W3C home > Mailing lists > Public > www-svg@w3.org > April 1999

Problems with SVG's CSS properties

From: Ian Hickson <py8ieh@bath.ac.uk>
Date: Thu, 22 Apr 1999 04:01:17 +0100 (BST)
To: SVG <www-svg@w3.org>
Message-ID: <Pine.GSO.4.04.9904220339310.19505-100000@amos.bath.ac.uk>

There are a few problems with SVG and its use of CSS properties.


'text-transform'
================

This property is now defined in both SVG and CSS2. In CSS2 it is used
for changing the case of text, in SVG it is a text analogue of the
'transform' property. The SVG working group may wish to consider
renaming the SVG 'text-transform' property, since the CSS property may
be of use in SVG as well.


'font' shorthand property
=========================

Because SVG uses different conventions for <length>, in particular
because it allows unit-less numbers, the CSS2 'font' shorthand
property will be unparsable in SVG. For example, how should the
following be handled?

   #heavy { font: 900 large sans-serif; }

According to the CSS specification, the '900' keyword will be parsed
as the 'font-weight' value, the 'large' keyword will be parsed as the
'font-size' value, the 'sans-serif' keyword will be parsed as the
'font-family' value, and all other font properties will be set to
their initial values.

However, in SVG '900' is a valid font-size, and so the above rule is
ambiguous: as well as the interpretation above, another, equally valid
interpretation is that '900' is the 'font-size' (900 user units), and
'large sans-serif' is the 'font-family'.

Two possible solutions are to either not use the 'font' shorthand
property in SVG, or to give user units a unit specifier such as 'uu'.


'text-direction'
================

There appears to be overlap between the SVG 'text-direction' property
and the CSS2 'direction' property. The SVG working group may wish to
use the name 'direction' instead of 'text-direction', and then extend
the allowed values in SVG.


text formatting
===============

The current spec states that:

# The standard set of text and font properties from CSS2 apply,
# including 'text-align' and 'vertical-align'.

How is 'vertical-align' to be applied? In CSS, 'vertical-align' has a
pivotal role in the inline level formatting model. Will SVG use the
entire CSS inline level formatting model? This seems like serious
overkill since SVG uses a much more direct approach to layout (namely,
giving x and y coordinates).

Exactly which font text and font properties will SVG borrow from CSS2? 

For example, will any of the following be used?

   text-decoration 
   text-shadow
   text-indent
   font-size-adjust
   
Note that if 'text-decoration' is used, then it will have to be
defined much more precisely than in CSS if results are to be reliably
reproduced across implementations.


-- 
Ian Hickson 
U+2642 U+2651
U+262E U+2603 U+263A
Received on Wednesday, 21 April 1999 23:01:20 GMT

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