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1 | =head1 NAME |
2 | |
3 | perlunicode - Unicode support in Perl |
4 | |
5 | =head1 DESCRIPTION |
6 | |
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7 | =head2 Important Caveats |
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8 | |
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9 | Unicode support is an extensive requirement. While perl does not |
10 | implement the Unicode standard or the accompanying technical reports |
11 | from cover to cover, Perl does support many Unicode features. |
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12 | |
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13 | =over 4 |
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14 | |
15 | =item Input and Output Disciplines |
16 | |
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17 | A filehandle can be marked as containing perl's internal Unicode |
18 | encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer. |
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19 | Other encodings can be converted to perl's encoding on input, or from |
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20 | perl's encoding on output by use of the ":encoding(...)" layer. |
21 | See L<open>. |
22 | |
23 | To mark the Perl source itself as being in an particular encoding, |
24 | see L<encoding>. |
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25 | |
26 | =item Regular Expressions |
27 | |
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28 | The regular expression compiler produces polymorphic opcodes. That is, |
29 | the pattern adapts to the data and automatically switch to the Unicode |
30 | character scheme when presented with Unicode data, or a traditional |
31 | byte scheme when presented with byte data. |
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32 | |
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33 | =item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts |
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34 | |
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35 | The C<utf8> pragma implements the tables used for Unicode support. |
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36 | However, these tables are automatically loaded on demand, so the |
37 | C<utf8> pragma should not normally be used. |
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38 | |
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39 | As a compatibility measure, this pragma must be explicitly used to |
40 | enable recognition of UTF-8 in the Perl scripts themselves on ASCII |
41 | based machines or recognize UTF-EBCDIC on EBCDIC based machines. |
42 | B<NOTE: this should be the only place where an explicit C<use utf8> |
43 | is needed>. |
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44 | |
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45 | You can also use the C<encoding> pragma to change the default encoding |
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46 | of the data in your script; see L<encoding>. |
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47 | |
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48 | =back |
49 | |
50 | =head2 Byte and Character semantics |
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51 | |
52 | Beginning with version 5.6, Perl uses logically wide characters to |
53 | represent strings internally. This internal representation of strings |
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54 | uses either the UTF-8 or the UTF-EBCDIC encoding. |
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55 | |
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56 | In future, Perl-level operations can be expected to work with |
57 | characters rather than bytes, in general. |
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58 | |
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59 | However, as strictly an interim compatibility measure, Perl aims to |
60 | provide a safe migration path from byte semantics to character |
61 | semantics for programs. For operations where Perl can unambiguously |
62 | decide that the input data is characters, Perl now switches to |
63 | character semantics. For operations where this determination cannot |
64 | be made without additional information from the user, Perl decides in |
65 | favor of compatibility, and chooses to use byte semantics. |
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66 | |
67 | This behavior preserves compatibility with earlier versions of Perl, |
68 | which allowed byte semantics in Perl operations, but only as long as |
69 | none of the program's inputs are marked as being as source of Unicode |
70 | character data. Such data may come from filehandles, from calls to |
71 | external programs, from information provided by the system (such as %ENV), |
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72 | or from literals and constants in the source text. |
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73 | |
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74 | On Windows platforms, if the C<-C> command line switch is used, (or the |
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75 | ${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls |
76 | will use the corresponding wide character APIs. Note that this is |
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77 | currently only implemented on Windows since other platforms lack an |
78 | API standard on this area. |
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79 | |
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80 | Regardless of the above, the C<bytes> pragma can always be used to |
81 | force byte semantics in a particular lexical scope. See L<bytes>. |
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82 | |
83 | The C<utf8> pragma is primarily a compatibility device that enables |
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84 | recognition of UTF-(8|EBCDIC) in literals encountered by the parser. |
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85 | Note that this pragma is only required until a future version of Perl |
86 | in which character semantics will become the default. This pragma may |
87 | then become a no-op. See L<utf8>. |
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88 | |
89 | Unless mentioned otherwise, Perl operators will use character semantics |
90 | when they are dealing with Unicode data, and byte semantics otherwise. |
91 | Thus, character semantics for these operations apply transparently; if |
92 | the input data came from a Unicode source (for example, by adding a |
93 | character encoding discipline to the filehandle whence it came, or a |
94 | literal UTF-8 string constant in the program), character semantics |
95 | apply; otherwise, byte semantics are in effect. To force byte semantics |
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96 | on Unicode data, the C<bytes> pragma should be used. |
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97 | |
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98 | Notice that if you concatenate strings with byte semantics and strings |
99 | with Unicode character data, the bytes will by default be upgraded |
100 | I<as if they were ISO 8859-1 (Latin-1)> (or if in EBCDIC, after a |
101 | translation to ISO 8859-1). To change this, use the C<encoding> |
102 | pragma, see L<encoding>. |
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103 | |
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104 | Under character semantics, many operations that formerly operated on |
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105 | bytes change to operating on characters. For ASCII data this makes no |
106 | difference, because UTF-8 stores ASCII in single bytes, but for any |
107 | character greater than C<chr(127)>, the character B<may> be stored in |
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108 | a sequence of two or more bytes, all of which have the high bit set. |
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109 | |
110 | For C1 controls or Latin 1 characters on an EBCDIC platform the |
111 | character may be stored in a UTF-EBCDIC multi byte sequence. But by |
112 | and large, the user need not worry about this, because Perl hides it |
113 | from the user. A character in Perl is logically just a number ranging |
114 | from 0 to 2**32 or so. Larger characters encode to longer sequences |
115 | of bytes internally, but again, this is just an internal detail which |
116 | is hidden at the Perl level. |
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117 | |
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118 | =head2 Effects of character semantics |
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119 | |
120 | Character semantics have the following effects: |
121 | |
122 | =over 4 |
123 | |
124 | =item * |
125 | |
126 | Strings and patterns may contain characters that have an ordinal value |
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127 | larger than 255. |
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128 | |
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129 | Presuming you use a Unicode editor to edit your program, such |
130 | characters will typically occur directly within the literal strings as |
131 | UTF-8 (or UTF-EBCDIC on EBCDIC platforms) characters, but you can also |
132 | specify a particular character with an extension of the C<\x> |
133 | notation. UTF-X characters are specified by putting the hexadecimal |
134 | code within curlies after the C<\x>. For instance, a Unicode smiley |
135 | face is C<\x{263A}>. |
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136 | |
137 | =item * |
138 | |
139 | Identifiers within the Perl script may contain Unicode alphanumeric |
140 | characters, including ideographs. (You are currently on your own when |
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141 | it comes to using the canonical forms of characters--Perl doesn't |
142 | (yet) attempt to canonicalize variable names for you.) |
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143 | |
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144 | =item * |
145 | |
146 | Regular expressions match characters instead of bytes. For instance, |
147 | "." matches a character instead of a byte. (However, the C<\C> pattern |
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148 | is provided to force a match a single byte ("C<char>" in C, hence C<\C>).) |
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149 | |
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150 | =item * |
151 | |
152 | Character classes in regular expressions match characters instead of |
153 | bytes, and match against the character properties specified in the |
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154 | Unicode properties database. So C<\w> can be used to match an |
155 | ideograph, for instance. |
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156 | |
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157 | =item * |
158 | |
159 | Named Unicode properties and block ranges make be used as character |
160 | classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't |
161 | match property) constructs. For instance, C<\p{Lu}> matches any |
162 | character with the Unicode uppercase property, while C<\p{M}> matches |
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163 | any mark character. Single letter properties may omit the brackets, |
164 | so that can be written C<\pM> also. Many predefined character classes |
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165 | are available, such as C<\p{IsMirrored}> and C<\p{InTibetan}>. |
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166 | |
167 | The C<\p{Is...}> test for "general properties" such as "letter", |
168 | "digit", while the C<\p{In...}> test for Unicode scripts and blocks. |
169 | |
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170 | The official Unicode script and block names have spaces and dashes and |
171 | separators, but for convenience you can have dashes, spaces, and |
172 | underbars at every word division, and you need not care about correct |
173 | casing. It is recommended, however, that for consistency you use the |
174 | following naming: the official Unicode script, block, or property name |
175 | (see below for the additional rules that apply to block names), |
176 | with whitespace and dashes replaced with underbar, and the words |
177 | "uppercase-first-lowercase-rest". That is, "Latin-1 Supplement" |
178 | becomes "Latin_1_Supplement". |
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179 | |
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180 | You can also negate both C<\p{}> and C<\P{}> by introducing a caret |
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181 | (^) between the first curly and the property name: C<\p{^In_Tamil}> is |
182 | equal to C<\P{In_Tamil}>. |
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183 | |
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184 | The C<In> and C<Is> can be left out: C<\p{Greek}> is equal to |
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185 | C<\p{In_Greek}>, C<\P{Pd}> is equal to C<\P{Pd}>. |
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186 | |
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187 | Short Long |
188 | |
189 | L Letter |
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190 | Lu Uppercase_Letter |
191 | Ll Lowercase_Letter |
192 | Lt Titlecase_Letter |
193 | Lm Modifier_Letter |
194 | Lo Other_Letter |
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195 | |
196 | M Mark |
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197 | Mn Nonspacing_Mark |
198 | Mc Spacing_Mark |
199 | Me Enclosing_Mark |
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200 | |
201 | N Number |
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202 | Nd Decimal_Number |
203 | Nl Letter_Number |
204 | No Other_Number |
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205 | |
206 | P Punctuation |
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207 | Pc Connector_Punctuation |
208 | Pd Dash_Punctuation |
209 | Ps Open_Punctuation |
210 | Pe Close_Punctuation |
211 | Pi Initial_Punctuation |
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212 | (may behave like Ps or Pe depending on usage) |
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213 | Pf Final_Punctuation |
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214 | (may behave like Ps or Pe depending on usage) |
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215 | Po Other_Punctuation |
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216 | |
217 | S Symbol |
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218 | Sm Math_Symbol |
219 | Sc Currency_Symbol |
220 | Sk Modifier_Symbol |
221 | So Other_Symbol |
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222 | |
223 | Z Separator |
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224 | Zs Space_Separator |
225 | Zl Line_Separator |
226 | Zp Paragraph_Separator |
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227 | |
228 | C Other |
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229 | Cc Control |
230 | Cf Format |
231 | Cs Surrogate |
232 | Co Private_Use |
233 | Cn Unassigned |
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234 | |
235 | There's also C<L&> which is an alias for C<Ll>, C<Lu>, and C<Lt>. |
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236 | |
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237 | The following reserved ranges have C<In> tests: |
238 | |
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239 | CJK_Ideograph_Extension_A |
240 | CJK_Ideograph |
241 | Hangul_Syllable |
242 | Non_Private_Use_High_Surrogate |
243 | Private_Use_High_Surrogate |
244 | Low_Surrogate |
245 | Private_Surrogate |
246 | CJK_Ideograph_Extension_B |
247 | Plane_15_Private_Use |
248 | Plane_16_Private_Use |
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249 | |
250 | For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true. |
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251 | (Handling of surrogates is not implemented yet, because Perl |
252 | uses UTF-8 and not UTF-16 internally to represent Unicode.) |
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253 | |
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254 | Additionally, because scripts differ in their directionality |
255 | (for example Hebrew is written right to left), all characters |
256 | have their directionality defined: |
257 | |
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258 | BidiL Left-to-Right |
259 | BidiLRE Left-to-Right Embedding |
260 | BidiLRO Left-to-Right Override |
261 | BidiR Right-to-Left |
262 | BidiAL Right-to-Left Arabic |
263 | BidiRLE Right-to-Left Embedding |
264 | BidiRLO Right-to-Left Override |
265 | BidiPDF Pop Directional Format |
266 | BidiEN European Number |
267 | BidiES European Number Separator |
268 | BidiET European Number Terminator |
269 | BidiAN Arabic Number |
270 | BidiCS Common Number Separator |
271 | BidiNSM Non-Spacing Mark |
272 | BidiBN Boundary Neutral |
273 | BidiB Paragraph Separator |
274 | BidiS Segment Separator |
275 | BidiWS Whitespace |
276 | BidiON Other Neutrals |
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277 | |
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278 | =head2 Scripts |
279 | |
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280 | The scripts available for C<\p{In...}> and C<\P{In...}>, for example |
281 | \p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>: |
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282 | |
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283 | Arabic |
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284 | Armenian |
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285 | Bengali |
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286 | Bopomofo |
287 | Canadian-Aboriginal |
288 | Cherokee |
289 | Cyrillic |
290 | Deseret |
291 | Devanagari |
292 | Ethiopic |
293 | Georgian |
294 | Gothic |
295 | Greek |
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296 | Gujarati |
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297 | Gurmukhi |
298 | Han |
299 | Hangul |
300 | Hebrew |
301 | Hiragana |
302 | Inherited |
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303 | Kannada |
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304 | Katakana |
305 | Khmer |
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306 | Lao |
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307 | Latin |
308 | Malayalam |
309 | Mongolian |
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310 | Myanmar |
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311 | Ogham |
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312 | Old-Italic |
313 | Oriya |
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314 | Runic |
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315 | Sinhala |
316 | Syriac |
317 | Tamil |
318 | Telugu |
319 | Thaana |
320 | Thai |
321 | Tibetan |
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322 | Yi |
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323 | |
324 | There are also extended property classes that supplement the basic |
325 | properties, defined by the F<PropList> Unicode database: |
326 | |
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327 | ASCII_Hex_Digit |
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328 | Bidi_Control |
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329 | Dash |
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330 | Diacritic |
331 | Extender |
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332 | Hex_Digit |
333 | Hyphen |
334 | Ideographic |
335 | Join_Control |
336 | Noncharacter_Code_Point |
337 | Other_Alphabetic |
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338 | Other_Lowercase |
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339 | Other_Math |
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340 | Other_Uppercase |
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341 | Quotation_Mark |
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342 | White_Space |
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343 | |
344 | and further derived properties: |
345 | |
346 | Alphabetic Lu + Ll + Lt + Lm + Lo + Other_Alphabetic |
347 | Lowercase Ll + Other_Lowercase |
348 | Uppercase Lu + Other_Uppercase |
349 | Math Sm + Other_Math |
350 | |
351 | ID_Start Lu + Ll + Lt + Lm + Lo + Nl |
352 | ID_Continue ID_Start + Mn + Mc + Nd + Pc |
353 | |
354 | Any Any character |
355 | Assigned Any non-Cn character |
356 | Common Any character (or unassigned code point) |
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357 | not explicitly assigned to a script |
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358 | |
359 | =head2 Blocks |
360 | |
361 | In addition to B<scripts>, Unicode also defines B<blocks> of |
362 | characters. The difference between scripts and blocks is that the |
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363 | scripts concept is closer to natural languages, while the blocks |
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364 | concept is more an artificial grouping based on groups of 256 Unicode |
365 | characters. For example, the C<Latin> script contains letters from |
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366 | many blocks. On the other hand, the C<Latin> script does not contain |
367 | all the characters from those blocks, it does not for example contain |
368 | digits because digits are shared across many scripts. Digits and |
369 | other similar groups, like punctuation, are in a category called |
370 | C<Common>. |
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371 | |
372 | For more about scripts see the UTR #24: |
373 | http://www.unicode.org/unicode/reports/tr24/ |
374 | For more about blocks see |
375 | http://www.unicode.org/Public/UNIDATA/Blocks.txt |
376 | |
377 | Because there are overlaps in naming (there are, for example, both |
378 | a script called C<Katakana> and a block called C<Katakana>, the block |
379 | version has C<Block> appended to its name, C<\p{InKatakanaBlock}>. |
380 | |
381 | Notice that this definition was introduced in Perl 5.8.0: in Perl |
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382 | 5.6 only the blocks were used; in Perl 5.8.0 scripts became the |
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383 | preferential Unicode character class definition; this meant that |
384 | the definitions of some character classes changed (the ones in the |
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385 | below list that have the C<Block> appended). |
386 | |
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387 | Alphabetic Presentation Forms |
388 | Arabic Block |
389 | Arabic Presentation Forms-A |
390 | Arabic Presentation Forms-B |
391 | Armenian Block |
392 | Arrows |
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393 | Basic Latin |
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394 | Bengali Block |
395 | Block Elements |
396 | Bopomofo Block |
397 | Bopomofo Extended |
398 | Box Drawing |
399 | Braille Patterns |
400 | Byzantine Musical Symbols |
401 | CJK Compatibility |
402 | CJK Compatibility Forms |
403 | CJK Compatibility Ideographs |
404 | CJK Compatibility Ideographs Supplement |
405 | CJK Radicals Supplement |
406 | CJK Symbols and Punctuation |
407 | CJK Unified Ideographs |
408 | CJK Unified Ideographs Extension A |
409 | CJK Unified Ideographs Extension B |
410 | Cherokee Block |
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411 | Combining Diacritical Marks |
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412 | Combining Half Marks |
413 | Combining Marks for Symbols |
414 | Control Pictures |
415 | Currency Symbols |
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416 | Cyrillic Block |
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417 | Deseret Block |
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418 | Devanagari Block |
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419 | Dingbats |
420 | Enclosed Alphanumerics |
421 | Enclosed CJK Letters and Months |
422 | Ethiopic Block |
423 | General Punctuation |
424 | Geometric Shapes |
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425 | Georgian Block |
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426 | Gothic Block |
427 | Greek Block |
428 | Greek Extended |
429 | Gujarati Block |
430 | Gurmukhi Block |
431 | Halfwidth and Fullwidth Forms |
432 | Hangul Compatibility Jamo |
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433 | Hangul Jamo |
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434 | Hangul Syllables |
435 | Hebrew Block |
436 | High Private Use Surrogates |
437 | High Surrogates |
438 | Hiragana Block |
439 | IPA Extensions |
440 | Ideographic Description Characters |
441 | Kanbun |
442 | Kangxi Radicals |
443 | Kannada Block |
444 | Katakana Block |
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445 | Khmer Block |
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446 | Lao Block |
447 | Latin 1 Supplement |
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448 | Latin Extended Additional |
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449 | Latin Extended-A |
450 | Latin Extended-B |
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451 | Letterlike Symbols |
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452 | Low Surrogates |
453 | Malayalam Block |
454 | Mathematical Alphanumeric Symbols |
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455 | Mathematical Operators |
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456 | Miscellaneous Symbols |
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457 | Miscellaneous Technical |
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458 | Mongolian Block |
459 | Musical Symbols |
460 | Myanmar Block |
461 | Number Forms |
462 | Ogham Block |
463 | Old Italic Block |
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464 | Optical Character Recognition |
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465 | Oriya Block |
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466 | Private Use |
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467 | Runic Block |
468 | Sinhala Block |
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469 | Small Form Variants |
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470 | Spacing Modifier Letters |
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471 | Specials |
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472 | Superscripts and Subscripts |
473 | Syriac Block |
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474 | Tags |
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475 | Tamil Block |
476 | Telugu Block |
477 | Thaana Block |
478 | Thai Block |
479 | Tibetan Block |
480 | Unified Canadian Aboriginal Syllabics |
481 | Yi Radicals |
482 | Yi Syllables |
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483 | |
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484 | =item * |
485 | |
486 | The special pattern C<\X> match matches any extended Unicode sequence |
487 | (a "combining character sequence" in Standardese), where the first |
488 | character is a base character and subsequent characters are mark |
489 | characters that apply to the base character. It is equivalent to |
490 | C<(?:\PM\pM*)>. |
491 | |
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492 | =item * |
493 | |
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494 | The C<tr///> operator translates characters instead of bytes. Note |
495 | that the C<tr///CU> functionality has been removed, as the interface |
496 | was a mistake. For similar functionality see pack('U0', ...) and |
497 | pack('C0', ...). |
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498 | |
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499 | =item * |
500 | |
501 | Case translation operators use the Unicode case translation tables |
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502 | when provided character input. Note that C<uc()> (also known as C<\U> |
503 | in doublequoted strings) translates to uppercase, while C<ucfirst> |
504 | (also known as C<\u> in doublequoted strings) translates to titlecase |
505 | (for languages that make the distinction). Naturally the |
506 | corresponding backslash sequences have the same semantics. |
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507 | |
508 | =item * |
509 | |
510 | Most operators that deal with positions or lengths in the string will |
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511 | automatically switch to using character positions, including |
512 | C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>, |
513 | C<sprintf()>, C<write()>, and C<length()>. Operators that |
514 | specifically don't switch include C<vec()>, C<pack()>, and |
515 | C<unpack()>. Operators that really don't care include C<chomp()>, as |
516 | well as any other operator that treats a string as a bucket of bits, |
517 | such as C<sort()>, and the operators dealing with filenames. |
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518 | |
519 | =item * |
520 | |
521 | The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change, |
522 | since they're often used for byte-oriented formats. (Again, think |
523 | "C<char>" in the C language.) However, there is a new "C<U>" specifier |
524 | that will convert between UTF-8 characters and integers. (It works |
525 | outside of the utf8 pragma too.) |
526 | |
527 | =item * |
528 | |
529 | The C<chr()> and C<ord()> functions work on characters. This is like |
530 | C<pack("U")> and C<unpack("U")>, not like C<pack("C")> and |
531 | C<unpack("C")>. In fact, the latter are how you now emulate |
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532 | byte-oriented C<chr()> and C<ord()> for Unicode strings. |
533 | (Note that this reveals the internal UTF-8 encoding of strings and |
534 | you are not supposed to do that unless you know what you are doing.) |
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535 | |
536 | =item * |
537 | |
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538 | The bit string operators C<& | ^ ~> can operate on character data. |
539 | However, for backward compatibility reasons (bit string operations |
75daf61c |
540 | when the characters all are less than 256 in ordinal value) one should |
541 | not mix C<~> (the bit complement) and characters both less than 256 and |
a1ca4561 |
542 | equal or greater than 256. Most importantly, the DeMorgan's laws |
543 | (C<~($x|$y) eq ~$x&~$y>, C<~($x&$y) eq ~$x|~$y>) won't hold. |
544 | Another way to look at this is that the complement cannot return |
75daf61c |
545 | B<both> the 8-bit (byte) wide bit complement B<and> the full character |
a1ca4561 |
546 | wide bit complement. |
547 | |
548 | =item * |
549 | |
983ffd37 |
550 | lc(), uc(), lcfirst(), and ucfirst() work for the following cases: |
551 | |
552 | =over 8 |
553 | |
554 | =item * |
555 | |
556 | the case mapping is from a single Unicode character to another |
557 | single Unicode character |
558 | |
559 | =item * |
560 | |
561 | the case mapping is from a single Unicode character to more |
562 | than one Unicode character |
563 | |
564 | =back |
565 | |
566 | What doesn't yet work are the followng cases: |
567 | |
568 | =over 8 |
569 | |
570 | =item * |
571 | |
572 | the "final sigma" (Greek) |
573 | |
574 | =item * |
575 | |
576 | anything to with locales (Lithuanian, Turkish, Azeri) |
577 | |
578 | =back |
579 | |
580 | See the Unicode Technical Report #21, Case Mappings, for more details. |
ac1256e8 |
581 | |
582 | =item * |
583 | |
393fec97 |
584 | And finally, C<scalar reverse()> reverses by character rather than by byte. |
585 | |
586 | =back |
587 | |
8cbd9a7a |
588 | =head2 Character encodings for input and output |
589 | |
7221edc9 |
590 | See L<Encode>. |
8cbd9a7a |
591 | |
393fec97 |
592 | =head1 CAVEATS |
593 | |
594 | As of yet, there is no method for automatically coercing input and |
b3419ed8 |
595 | output to some encoding other than UTF-8 or UTF-EBCDIC. This is planned |
596 | in the near future, however. |
393fec97 |
597 | |
8cbd9a7a |
598 | Whether an arbitrary piece of data will be treated as "characters" or |
599 | "bytes" by internal operations cannot be divined at the current time. |
393fec97 |
600 | |
601 | Use of locales with utf8 may lead to odd results. Currently there is |
602 | some attempt to apply 8-bit locale info to characters in the range |
603 | 0..255, but this is demonstrably incorrect for locales that use |
604 | characters above that range (when mapped into Unicode). It will also |
605 | tend to run slower. Avoidance of locales is strongly encouraged. |
606 | |
776f8809 |
607 | =head1 UNICODE REGULAR EXPRESSION SUPPORT LEVEL |
608 | |
609 | The following list of Unicode regular expression support describes |
610 | feature by feature the Unicode support implemented in Perl as of Perl |
611 | 5.8.0. The "Level N" and the section numbers refer to the Unicode |
612 | Technical Report 18, "Unicode Regular Expression Guidelines". |
613 | |
614 | =over 4 |
615 | |
616 | =item * |
617 | |
618 | Level 1 - Basic Unicode Support |
619 | |
620 | 2.1 Hex Notation - done [1] |
621 | Named Notation - done [2] |
622 | 2.2 Categories - done [3][4] |
623 | 2.3 Subtraction - MISSING [5][6] |
624 | 2.4 Simple Word Boundaries - done [7] |
90a59240 |
625 | 2.5 Simple Loose Matches - done [8] |
776f8809 |
626 | 2.6 End of Line - MISSING [9][10] |
627 | |
628 | [ 1] \x{...} |
629 | [ 2] \N{...} |
630 | [ 3] . \p{Is...} \P{Is...} |
631 | [ 4] now scripts (see UTR#24 Script Names) in addition to blocks |
632 | [ 5] have negation |
633 | [ 6] can use look-ahead to emulate subtracion |
634 | [ 7] include Letters in word characters |
90a59240 |
635 | [ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings |
776f8809 |
636 | [ 9] see UTR#13 Unicode Newline Guidelines |
637 | [10] should do ^ and $ also on \x{2028} and \x{2029} |
638 | |
639 | =item * |
640 | |
641 | Level 2 - Extended Unicode Support |
642 | |
643 | 3.1 Surrogates - MISSING |
644 | 3.2 Canonical Equivalents - MISSING [11][12] |
645 | 3.3 Locale-Independent Graphemes - MISSING [13] |
646 | 3.4 Locale-Independent Words - MISSING [14] |
647 | 3.5 Locale-Independent Loose Matches - MISSING [15] |
648 | |
649 | [11] see UTR#15 Unicode Normalization |
650 | [12] have Unicode::Normalize but not integrated to regexes |
651 | [13] have \X but at this level . should equal that |
652 | [14] need three classes, not just \w and \W |
653 | [15] see UTR#21 Case Mappings |
654 | |
655 | =item * |
656 | |
657 | Level 3 - Locale-Sensitive Support |
658 | |
659 | 4.1 Locale-Dependent Categories - MISSING |
660 | 4.2 Locale-Dependent Graphemes - MISSING [16][17] |
661 | 4.3 Locale-Dependent Words - MISSING |
662 | 4.4 Locale-Dependent Loose Matches - MISSING |
663 | 4.5 Locale-Dependent Ranges - MISSING |
664 | |
665 | [16] see UTR#10 Unicode Collation Algorithms |
666 | [17] have Unicode::Collate but not integrated to regexes |
667 | |
668 | =back |
669 | |
c349b1b9 |
670 | =head2 Unicode Encodings |
671 | |
672 | Unicode characters are assigned to I<code points> which are abstract |
86bbd6d1 |
673 | numbers. To use these numbers various encodings are needed. |
c349b1b9 |
674 | |
675 | =over 4 |
676 | |
677 | =item UTF-8 |
678 | |
86bbd6d1 |
679 | UTF-8 is the encoding used internally by Perl. UTF-8 is a variable |
c349b1b9 |
680 | length (1 to 6 bytes, current character allocations require 4 bytes), |
86bbd6d1 |
681 | byteorder independent encoding. For ASCII, UTF-8 is transparent |
682 | (and we really do mean 7-bit ASCII, not any 8-bit encoding). |
c349b1b9 |
683 | |
684 | =item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks) |
685 | |
686 | UTF-16 is a 2 or 4 byte encoding. The Unicode code points |
687 | 0x0000..0xFFFF are stored in two 16-bit units, and the code points |
688 | 0x010000..0x10FFFF in four 16-bit units. The latter case is |
689 | using I<surrogates>, the first 16-bit unit being the I<high |
690 | surrogate>, and the second being the I<low surrogate>. |
691 | |
692 | Surrogates are code points set aside to encode the 0x01000..0x10FFFF |
693 | range of Unicode code points in pairs of 16-bit units. The I<high |
694 | surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates> |
695 | are the range 0xDC00..0xDFFFF. The surrogate encoding is |
696 | |
697 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
698 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
699 | |
700 | and the decoding is |
701 | |
702 | $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00); |
703 | |
86bbd6d1 |
704 | Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16 |
c349b1b9 |
705 | itself can be used for in-memory computations, but if storage or |
86bbd6d1 |
706 | transfer is required, either UTF-16BE (Big Endian) or UTF-16LE |
c349b1b9 |
707 | (Little Endian) must be chosen. |
708 | |
709 | This introduces another problem: what if you just know that your data |
710 | is UTF-16, but you don't know which endianness? Byte Order Marks |
711 | (BOMs) are a solution to this. A special character has been reserved |
86bbd6d1 |
712 | in Unicode to function as a byte order marker: the character with the |
713 | code point 0xFEFF is the BOM. |
042da322 |
714 | |
c349b1b9 |
715 | The trick is that if you read a BOM, you will know the byte order, |
716 | since if it was written on a big endian platform, you will read the |
86bbd6d1 |
717 | bytes 0xFE 0xFF, but if it was written on a little endian platform, |
718 | you will read the bytes 0xFF 0xFE. (And if the originating platform |
719 | was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.) |
042da322 |
720 | |
86bbd6d1 |
721 | The way this trick works is that the character with the code point |
722 | 0xFFFE is guaranteed not to be a valid Unicode character, so the |
723 | sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in |
042da322 |
724 | little-endian format" and cannot be "0xFFFE, represented in big-endian |
725 | format". |
c349b1b9 |
726 | |
727 | =item UTF-32, UTF-32BE, UTF32-LE |
728 | |
729 | The UTF-32 family is pretty much like the UTF-16 family, expect that |
042da322 |
730 | the units are 32-bit, and therefore the surrogate scheme is not |
731 | needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and |
732 | 0xFF 0xFE 0x00 0x00 for LE. |
c349b1b9 |
733 | |
734 | =item UCS-2, UCS-4 |
735 | |
86bbd6d1 |
736 | Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit |
737 | encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2 |
738 | is not extensible beyond 0xFFFF, because it does not use surrogates. |
c349b1b9 |
739 | |
740 | =item UTF-7 |
741 | |
742 | A seven-bit safe (non-eight-bit) encoding, useful if the |
743 | transport/storage is not eight-bit safe. Defined by RFC 2152. |
744 | |
745 | =head2 Unicode in Perl on EBCDIC |
746 | |
747 | The way Unicode is handled on EBCDIC platforms is still rather |
86bbd6d1 |
748 | experimental. On such a platform, references to UTF-8 encoding in this |
c349b1b9 |
749 | document and elsewhere should be read as meaning UTF-EBCDIC as |
750 | specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues |
751 | are specifically discussed. There is no C<utfebcdic> pragma or |
86bbd6d1 |
752 | ":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean |
753 | the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> |
754 | for more discussion of the issues. |
c349b1b9 |
755 | |
756 | =back |
757 | |
393fec97 |
758 | =head1 SEE ALSO |
759 | |
c349b1b9 |
760 | L<encoding>, L<Encode>, L<open>, L<bytes>, L<utf8>, L<perlretut>, |
761 | L<perlvar/"${^WIDE_SYSTEM_CALLS}"> |
393fec97 |
762 | |
763 | =cut |