce214..775609c 100644 (file)
--- a/pod/perluniintro.pod
+++ b/pod/perluniintro.pod
@@ -139,9 +139,33 @@ 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.
 
-The internal encoding of Unicode in Perl is UTF-8.  The internal
-encoding is normally hidden, however, and one need not and should not
-worry about the internal encoding at all: it is all just characters.
+Internally, Perl currently uses either whatever the native eight-bit
+character set of the platform (for example Latin-1) or UTF-8 to encode
+Unicode strings. Specifically, if all code points in the string are
+0xFF or less, Perl uses Latin-1.  Otherwise, it uses UTF-8.
+
+A user of Perl does not normally need to know nor care how Perl happens
+to encodes its internal strings, but it becomes relevant when outputting
+Unicode strings to a stream without a discipline (one with the "default
+default").  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 if warnings are turned on, a "Wide character" warning will be issued
+if those strings contain a character beyond 0x00FF.
+
+For example,
+
+      perl -w -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.
+
+To output UTF-8 always, use the ":utf8" output discipline.  Prepending
+
+      binmode(STDOUT, ":utf8");
+
+to this sample program ensures the output is completely UTF-8, and      
+of course, removes the warning.  Another way to achieve this is the
+L<encoding> pragma, discussed later in L</Legacy Encodings>.
 
 Perl 5.8.0 will also support Unicode on EBCDIC platforms.  There the
 support is somewhat harder to implement since additional conversions
@@ -149,12 +173,14 @@ are needed at every step.  Because of these difficulties the Unicode
 support won't be quite as full as in other, mainly ASCII-based,
 platforms (the Unicode support will be better than in the 5.6 series,
 which didn't work much at all for EBCDIC platform).  On EBCDIC
-platforms the internal encoding form used is UTF-EBCDIC.
+platforms the internal encoding form used 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, UTF-EBCDIC is "EBCDIC-safe").
 
 =head2 Creating Unicode
 
-To create Unicode literals, use the C<\x{...}> notation in
-doublequoted strings:
+To create Unicode literals for code points above 0xFF, use the
+C<\x{...}> notation in doublequoted strings:
 
     my $smiley = "\x{263a}";