RE: Coloured diacritics (Was: Transcoding Tamil in the presence of markup)

From: Philippe Verdy (verdy_p@wanadoo.fr)
Date: Mon Dec 08 2003 - 20:11:24 EST

  • Next message: Chris Jacobs: "Re: Coloured diacritics (Was: Transcoding Tamil in the presence of markup)"

    Peter Constable writes:
    > > A very tentative suggestion for some glue: a character which can take
    > > combining marks but whose function is to throw those marks back on to
    > > the preceding base character, preceding any markup.
    >
    > I see no particular value in this. The font rendering of <span>base
    > diacritic</span> should be exactly the same as that for
    > <span>base</span><span>diacritic</span> provided the font
    > characteristics are the same or do not affect metrics.

    This is wrong here: there's no guarantee offered by HTML that:
            <span>base</span><span>diacritic</span>
    MUST render the same as:
            <span>base diacritic</span>
    simply because the former is two instances of the span element,
    which _by default_ has a "inline" layout, but may be given in a
    stylesheet another layout such as "block"; in that case it would
    render the same as if it was:
            <span>base<br/>diacritic</span>

    You can't "simplify" an XML or SGML document before first applying
    the style information defined either by an explicit stylsheet
    somewhre in the document, or externally with a XML/HTML processing
    engine, or by user settings, and then only by default rendering rules
    defined by the HTML schema for the <span> element.

    As the HTML renderer does not work directly on the XML parsed tree,
    but on the augmented tree where style elements have been applied to
    create the document layout. In HTML the complete tree that is
    rendered contains one node per character and per style/layout node,
    and then the tree is simplified for actual rendering by fonts, if
    this saves works in fonts and optimizes the graphic rendering pass.

    But it is in fact much more complex than what it looks, as fonts are
    prividing information to the HTML layout engine, so that it can compute
    widths and heights, and where to apply line breaks, and if needed it
    will transform the tree while parsing it with font metrics information
    to reflect the final layout that will be finally positioned and drawn
    with fonts.

    See the reference model for composition in HTML with CSS or XSLT where
    the layout plays a huge role on the rendering. It has nothing to do
    with considerations on the source markup used to build the first parsing
    tree, or with the styling pass that transforms the source elements into
    layout elements...

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