diff options
Diffstat (limited to 'pod/perluniintro.pod')
| -rw-r--r-- | pod/perluniintro.pod | 49 |
1 files changed, 32 insertions, 17 deletions
diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod index 3fbff0024f..37bab49308 100644 --- a/pod/perluniintro.pod +++ b/pod/perluniintro.pod @@ -93,25 +93,40 @@ character. Firstly, there are unallocated code points within otherwise used blocks. Secondly, there are special Unicode control characters that do not represent true characters. -A common myth about Unicode is that it is "16-bit", that is, -Unicode is only represented as C<0x10000> (or 65536) characters from -C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July +When Unicode was first conceived, it was thought that all the world's +characters could be represented using a 16-bit word; that is a maximum of +C<0x10000> (or 65536) characters from C<0x0000> to C<0xFFFF> would be +needed. This soon proved to be false, and since Unicode 2.0 (July 1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>), -and since Unicode 3.1 (March 2001), characters have been defined -beyond C<0xFFFF>. The first C<0x10000> characters are called the -I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode -3.1, 17 (yes, seventeen) planes in all were defined--but they are -nowhere near full of defined characters, yet. - -Another myth is about Unicode blocks--that they have something to -do with languages--that each block would define the characters used -by a language or a set of languages. B<This is also untrue.> +and Unicode 3.1 (March 2001) defined the first characters above C<0xFFFF>. +The first C<0x10000> characters are called the I<Plane 0>, or the +I<Basic Multilingual Plane> (BMP). With Unicode 3.1, 17 (yes, +seventeen) planes in all were defined--but they are nowhere near full of +defined characters, yet. + +When a new language is being encoded, Unicode generally will choose a +C<block> of consecutive unallocated code points for its characters. So +far, the number of code points in these blocks has always been evenly +divisible by 16. Extras in a block, not currently needed, are left +unallocated, for future growth. But there have been occasions when +a later relase needed more code points than available extras, and a new +block had to allocated somewhere else, not contiguous to the initial one +to handle the overflow. Thus, it became apparent early on that "block" +wasn't an adequate organizing principal, and so the C<script> property +was created. Those code points that are in overflow blocks can still +have the same script as the original ones. The script concept fits more +closely with natural language: there is C<Latin> script, C<Greek> +script, and so on; and there are several artificial scripts, like +C<Common> for characters that are used in multiple scripts, such as +mathematical symbols. Scripts usually span varied parts of several +blocks. For more information about scripts, see L<perlunicode/Scripts>. The division into blocks exists, but it is almost completely -accidental--an artifact of how the characters have been and -still are allocated. Instead, there is a concept called I<scripts>, which is -more useful: there is C<Latin> script, C<Greek> script, and so on. Scripts -usually span varied parts of several blocks. For more information about -scripts, see L<perlunicode/Scripts>. +accidental--an artifact of how the characters have been and still are +allocated. (Note that this paragraph has oversimplified things for the +sake of this being an introduction. Unicode doesn't really encode +languages, but the writing systems for them--their scripts; and one +script can be used by many languages. Unicode also encodes things that +aren't really about languages, such as symbols like C<BAGGAGE CLAIM>.) The Unicode code points are just abstract numbers. To input and output these abstract numbers, the numbers must be I<encoded> or |