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RE: [XSL-FO] em

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  • Tony Graham
    ... From the XSL CR: 5.9.7.2. Relative Lengths A relative length is a unit-based value that is measured against the current value of the font-size property.
    Message 1 of 11 , May 14 6:50 AM
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      Joshua Kimmel wrote at 14 May 2001 09:38:47 -0400:
      > Additionally, I haven't found anything that says that the current use of the
      > em unit is equal to the fonts current size. CSS books still claims its use
      > as being equal to the M of the current font, and fop's support for the em
      > unit doesn't hold up to that either.

      From the XSL CR:

      5.9.7.2. Relative Lengths

      A relative length is a unit-based value that is measured against
      the current value of the font-size property.

      There is only one relative unit of measure, the "em". The
      definition of "1em" is equal to the current font size. For example,
      a value of "1.25em" is 1.25 times the current font size.

      When an em measurement is used in an expression, it is converted
      according to the font-size value of the current property's
      context. The result of the expression is an absolute length. See §
      7.7.4 font-size on page 193

      Regards,


      Tony Graham
      ------------------------------------------------------------------------
      Tony Graham mailto:tony.graham@...
      Sun Microsystems Ireland Ltd Phone: +353 1 8199708
      Hamilton House, East Point Business Park, Dublin 3 x(70)19708
    • Joshua Kimmel
      Hey, now that s some good information. Thank you for pointing it out to me. Josh ... From: Tony Graham [mailto:Tony.Graham@ireland.sun.com] Sent: Monday, May
      Message 2 of 11 , May 14 6:56 AM
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        Hey, now that's some good information. Thank you for pointing it out to me.

        Josh

        -----Original Message-----
        From: Tony Graham [mailto:Tony.Graham@...]
        Sent: Monday, May 14, 2001 9:51 AM
        To: XSL-FO@yahoogroups.com
        Subject: RE: [XSL-FO] em


        Joshua Kimmel wrote at 14 May 2001 09:38:47 -0400:
        > Additionally, I haven't found anything that says that the current use of
        the
        > em unit is equal to the fonts current size. CSS books still claims its
        use
        > as being equal to the M of the current font, and fop's support for the em
        > unit doesn't hold up to that either.

        >From the XSL CR:

        5.9.7.2. Relative Lengths

        A relative length is a unit-based value that is measured against
        the current value of the font-size property.

        There is only one relative unit of measure, the "em". The
        definition of "1em" is equal to the current font size. For example,
        a value of "1.25em" is 1.25 times the current font size.

        When an em measurement is used in an expression, it is converted
        according to the font-size value of the current property's
        context. The result of the expression is an absolute length. See §
        7.7.4 font-size on page 193

        Regards,


        Tony Graham
        ------------------------------------------------------------------------
        Tony Graham mailto:tony.graham@...
        Sun Microsystems Ireland Ltd Phone: +353 1 8199708
        Hamilton House, East Point Business Park, Dublin 3 x(70)19708

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      • Christopher R. Maden
        ... An em-spec d measurement can t change *while viewing* a PDF, because the font size can t change. When formatting a document
        Message 3 of 11 , May 14 7:00 AM
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          At 06:38 14-05-2001, Joshua Kimmel wrote:
          >If that's true about using the em, that it doesn't change based on the font
          >sizes with in my fo document, then that's cool.

          <confusion amount="more"/>

          An em-spec'd measurement can't change *while viewing* a PDF, because the
          font size can't change. When formatting a document using XSL, 1 em will
          always be the current font size. It won't *change* as such, over time, but
          1 em will mean different lengths in different FOs, depending on the font
          size in use for that FO.

          >My old method was to measure the width of the "M" in whatever font manually,
          >then code it in as a variable, and then just multiply by it wherever I
          >needed to maintain a size of say exactly 60 characters in the specified
          >font.

          Ah. An average character width, unless you're using a fixed-pitch
          typeface, is not going to be 1 em. It will vary based on the face itself;
          a good way to take the measure is to type out the lowercase alphabet in
          that face and measure it.

          >Additionally, I haven't found anything that says that the current use of the
          >em unit is equal to the fonts current size.

          I believe Tony's quote from the spec fulfilled that. Out of curiousity:
          where were you looking?

          >CSS books still claims its use
          >as being equal to the M of the current font, and fop's support for the em
          >unit doesn't hold up to that either.

          Section 4.3.2 of CSS 2 says "em: the 'font-size' of the relevant font";
          section 6.1 of CSS 1 says much the same. If books about CSS disagree with
          the spec, they're wrong. In any case, we're dealing with XSL, which
          addresses a slightly different domain from CSS, and expectations based on
          CSS may prove misleading.

          -Chris
          --
          Christopher R. Maden, XML Consultant
          DTDs/schemas - conversion - ebooks - publishing - Web - B2B - training
          <URL: http://crism.maden.org/consulting/ >
          PGP Fingerprint: BBA6 4085 DED0 E176 D6D4 5DFC AC52 F825 AFEC 58DA
        • Joshua Kimmel
          I appreciate the information I ve been given. I believe I have been schooled effectively. :) 1st lesson learned. Read spec more carefully. 2nd lesson.
          Message 4 of 11 , May 14 7:15 AM
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            I appreciate the information I've been given. I believe I have been
            "schooled" effectively. :)

            1st lesson learned. Read spec more carefully.
            2nd lesson. Don't trust all CSS information to be mostly true in FO.
            3rd lesson. read better books.

            Now that I feel I have a better understanding of the em in the FO realm, has
            anybody used it in FOP?

            I mean, if I'm using it to determine a column width, and I have multiple
            fonts and sizes within my document, how do I code so a specific font is
            within the scope of that column width?

            Josh


            At 06:38 14-05-2001, Joshua Kimmel wrote:
            >If that's true about using the em, that it doesn't change based on the font
            >sizes with in my fo document, then that's cool.

            <confusion amount="more"/>

            An em-spec'd measurement can't change *while viewing* a PDF, because the
            font size can't change. When formatting a document using XSL, 1 em will
            always be the current font size. It won't *change* as such, over time, but
            1 em will mean different lengths in different FOs, depending on the font
            size in use for that FO.

            >My old method was to measure the width of the "M" in whatever font
            manually,
            >then code it in as a variable, and then just multiply by it wherever I
            >needed to maintain a size of say exactly 60 characters in the specified
            >font.

            Ah. An average character width, unless you're using a fixed-pitch
            typeface, is not going to be 1 em. It will vary based on the face itself;
            a good way to take the measure is to type out the lowercase alphabet in
            that face and measure it.

            >Additionally, I haven't found anything that says that the current use of
            the
            >em unit is equal to the fonts current size.

            I believe Tony's quote from the spec fulfilled that. Out of curiousity:
            where were you looking?

            >CSS books still claims its use
            >as being equal to the M of the current font, and fop's support for the em
            >unit doesn't hold up to that either.

            Section 4.3.2 of CSS 2 says "em: the 'font-size' of the relevant font";
            section 6.1 of CSS 1 says much the same. If books about CSS disagree with
            the spec, they're wrong. In any case, we're dealing with XSL, which
            addresses a slightly different domain from CSS, and expectations based on
            CSS may prove misleading.

            -Chris
            --
            Christopher R. Maden, XML Consultant
            DTDs/schemas - conversion - ebooks - publishing - Web - B2B - training
            <URL: http://crism.maden.org/consulting/ >
            PGP Fingerprint: BBA6 4085 DED0 E176 D6D4 5DFC AC52 F825 AFEC 58DA


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