perl's encoding on output by use of the ":encoding(...)" layer.
See L<open>.
-To mark the Perl source itself as being in an particular encoding,
+To mark the Perl source itself as being in a particular encoding,
see L<encoding>.
=item Regular Expressions
BidiWS Whitespace
BidiON Other Neutrals
+=back
+
=head2 Scripts
The scripts available for C<\p{In...}> and C<\P{In...}>, for example
Yi Radicals
Yi Syllables
+=over 4
+
=item *
The special pattern C<\X> match matches any extended Unicode sequence
=back
-What doesn't yet work are the followng cases:
+What doesn't yet work are the following cases:
=over 8
[ 1] \x{...}
[ 2] \N{...}
[ 3] . \p{Is...} \P{Is...}
- [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
+ [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
[ 5] have negation
- [ 6] can use look-ahead to emulate subtracion
+ [ 6] can use look-ahead to emulate subtraction (*)
[ 7] include Letters in word characters
[ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings
[ 9] see UTR#13 Unicode Newline Guidelines
[10] should do ^ and $ also on \x{2028} and \x{2029}
+(*) Instead of [\u0370-\u03FF-[{UNASSIGNED}]] as suggested by the TR
+18 you can use negated lookahead: to match currently assigned modern
+Greek characters use for example
+
+ /(?!\p{Cn})[\x{0370}-\x{03ff}]/
+
+In other words: the matched character must not be a non-assigned
+character, but it must be in the block of modern Greek characters.
+
=item *
Level 2 - Extended Unicode Support
byteorder independent encoding. For ASCII, UTF-8 is transparent
(and we really do mean 7-bit ASCII, not any 8-bit encoding).
+The following table is from Unicode 3.1.
+
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+
+ U+0000..U+007F 00..7F
+ U+0080..U+07FF C2..DF 80..BF
+ U+0800..U+0FFF E0 A0..BF 80..BF
+ U+1000..U+FFFF E1..EF 80..BF 80..BF
+ U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
+ U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
+ U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
+
+Or, another way to look at it, as bits:
+
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+
+ 0aaaaaaa 0aaaaaaa
+ 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
+ ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
+ 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
+
+As you can see, the continuation bytes all begin with C<10>, and the
+leading bits of the start byte tells how many bytes the are in the
+encoded character.
+
=item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
UTF-16 is a 2 or 4 byte encoding. The Unicode code points
A seven-bit safe (non-eight-bit) encoding, useful if the
transport/storage is not eight-bit safe. Defined by RFC 2152.
+=back
+
=head2 Security Implications of Malformed UTF-8
Unfortunately, the specification of UTF-8 leaves some room for
the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
for more discussion of the issues.
+=head2 Using Unicode in XS
+
+If you want to handle Perl Unicode in XS extensions, you may find
+the following C APIs useful:
+
+=over 4
+
+=item *
+
+DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes
+pragma is not in effect. SvUTF8(sv) returns true is the UTF8
+flag is on, the bytes pragma is ignored. Remember that UTF8
+flag being on does not mean that there would be any characters
+of code points greater than 255 or 127 in the scalar, or that
+there even are any characters in the scalar. The UTF8 flag
+means that any characters added to the string will be encoded
+in UTF8 if the code points of the characters are greater than
+255. Not "if greater than 127", since Perl's Unicode model
+is not to use UTF-8 until it's really necessary.
+
+=item *
+
+uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
+buffer encoding the code poinqt as UTF-8, and returns a pointer
+pointing after the UTF-8 bytes.
+
+=item *
+
+utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and
+returns the Unicode character code point (and optionally the length of
+the UTF-8 byte sequence).
+
+=item *
+
+utf8_length(s, len) returns the length of the UTF-8 encoded buffer in
+characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
+scalar.
+
+=item *
+
+sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
+encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
+sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
+get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
+
+=item *
+
+is_utf8_char(buf) returns true if the buffer points to valid UTF-8.
+
+=item *
+
+is_utf8_string(buf, len) returns true if the len bytes of the buffer
+are valid UTF-8.
+
+=item *
+
+UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
+character in the buffer. UNISKIP(chr) will return the number of bytes
+required to UTF-8-encode the Unicode character code point.
+
+=item *
+
+utf8_distance(a, b) will tell the distance in characters between the
+two pointers pointing to the same UTF-8 encoded buffer.
+
+=item *
+
+utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
+is C<off> (positive or negative) Unicode characters displaced from the
+UTF-8 buffer C<s>.
+
=back
+For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
+in the Perl source code distribution.
+
=head1 SEE ALSO
-L<encoding>, L<Encode>, L<open>, L<bytes>, L<utf8>, L<perlretut>,
-L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
=cut
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