Char encoding and subsets

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  • Ian Rastall
    #1

    Char encoding and subsets

    This is my understanding so far, and please correct any errors:

    1. US-ASCII is a subset of ISO-8859-1
    2. US-ASCII is a subset of UTF-8
    3. ISO-8859-1 is not a subset of UTF-8

    But ... are the numeric entities (in hex or decimal) for ISO-8859-1
    the same in UTF-8?

    Can an HTML document that uses only Latin-1 numeric entities have
    its content-type changed to UTF-8 and still be valid?

    Do Latin-1 numeric entities have to be written either as x## or ###,
    or can they have trailing zeros, like x00## or 0###, which is what
    you would have with UTF-8?

    TIA

    Ian
    --
    http://www.aspipes.org/

    http://www.bookstacks.org/

    http://www.learnsomethingnew.us/

    Tags: None
    • Andreas Prilop
      #2
      Re: Char encoding and subsets

      Ian Rastall <idrastall@sbcg lobal.net> wrote:
      [color=blue]
      > 3. ISO-8859-1 is not a subset of UTF-8[/color]

      Since "subset" could only refer to character _sets_ but not encodings,
      your statement is meaningless.
      [color=blue]
      > But ... are the numeric entities (in hex or decimal) for ISO-8859-1
      > the same in UTF-8?[/color]

      There are entities like &#ouml; and numeric character references
      like &#246; . The number (246) refers to Unicode and it happens to be
      the same code position in ISO-8859-1 whenever number < 256. (That
      includes the range 128...159, which are no graphic characters.)
      <http://www.w3.org/TR/html4/charset.html#h-5.3.1>
      [color=blue]
      > Can an HTML document that uses only Latin-1 numeric entities have
      > its content-type changed to UTF-8 and still be valid?[/color]

      Yes - if you mean "numeric character references" and Content-type
      "text/html;charset=UT F-8".
      [color=blue]
      > Do Latin-1 numeric entities have to be written either as x## or ###,
      > or can they have trailing zeros, like x00## or 0###,[/color]

      What's the point in writing &#0246; ?
      [color=blue]
      > which is what you would have with UTF-8?[/color]

      No, we wouldn't.

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        • Ian Rastall
          #3
          Re: Char encoding and subsets

          Thanks, man. I knew what to expect, so I got a smile out of it. But
          that link will come in very handy, and I did get my questions
          answered.

          Ian
          --
          http://www.aspipes.org/

          http://www.bookstacks.org/

          http://www.learnsomethingnew.us/

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