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RE: [XSL-FO] em

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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 1 of 11 , May 14, 2001
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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 2 of 11 , May 14, 2001
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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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