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