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Re: [json] JSON strings cannot point to post-BMP Unicode codepoints?

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  • David Heiko Kolf
    ... Yes, you can put post-BMP codepoints directly as part of the string literals. If there are control characters outside of the BMP in your text they could
    Message 1 of 8 , Apr 7, 2013
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      Shriramana Sharma wrote:
      > http://en.wikipedia.org/wiki/JSON says: "The default character
      > encoding for JSON is UTF8; it also supports UTF16 and UTF32." but I'm
      > not sure about it because it is not mentioned explicitly on the
      > json.org page and it is also not very clear to me as to what exactly
      > that statement means. Does it mean that even though there is no \U
      > notation, I can directly input post-BMP codepoints as part of the
      > string literals? The json.org page does say "any-Unicode-character".
      > In this case even the \u notation is only there as a just-in-case?
      > (Even if so, why not \U too just-in-case?)

      Yes, you can put post-BMP codepoints directly as part of the string
      literals. If there are control characters outside of the BMP in your
      text they could still be encoded as surrogate pairs. This isn't the
      decision of JSON -- JavaScript uses UTF16 internally for all strings.

      Best Regards,

      David Kolf
    • John Cowan
      ... It can be represented either as the actual character, 4 bytes in any of UTF-8, UTF-16, or UTF-32; or else as two consecutive ASCII escapes: uD804 uDC05 .
      Message 2 of 8 , Apr 7, 2013
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        Shriramana Sharma scripsit:

        > However, if that restriction of *four* hex digits is meant to be
        > enforced, then it means that post-BMP codepoints (such as 0x11005
        > BRAHMI LETTER A) cannot be represented in such strings directly, but
        > that they have to be manually (i.e. by the program outputting JSON-ed
        > data) decomposed into their equivalent UTF16 surrogate pairs (for
        > instance, 0xd804 0xdc05).

        It can be represented either as the actual character, 4 bytes in any
        of UTF-8, UTF-16, or UTF-32; or else as two consecutive ASCII escapes:
        "\uD804\uDC05".

        > IMHO this is an unnecessary restriction.

        JSON is backward compatible by design with ECMAScript 3, which does not
        support the \U escape.

        > Does it mean that even though there is no \U notation, I can directly
        > input post-BMP codepoints as part of the string literals?

        Correct.

        > In this case even the \u notation is only there as a just-in-case?

        Just so.

        --
        There are three kinds of people in the world: John Cowan
        those who can count, cowan@...
        and those who can't.
      • douglascrockford
        JavaScript, Java, and many other languages, were developed at a time when Unicode was going to be a 16-bit character set. Unicode later grew into a 21-bit
        Message 3 of 8 , Apr 7, 2013
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          JavaScript, Java, and many other languages, were developed at a time when Unicode was going to be a 16-bit character set. Unicode later grew into a 21-bit character set.

          JSON took its representation of strings from JavaScript.
        • Dennis Gearon
          There s some contradiction in the json RFC. If the encoding shall be Unicode and default is UTF-8 as is stated, then ALL normal planes, including those
          Message 4 of 8 , Apr 7, 2013
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            There's some contradiction in the json RFC. If the encoding 'shall be Unicode'
            and default is UTF-8 as is stated, then ALL normal planes, including those
            outside of the BMP can be encoded w/o any special escaping (excluding the
            special set chars escaped for JSON). UTF16 doesn't apply, right?

            See http://en.wikipedia.org/wiki/Plane_%28Unicode%29, where it says it is NOT a
            UTF-8 limit, being inside the BMP, but UTF16. It goes further to say that with
            ONLY 4 bytes, utf-8 can represent twice as many code points as UTF16 using
            surrogate pairs.


            If I have read everything correctly.

            Dennis Gearon


            Never, ever approach a computer saying or even thinking "I will just do this
            quickly."




            ________________________________
            From: douglascrockford <douglas@...>
            To: json@yahoogroups.com
            Sent: Sun, April 7, 2013 11:30:30 AM
            Subject: [json] Re: JSON strings cannot point to post-BMP Unicode codepoints?


            JavaScript, Java, and many other languages, were developed at a time when
            Unicode was going to be a 16-bit character set. Unicode later grew into a 21-bit
            character set.


            JSON took its representation of strings from JavaScript.




            [Non-text portions of this message have been removed]
          • John Cowan
            ... That s right. However, escapes are handy for representing stray Unicode characters that aren t easy to type, just as in HTML or XML. Unlike those
            Message 5 of 8 , Apr 8, 2013
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              Dennis Gearon scripsit:

              > There's some contradiction in the json RFC. If the encoding 'shall be
              > Unicode' and default is UTF-8 as is stated, then ALL normal planes,
              > including those outside of the BMP can be encoded w/o any special
              > escaping (excluding the special set chars escaped for JSON).

              That's right. However, escapes are handy for representing stray Unicode
              characters that aren't easy to type, just as in HTML or XML. Unlike
              those languages, JSON requires two consecutive escapes to represent a
              non-BMP character.

              What's ambiguous is whether a JSON document like

              ["\uD800"]

              with an unpaired escaped surrogate, is valid or not. It is valid in
              JavaScript. Crockford says it was not his intention to rule it out,
              and I say it is implicitly forbidden by the definition in section 1 that
              a string is a sequence of zero or more Unicode characters, because U+D800
              is not a Unicode character.

              > UTF16 doesn't apply, right?

              UTF-16 is a perfectly cromulent encoding for JSON, though probably not
              much used.

              > See http://en.wikipedia.org/wiki/Plane_%28Unicode%29, where it says
              > it is NOT a UTF-8 limit, being inside the BMP, but UTF16. It goes
              > further to say that with ONLY 4 bytes, utf-8 can represent twice as
              > many code points as UTF16 using surrogate pairs.

              UTF-8 and UTF-16 can represent the exact same range of code points,
              namely 0-10FFFF excluding D800-DFFF. Any UTF-8 byte sequence that
              purports to represent any other code point has been illegal for a long
              time now.

              --
              We pledge allegiance to the penguin John Cowan
              and to the intellectual property regime cowan@...
              for which he stands, one world under http://www.ccil.org/~cowan
              Linux, with free music and open source
              software for all. --Julian Dibbell on Brazil, edited
            • Shriramana Sharma
              Hello people and thanks for your responses. I hope I understand correctly that compatibility with JavaScript and the ECMAScript standard dictates that it would
              Message 6 of 8 , Apr 8, 2013
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                Hello people and thanks for your responses. I hope I understand
                correctly that compatibility with JavaScript and the ECMAScript
                standard dictates that it would not be advisable for JSON to
                unilaterally add the extension of \U, but since any valid Unicode
                characters can be part of string literals (encoded in the appropriate
                encoding) I guess this is not too much of a problem. Thank you.
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