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diff --git a/pod/perlunicode.pod b/pod/perlunicode.pod index 38cd9c7b20..37ee3d8e31 100644 --- a/pod/perlunicode.pod +++ b/pod/perlunicode.pod @@ -6,7 +6,7 @@ perlunicode - Unicode support in Perl =head2 Important Caveats -Unicode support is an extensive requirement. While perl does not +Unicode support is an extensive requirement. While Perl does not implement the Unicode standard or the accompanying technical reports from cover to cover, Perl does support many Unicode features. @@ -14,98 +14,98 @@ from cover to cover, Perl does support many Unicode features. =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. -Other encodings can be converted to perl's encoding on input, or from -perl's encoding on output by use of the ":encoding(...)" layer. -See L<open>. +Perl knows when a filehandle uses Perl's internal Unicode encodings +(UTF-8 or UTF-EBCDIC) if the filehandle is opened 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. See L<open>. -To mark the Perl source itself as being in a particular encoding, +To indicate that Perl source itself is using a particular encoding, see L<encoding>. =item Regular Expressions The regular expression compiler produces polymorphic opcodes. That is, -the pattern adapts 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 pattern adapts to the data and automatically switches to the Unicode +character scheme when presented with Unicode data--or instead uses +a traditional byte scheme when presented with byte data. =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts -As a compatibility measure, this pragma must be explicitly used to -enable recognition of UTF-8 in the Perl scripts themselves on ASCII -based machines, or to recognize UTF-EBCDIC on EBCDIC based machines. -B<NOTE: this should be the only place where an explicit C<use utf8> -is needed>. +As a compatibility measure, the C<use utf8> pragma must be explicitly +included to enable recognition of UTF-8 in the Perl scripts themselves +on ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based +machines. B<These are the only times when an explicit C<use utf8> +is needed.> You can also use the C<encoding> pragma to change the default encoding of the data in your script; see L<encoding>. =back -=head2 Byte and Character semantics +=head2 Byte and Character Semantics -Beginning with version 5.6, Perl uses logically wide characters to +Beginning with version 5.6, Perl uses logically-wide characters to represent strings internally. -In future, Perl-level operations can be expected to work with -characters rather than bytes, in general. +In future, Perl-level operations will be expected to work with +characters rather than bytes. -However, as strictly an interim compatibility measure, Perl aims to +However, as 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 +decide that the input data are characters, Perl 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. +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 -none of the program's inputs are marked as being as source of Unicode +which allowed byte semantics in Perl operations only if +none of the program's inputs were marked as being as source of Unicode character data. Such data may come from filehandles, from calls to external programs, from information provided by the system (such as %ENV), or from literals and constants in the source text. -On Windows platforms, if the C<-C> command line switch is used, (or the -${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls -will use the corresponding wide character APIs. Note that this is -currently only implemented on Windows since other platforms lack an -API standard on this area. +On Windows platforms, if the C<-C> command line switch is used or the +${^WIDE_SYSTEM_CALLS} global flag is set to C<1>, all system calls +will use the corresponding wide-character APIs. This feature is +available only on Windows to conform to the API standard already +established for that platform. -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<bytes> pragma will always, regardless of platform, 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. -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. -Thus, character semantics for these operations apply transparently; if -the input data came from a Unicode source (for example, by adding a -character encoding discipline to the filehandle whence it came, or a -literal Unicode string constant in the program), character semantics -apply; otherwise, byte semantics are in effect. To force byte semantics -on Unicode data, the C<bytes> pragma should be used. - -Notice that if you concatenate strings with byte semantics and strings -with Unicode character data, the bytes will by default be upgraded -I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a -translation to ISO 8859-1). This is done without regard to the -system's native 8-bit encoding, so to change this for systems with -non-Latin-1 (or non-EBCDIC) native encodings, use the C<encoding> -pragma, see L<encoding>. +Note that this pragma is only required while Perl defaults to byte +semantics; when character semantics become the default, this pragma +may become a no-op. See L<utf8>. + +Unless explicitly stated, Perl operators use character semantics +for Unicode data and byte semantics for non-Unicode data. +The decision to use character semantics is made transparently. If +input data comes from a Unicode source--for example, if a character +encoding discipline is added to a filehandle or a literal Unicode +string constant appears in a program--character semantics apply. +Otherwise, byte semantics are in effect. The C<bytes> pragma should +be used to force byte semantics on Unicode data. + +If strings operating under byte semantics and strings with Unicode +character data are concatenated, the new string will be upgraded to +I<ISO 8859-1 (Latin-1)>, even if the old Unicode string used EBCDIC. +This translation is done without regard to the system's native 8-bit +encoding, so to change this for systems with non-Latin-1 and +non-EBCDIC native encodings use the C<encoding> pragma. See +L<encoding>. Under character semantics, many operations that formerly operated on -bytes change to operating on characters. A character in Perl is +bytes now operate on characters. A character in Perl is logically just a number ranging from 0 to 2**31 or so. Larger -characters may encode to longer sequences of bytes internally, but -this is just an internal detail which is hidden at the Perl level. -See L<perluniintro> for more on this. +characters may encode into longer sequences of bytes internally, but +this internal detail is mostly hidden for Perl code. +See L<perluniintro> for more. -=head2 Effects of character semantics +=head2 Effects of Character Semantics Character semantics have the following effects: @@ -113,76 +113,77 @@ Character semantics have the following effects: =item * -Strings (including hash keys) and regular expression patterns may +Strings--including hash keys--and regular expression patterns may contain characters that have an ordinal value larger than 255. If you use a Unicode editor to edit your program, Unicode characters may occur directly within the literal strings in one of the various -Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but are recognized -as such (and converted to Perl's internal representation) only if the +Unicode encodings (UTF-8, UTF-EBCDIC, UCS-2, etc.), but will be recognized +as such and converted to Perl's internal representation only if the appropriate L<encoding> is specified. -You can also get Unicode characters into a string by using the C<\x{...}> -notation, putting the Unicode code for the desired character, in -hexadecimal, into the curlies. For instance, a smiley face is C<\x{263A}>. -This works only for characters with a code 0x100 and above. +Unicode characters can also be added to a string by using the C<\x{...}> +notation. The Unicode code for the desired character, in +hexadecimal, should be placed in the braces. For instance, a smiley +face is C<\x{263A}>. This encoding scheme only works for characters +with a code of 0x100 or above. Additionally, if you use charnames ':full'; -you can use the C<\N{...}> notation, putting the official Unicode character -name within the curlies. For example, C<\N{WHITE SMILING FACE}>. -This works for all characters that have names. +you can use the C<\N{...}> notation and put the official Unicode character +name within the braces, such as C<\N{WHITE SMILING FACE}>. + =item * If an appropriate L<encoding> is specified, 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.) +ideographs. Perl does not currently attempt to canonicalize variable +names. =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>).) +Regular expressions match characters instead of bytes. +"." matches a character instead of a byte. The C<\C> pattern +is provided to force a match a single byte--a "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 +bytes and match against the character properties specified in the +Unicode properties database. C<\w> can be used to match an ideograph, for instance. =item * Named Unicode properties, scripts, and block ranges may be used like -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 classes via the C<\p{}> "matches property" construct and +the C<\P{}> negation, "doesn't match property". +For instance, C<\p{Lu}> matches any character with the Unicode "Lu" (Letter, uppercase) property, while -C<\p{M}> matches any character with an "M" (mark -- accents and such) -property. Single letter properties may omit the brackets, so that can be -written C<\pM> also. Many predefined properties are available, such -as C<\p{Mirrored}> and C<\p{Tibetan}>. +C<\p{M}> matches any character with an "M" (mark--accents and such) +property. Brackets are not required for single letter properties, so +C<\p{M}> is equivalent to C<\pM>. Many predefined properties are +available, such as C<\p{Mirrored}> and C<\p{Tibetan}>. The official Unicode script and block names have spaces and dashes as -separators, but for convenience you can have dashes, spaces, and underbars -at every word division, and you need not care about correct casing. It is +separators, but for convenience you can use dashes, spaces, or +underbars, and case is unimportant. It is recommended, however, that for consistency you use the following naming: -the official Unicode script, block, or property name (see below for the -additional rules that apply to block names), with whitespace and dashes -removed, and the words "uppercase-first-lowercase-rest". That is, "Latin-1 -Supplement" becomes "Latin1Supplement". +the official Unicode script, property, or block name (see below for the +additional rules that apply to block names) with whitespace and dashes +removed, and the words "uppercase-first-lowercase-rest". "C<Latin-1 +Supplement>" thus becomes "C<Latin1Supplement>". -You can also negate both C<\p{}> and C<\P{}> by introducing a caret -(^) between the first curly and the property name: C<\p{^Tamil}> is +You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret +(^) between the first brace and the property name: C<\p{^Tamil}> is equal to C<\P{Tamil}>. Here are the basic Unicode General Category properties, followed by their -long form (you can use either, e.g. C<\p{Lu}> and C<\p{LowercaseLetter}> -are identical). +long form. You can use either; C<\p{Lu}> and C<\p{LowercaseLetter}>, +for instance, are identical. Short Long @@ -232,17 +233,17 @@ are identical). Co PrivateUse Cn Unassigned -The single-letter properties match all characters in any of the +Single-letter properties match all characters in any of the two-letter sub-properties starting with the same letter. -There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. +C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>. Because Perl hides the need for the user to understand the internal -representation of Unicode characters, it has no need to support the -somewhat messy concept of surrogates. Therefore, the C<Cs> property is not +representation of Unicode characters, there is no need to implement the +somewhat messy concept of surrogates. C<Cs> is therefore not supported. -Because scripts differ in their directionality (for example Hebrew is -written right to left), Unicode supplies these properties: +Because scripts differ in their directionality--Hebrew is +written right to left, for example--Unicode supplies these properties: Property Meaning @@ -266,15 +267,15 @@ written right to left), Unicode supplies these properties: BidiWS Whitespace BidiON Other Neutrals -For example, C<\p{BidiR}> matches all characters that are normally +For example, C<\p{BidiR}> matches characters that are normally written right to left. =back =head2 Scripts -The scripts available via C<\p{...}> and C<\P{...}>, for example -C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: +The script names which can be used by C<\p{...}> and C<\P{...}>, +such as in C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: Arabic Armenian @@ -321,7 +322,7 @@ C<\p{Latin}> or C<\p{Cyrillic}>, are as follows: Tibetan Yi -There are also extended property classes that supplement the basic +Extended property classes can supplement the basic properties, defined by the F<PropList> Unicode database: ASCIIHexDigit @@ -352,7 +353,7 @@ properties, defined by the F<PropList> Unicode database: UnifiedIdeograph WhiteSpace -and further derived properties: +and there are further derived properties: Alphabetic Lu + Ll + Lt + Lm + Lo + OtherAlphabetic Lowercase Ll + OtherLowercase @@ -369,19 +370,19 @@ and further derived properties: not explicitly assigned to a script For backward compatibility, all properties mentioned so far may have C<Is> -prepended to their name (e.g. C<\P{IsLu}> is equal to C<\P{Lu}>). +prepended to their name, so C<\P{IsLu}>, for example, is equal to C<\P{Lu}>. =head2 Blocks In addition to B<scripts>, Unicode also defines B<blocks> of characters. -The difference between scripts and blocks is that the scripts concept is -closer to natural languages, while the blocks concept is more an artificial -grouping based on groups of mostly 256 Unicode characters. For example, the -C<Latin> script contains letters from many blocks. On the other hand, the -C<Latin> script does not contain all the characters from those blocks. It -does not, for example, contain digits because digits are shared across many -scripts. Digits and other similar groups, like punctuation, are in a -category called C<Common>. +The difference between scripts and blocks is that the concept of +scripts is closer to natural languages, while the concept of blocks +is more of an artificial grouping based on groups of around 256 +Unicode characters. For example, the C<Latin> script contains letters +from many blocks but does not contain all the characters from those +blocks. It does not, for example, contain digits, because digits are +shared across many scripts. Digits and similar groups, like +punctuation, are in a category called C<Common>. For more about scripts, see the UTR #24: @@ -391,8 +392,8 @@ For more about blocks, see: http://www.unicode.org/Public/UNIDATA/Blocks.txt -Blocks names are given with the C<In> prefix. For example, the -Katakana block is referenced via C<\p{InKatakana}>. The C<In> +Block names are given with the C<In> prefix. For example, the +Katakana block is referenced via C<\p{InKatakana}>. The C<In> prefix may be omitted if there is no naming conflict with a script or any other property, but it is recommended that C<In> always be used to avoid confusion. @@ -514,66 +515,64 @@ These block names are supported: =item * -The special pattern C<\X> 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 +The special pattern C<\X> 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. C<\X> is equivalent to C<(?:\PM\pM*)>. =item * The C<tr///> operator translates characters instead of bytes. Note -that the C<tr///CU> functionality has been removed, as the interface -was a mistake. For similar functionality see pack('U0', ...) and -pack('C0', ...). +that the C<tr///CU> functionality has been removed. For similar +functionality see pack('U0', ...) and pack('C0', ...). =item * Case translation operators use the Unicode case translation tables -when provided character input. Note that C<uc()> (also known as C<\U> -in doublequoted strings) translates to uppercase, while C<ucfirst> -(also known as C<\u> in doublequoted strings) translates to titlecase -(for languages that make the distinction). Naturally the -corresponding backslash sequences have the same semantics. +when character input is provided. Note that C<uc()>, or C<\U> in +interpolated strings, translates to uppercase, while C<ucfirst>, +or C<\u> in interpolated strings, translates to titlecase in languages +that make the distinction. =item * -Most operators that deal with positions or lengths in the string will +Most operators that deal with positions or lengths in a 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. +specifically do not switch include C<vec()>, C<pack()>, and +C<unpack()>. Operators that really don't care include C<chomp()>, +operators that treats strings as a bucket of bits such as C<sort()>, +and 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 Unicode characters and integers. +since they are often used for byte-oriented formats. Again, think +"C<char>" in the C language. There is a new "C<U>" specifier +that converts between Unicode characters and integers. =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()> for Unicode strings. -(Note that this reveals the internal encoding of Unicode strings, -which is not something one normally needs to care about at all.) +The C<chr()> and C<ord()> functions work on characters, similar to +C<pack("U")> and C<unpack("U")>, I<not> C<pack("C")> and +C<unpack("C")>. C<pack("C")> and C<unpack("C")> are methods for +emulating byte-oriented C<chr()> and C<ord()> on Unicode strings. +While these methods reveal the internal encoding of Unicode strings, +that is not something one normally needs to care about at all. =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 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 B<and> the full character -wide bit complement. +The bit string operators, C<& | ^ ~>, can operate on character data. +However, for backward compatibility, such as when using bit string +operations when characters are all less than 256 in ordinal value, one +should not use C<~> (the bit complement) with characters of both +values less than 256 and values greater than 256. Most importantly, +DeMorgan's laws (C<~($x|$y) eq ~$x&~$y> and C<~($x&$y) eq ~$x|~$y>) +will not hold. The reason for this mathematical I<faux pas> is that +the complement cannot return B<both> the 8-bit (byte-wide) bit +complement B<and> the full character-wide bit complement. =item * @@ -584,26 +583,26 @@ lc(), uc(), lcfirst(), and ucfirst() work for the following cases: =item * the case mapping is from a single Unicode character to another -single Unicode character +single Unicode character, or =item * the case mapping is from a single Unicode character to more -than one Unicode character +than one Unicode character. =back -What doesn't yet work are the following cases: +The following cases do not yet work: =over 8 =item * -the "final sigma" (Greek) +the "final sigma" (Greek), and =item * -anything to with locales (Lithuanian, Turkish, Azeri) +anything to with locales (Lithuanian, Turkish, Azeri). =back @@ -615,44 +614,44 @@ And finally, C<scalar reverse()> reverses by character rather than by byte. =back -=head2 User-defined Character Properties +=head2 User-Defined Character Properties You can define your own character properties by defining subroutines -that have names beginning with "In" or "Is". The subroutines must be +whose names begin with "In" or "Is". The subroutines must be visible in the package that uses the properties. The user-defined properties can be used in the regular expression C<\p> and C<\P> constructs. -The subroutines must return a specially formatted string: one or more -newline-separated lines. Each line must be one of the following: +The subroutines must return a specially-formatted string, with one +or more newline-separated lines. Each line must be one of the following: =over 4 =item * Two hexadecimal numbers separated by horizontal whitespace (space or -tabulator characters) denoting a range of Unicode codepoints to include. +tabular characters) denoting a range of Unicode code points to include. =item * -Something to include, prefixed by "+": either an built-in character -property (prefixed by "utf8::"), for all the characters in that -property; or two hexadecimal codepoints for a range; or a single -hexadecimal codepoint. +Something to include, prefixed by "+": a built-in character +property (prefixed by "utf8::"), to represent all the characters in that +property; two hexadecimal code points for a range; or a single +hexadecimal code point. =item * -Something to exclude, prefixed by "-": either an existing character +Something to exclude, prefixed by "-": an existing character property (prefixed by "utf8::"), for all the characters in that -property; or two hexadecimal codepoints for a range; or a single -hexadecimal codepoint. +property; two hexadecimal code points for a range; or a single +hexadecimal code point. =item * -Something to negate, prefixed "!": either an existing character +Something to negate, prefixed "!": an existing character property (prefixed by "utf8::") for all the characters except the -characters in the property; or two hexadecimal codepoints for a range; -or a single hexadecimal codepoint. +characters in the property; two hexadecimal code points for a range; +or a single hexadecimal code point. =back @@ -700,16 +699,16 @@ The negation is useful for defining (surprise!) negated classes. END } -=head2 Character encodings for input and output +=head2 Character Encodings for Input and Output See L<Encode>. =head2 Unicode Regular Expression Support Level -The following list of Unicode regular expression support describes -feature by feature the Unicode support implemented in Perl as of Perl -5.8.0. The "Level N" and the section numbers refer to the Unicode -Technical Report 18, "Unicode Regular Expression Guidelines". +The following list of Unicode support for regular expressions describes +all the features currently supported. The references to "Level N" +and the section numbers refer to the Unicode Technical Report 18, +"Unicode Regular Expression Guidelines". =over 4 @@ -733,11 +732,11 @@ Level 1 - Basic Unicode Support [ 6] can use regular expression look-ahead [a] or user-defined character properties [b] to emulate subtraction [ 7] include Letters in word characters - [ 8] note that perl does Full casefolding in matching, not Simple: + [ 8] note that Perl does Full case-folding in matching, not Simple: for example U+1F88 is equivalent with U+1F000 U+03B9, not with 1F80. This difference matters for certain Greek - capital letters with certain modifiers: the Full casefolding - decomposes the letter, while the Simple casefolding would map + capital letters with certain modifiers: the Full case-folding + decomposes the letter, while the Simple case-folding would map it to a single character. [ 9] see UTR#13 Unicode Newline Guidelines [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}) @@ -795,8 +794,8 @@ Level 3 - Locale-Sensitive Support =head2 Unicode Encodings -Unicode characters are assigned to I<code points> which are abstract -numbers. To use these numbers various encodings are needed. +Unicode characters are assigned to I<code points>, which are abstract +numbers. To use these numbers, various encodings are needed. =over 4 @@ -805,8 +804,9 @@ numbers. To use these numbers various encodings are needed. UTF-8 UTF-8 is a variable-length (1 to 6 bytes, current character allocations -require 4 bytes), byteorder independent encoding. For ASCII, UTF-8 is -transparent (and we really do mean 7-bit ASCII, not another 8-bit encoding). +require 4 bytes), byte-order independent encoding. For ASCII (and we +really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is +transparent. The following table is from Unicode 3.2. @@ -823,14 +823,15 @@ The following table is from Unicode 3.2. U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF U+100000..U+10FFFF F4 80..8F 80..BF 80..BF -Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF, -the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF. -The "gaps" are caused by legal UTF-8 avoiding non-shortest encodings: -it is technically possible to UTF-8-encode a single code point in different -ways, but that is explicitly forbidden, and the shortest possible encoding -should always be used (and that is what Perl does). +Note the C<A0..BF> in C<U+0800..U+0FFF>, the C<80..9F> in +C<U+D000...U+D7FF>, the C<90..B>F in C<U+10000..U+3FFFF>, and the +C<80...8F> in C<U+100000..U+10FFFF>. The "gaps" are caused by legal +UTF-8 avoiding non-shortest encodings: it is technically possible to +UTF-8-encode a single code point in different ways, but that is +explicitly forbidden, and the shortest possible encoding should always +be used. So that's what Perl does. -Or, another way to look at it, as bits: +Another way to look at it is via bits: Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte @@ -847,25 +848,25 @@ encoded character. UTF-EBCDIC -Like UTF-8, but EBCDIC-safe, as UTF-8 is ASCII-safe. +Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. =item * UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) -(The followings items are mostly for reference, Perl doesn't -use them internally.) +The followings items are mostly for reference, Perl doesn't +use them internally. UTF-16 is a 2 or 4 byte encoding. The Unicode code points -U+0000..U+FFFF are stored in a single 16-bit unit, and the code points -U+10000..U+10FFFF in two 16-bit units. The latter case is +C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code points +C<U+10000..U+10FFFF> in two 16-bit units. The latter case is using I<surrogates>, the first 16-bit unit being the I<high surrogate>, and the second being the I<low surrogate>. -Surrogates are code points set aside to encode the U+10000..U+10FFFF +Surrogates are code points set aside to encode the C<U+10000..U+10FFFF> range of Unicode code points in pairs of 16-bit units. The I<high -surrogates> are the range U+D800..U+DBFF, and the I<low surrogates> -are the range U+DC00..U+DFFF. The surrogate encoding is +surrogates> are the range C<U+D800..U+DBFF>, and the I<low surrogates> +are the range C<U+DC00..U+DFFF>. The surrogate encoding is $hi = ($uni - 0x10000) / 0x400 + 0xD800; $lo = ($uni - 0x10000) % 0x400 + 0xDC00; @@ -875,31 +876,30 @@ and the decoding is $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); If you try to generate surrogates (for example by using chr()), you -will get a warning if warnings are turned on (C<-w> or C<use -warnings;>) because those code points are not valid for a Unicode -character. +will get a warning if warnings are turned on, because those code +points are not valid for a Unicode character. -Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 +Because of the 16-bitness, UTF-16 is byte-order dependent. UTF-16 itself can be used for in-memory computations, but if storage or -transfer is required, either UTF-16BE (Big Endian) or UTF-16LE -(Little Endian) must be chosen. +transfer is required either UTF-16BE (big-endian) or UTF-16LE +(little-endian) encodings must be chosen. This introduces another problem: what if you just know that your data -is UTF-16, but you don't know which endianness? Byte Order Marks -(BOMs) are a solution to this. A special character has been reserved +is UTF-16, but you don't know which endianness? Byte Order Marks, or +BOMs, are a solution to this. A special character has been reserved in Unicode to function as a byte order marker: the character with the -code point U+FEFF is the BOM. +code point C<U+FEFF> is the BOM. The trick is that if you read a BOM, you will know the byte order, -since if it was written on a big endian platform, you will read the -bytes 0xFE 0xFF, but if it was written on a little endian platform, -you will read the bytes 0xFF 0xFE. (And if the originating platform -was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.) +since if it was written on a big-endian platform, you will read the +bytes C<0xFE 0xFF>, but if it was written on a little-endian platform, +you will read the bytes C<0xFF 0xFE>. (And if the originating platform +was writing in UTF-8, you will read the bytes C<0xEF 0xBB 0xBF>.) The way this trick works is that the character with the code point -U+FFFE is guaranteed not to be a valid Unicode character, so the -sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in -little-endian format" and cannot be "U+FFFE, represented in big-endian +C<U+FFFE> is guaranteed not to be a valid Unicode character, so the +sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in +little-endian format" and cannot be "C<U+FFFE>, represented in big-endian format". =item * @@ -908,15 +908,15 @@ UTF-32, UTF-32BE, UTF32-LE The UTF-32 family is pretty much like the UTF-16 family, expect that the units are 32-bit, and therefore the surrogate scheme is not -needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and -0xFF 0xFE 0x00 0x00 for LE. +needed. The BOM signatures will be C<0x00 0x00 0xFE 0xFF> for BE and +C<0xFF 0xFE 0x00 0x00> for LE. =item * UCS-2, UCS-4 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit -encoding. Unlike UTF-16, UCS-2 is not extensible beyond U+FFFF, +encoding. Unlike UTF-16, UCS-2 is not extensible beyond C<U+FFFF>, because it does not use surrogates. UCS-4 is a 32-bit encoding, functionally identical to UTF-32. @@ -924,8 +924,8 @@ functionally identical to UTF-32. UTF-7 -A seven-bit safe (non-eight-bit) encoding, useful if the -transport/storage is not eight-bit safe. Defined by RFC 2152. +A seven-bit safe (non-eight-bit) encoding, which is useful if the +transport or storage is not eight-bit safe. Defined by RFC 2152. =back @@ -939,54 +939,54 @@ Malformed UTF-8 Unfortunately, the specification of UTF-8 leaves some room for interpretation of how many bytes of encoded output one should generate -from one input Unicode character. Strictly speaking, one is supposed -to always generate the shortest possible sequence of UTF-8 bytes, -because otherwise there is potential for input buffer overflow at +from one input Unicode character. Strictly speaking, the shortest +possible sequence of UTF-8 bytes should be generated, +because otherwise there is potential for an input buffer overflow at the receiving end of a UTF-8 connection. Perl always generates the -shortest length UTF-8, and with warnings on (C<-w> or C<use -warnings;>) Perl will warn about non-shortest length UTF-8 (and other -malformations, too, such as the surrogates, which are not real -Unicode code points.) +shortest length UTF-8, and with warnings on Perl will warn about +non-shortest length UTF-8 along with other malformations, such as the +surrogates, which are not real Unicode code points. =item * Regular expressions behave slightly differently between byte data and -character (Unicode data). For example, the "word character" character -class C<\w> will work differently when the data is all eight-bit bytes -or when the data is Unicode. +character (Unicode) data. For example, the "word character" character +class C<\w> will work differently depending on if data is eight-bit bytes +or Unicode. -In the first case, the set of C<\w> characters is either small (the -default set of alphabetic characters, digits, and the "_"), or, if you +In the first case, the set of C<\w> characters is either small--the +default set of alphabetic characters, digits, and the "_"--or, if you are using a locale (see L<perllocale>), the C<\w> might contain a few more letters according to your language and country. -In the second case, the C<\w> set of characters is much, much larger, -and most importantly, even in the set of the first 256 characters, it -will most probably be different: as opposed to most locales (which are -specific to a language and country pair) Unicode classifies all the -characters that are letters as C<\w>. For example: your locale might +In the second case, the C<\w> set of characters is much, much larger. +Most importantly, even in the set of the first 256 characters, it +will probably match different characters: unlike most locales, +which are specific to a language and country pair, Unicode classifies all +the characters that are letters as C<\w>. For example, your locale might not think that LATIN SMALL LETTER ETH is a letter (unless you happen to speak Icelandic), but Unicode does. -As discussed elsewhere, Perl tries to stand one leg (two legs, as -camels are quadrupeds?) in two worlds: the old world of bytes and the new +As discussed elsewhere, Perl has one foot (two hooves?) planted in +each of two worlds: the old world of bytes and the new world of characters, upgrading from bytes to characters when necessary. -If your legacy code is not explicitly using Unicode, no automatic -switchover to characters should happen, and characters shouldn't get -downgraded back to bytes, either. It is possible to accidentally mix -bytes and characters, however (see L<perluniintro>), in which case the -C<\w> might start behaving differently. Review your code. +If your legacy code does not explicitly use Unicode, no automatic +switch-over to characters should happen. Characters shouldn't get +downgraded to bytes, either. It is possible to accidentally mix +bytes and characters, however (see L<perluniintro>), in which case +C<\w> in regular expressions might start behaving differently. Review +your code. =back =head2 Unicode in Perl on EBCDIC -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 +The way Unicode is handled on EBCDIC platforms is still +experimental. On such platforms, references to UTF-8 encoding in this +document and elsewhere should be read as meaning the UTF-EBCDIC +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 +":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for more discussion of the issues. @@ -1001,113 +1001,114 @@ there are a couple of exceptions: If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG) contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), -the default encoding of your STDIN, STDOUT, and STDERR, and of -B<any subsequent file open>, is UTF-8. +the default encodings of your STDIN, STDOUT, and STDERR, and of +B<any subsequent file open>, are considered to be UTF-8. =item * -Perl tries really hard to work both with Unicode and the old byte -oriented world: most often this is nice, but sometimes this causes -problems. +Perl tries really hard to work both with Unicode and the old +byte-oriented world. Most often this is nice, but sometimes Perl's +straddling of the proverbial fence causes problems. =back =head2 Using Unicode in XS If you want to handle Perl Unicode in XS extensions, you may find -the following C APIs useful (see perlapi for details): +the following C APIs useful. See L<perlapi> for details. =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. The UTF8 flag being on does B<not> mean that +C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes pragma +is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> flag is on; the +bytes pragma is ignored. The C<UTF8> flag being on does B<not> mean that there are any characters of code points greater than 255 (or 127) in -the scalar, or that there even are any characters in the scalar. -What the UTF8 flag means is that the sequence of octets in the +the scalar or that there are even any characters in the scalar. +What the C<UTF8> flag means is that the sequence of octets in the representation of the scalar is the sequence of UTF-8 encoded -code points of the characters of a string. The UTF8 flag being +code points of the characters of a string. The C<UTF8> flag being off means that each octet in this representation encodes a single -character with codepoint 0..255 within the string. Perl's Unicode -model is not to use UTF-8 until it's really necessary. +character with code point 0..255 within the string. Perl's Unicode +model is not to use UTF-8 until it is absolutely necessary. =item * -uvuni_to_utf8(buf, chr) writes a Unicode character code point into a +C<uvuni_to_utf8(buf, chr>) writes a Unicode character code point into a buffer encoding the code point 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). +C<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(start, end) returns the length of the UTF-8 encoded buffer -in characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded +C<utf8_length(start, end)> returns the length of the UTF-8 encoded buffer +in characters. C<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(). -Note that none of these are to be used as general purpose encoding/decoding -interfaces: use Encode for that. sv_utf8_upgrade() is affected by the -encoding pragma, but sv_utf8_downgrade() is not (since the encoding -pragma is designed to be a one-way street). +C<sv_utf8_upgrade(sv)> converts the string of the scalar to its UTF-8 +encoded form. C<sv_utf8_downgrade(sv)> does the opposite, if +possible. C<sv_utf8_encode(sv)> is like sv_utf8_upgrade except that +it does not set the C<UTF8> flag. C<sv_utf8_decode()> does the +opposite of C<sv_utf8_encode()>. Note that none of these are to be +used as general-purpose encoding or decoding interfaces: C<use Encode> +for that. C<sv_utf8_upgrade()> is affected by the encoding pragma +but C<sv_utf8_downgrade()> is not (since the encoding pragma is +designed to be a one-way street). =item * -is_utf8_char(s) returns true if the pointer points to a valid UTF-8 +C<is_utf8_char(s)> returns true if the pointer points to a valid UTF-8 character. =item * -is_utf8_string(buf, len) returns true if the len bytes of the buffer +C<is_utf8_string(buf, len)> returns true if C<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. UTF8SKIP() +C<UTF8SKIP(buf)> will return the number of bytes in the UTF-8 encoded +character in the buffer. C<UNISKIP(chr)> will return the number of bytes +required to UTF-8-encode the Unicode character code point. C<UTF8SKIP()> is useful for example for iterating over the characters of a UTF-8 -encoded buffer; UNISKIP() is useful for example in computing +encoded buffer; C<UNISKIP()> is useful, for example, in computing the size required for a UTF-8 encoded buffer. =item * -utf8_distance(a, b) will tell the distance in characters between the +C<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>. Be careful not to overstep the buffer: utf8_hop() -will merrily run off the end or the beginning if told to do so. +C<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>. Be careful not to overstep the buffer: +C<utf8_hop()> will merrily run off the end or the beginning of the +buffer if told to do so. =item * -pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv, -ssv, pvlim, flags) are useful for debug output of Unicode strings and -scalars. By default they are useful only for debug: they display -B<all> characters as hexadecimal code points, but with the flags -UNI_DISPLAY_ISPRINT and UNI_DISPLAY_BACKSLASH you can make the output -more readable. +C<pv_uni_display(dsv, spv, len, pvlim, flags)> and +C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the +output of Unicode strings and scalars. By default they are useful +only for debugging--they display B<all> characters as hexadecimal code +points--but with the flags C<UNI_DISPLAY_ISPRINT> and +C<UNI_DISPLAY_BACKSLASH> you can make the output more readable. =item * -ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2) can be used to -compare two strings case-insensitively in Unicode. -(For case-sensitive comparisons you can just use memEQ() and memNE() -as usual.) +C<ibcmp_utf8(s1, pe1, u1, l1, u1, s2, pe2, l2, u2)> can be used to +compare two strings case-insensitively in Unicode. For case-sensitive +comparisons you can just use C<memEQ()> and C<memNE()> as usual. =back @@ -1116,40 +1117,41 @@ in the Perl source code distribution. =head1 BUGS -=head2 Interaction with locales +=head2 Interaction with Locales -Use of locales with Unicode data 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. Use of locales with Unicode is discouraged. +Use of locales with Unicode data may lead to odd results. Currently, +Perl attempts to attach 8-bit locale info to characters in the range +0..255, but this technique is demonstrably incorrect for locales that +use characters above that range when mapped into Unicode. Perl's +Unicode support will also tend to run slower. Use of locales with +Unicode is discouraged. -=head2 Interaction with extensions +=head2 Interaction with Extensions -When perl exchanges data with an extension, the extension should be +When Perl exchanges data with an extension, the extension should be able to understand the UTF-8 flag and act accordingly. If the -extension doesn't know about the flag, the risk is high that it will -return data that are incorrectly flagged. +extension doesn't know about the flag, it's likely that the extension +will return incorrectly-flagged data. So if you're working with Unicode data, consult the documentation of every module you're using if there are any issues with Unicode data exchange. If the documentation does not talk about Unicode at all, suspect the worst and probably look at the source to learn how the -module is implemented. Modules written completely in perl shouldn't +module is implemented. Modules written completely in Perl shouldn't cause problems. Modules that directly or indirectly access code written in other programming languages are at risk. -For affected functions the simple strategy to avoid data corruption is +For affected functions, the simple strategy to avoid data corruption is to always make the encoding of the exchanged data explicit. Choose an -encoding you know the extension can handle. Convert arguments passed +encoding that you know the extension can handle. Convert arguments passed to the extensions to that encoding and convert results back from that encoding. Write wrapper functions that do the conversions for you, so you can later change the functions when the extension catches up. -To provide an example let's say the popular Foo::Bar::escape_html +To provide an example, let's say the popular Foo::Bar::escape_html function doesn't deal with Unicode data yet. The wrapper function would convert the argument to raw UTF-8 and convert the result back to -perl's internal representation like so: +Perl's internal representation like so: sub my_escape_html ($) { my($what) = shift; @@ -1187,7 +1189,7 @@ DB_File::filter_store_key and family. Look out for such filters in the documentation of your extensions, they can make the transition to Unicode data much easier. -=head2 speed +=head2 Speed Some functions are slower when working on UTF-8 encoded strings than on byte encoded strings. All functions that need to hop over @@ -1214,10 +1216,10 @@ following benchmark: SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877) SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329) -The numbers show an incredible slowness on long UTF-8 strings and you -should carefully avoid to use these functions within tight loops. For -example if you want to iterate over characters, it is infinitely -better to split into an array than to use substr, as the following +The numbers show an incredible slowness on long UTF-8 strings. You +should carefully avoid using these functions in tight loops. If you +want to iterate over characters, the superior coding technique would +split the characters into an array instead of using substr, as the following benchmark shows: % perl -e ' @@ -1239,8 +1241,9 @@ benchmark shows: SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658) SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5) -You see, the algorithm based on substr() was faster with byte encoded -data but it is pathologically slow with UTF-8 data. +Even though the algorithm based on C<substr()> is faster than +C<split()> for byte-encoded data, it pales in comparison to the speed +of C<split()> when used with UTF-8 data. =head1 SEE ALSO |