W3C home > Mailing lists > Public > www-svg@w3.org > November 2004

Re: CSS style sheets in SVG enable high and low contrast

From: Jonathan Chetwynd <j.chetwynd@btinternet.com>
Date: Mon, 29 Nov 2004 15:51:57 +0000
Message-Id: <9987A006-421E-11D9-86AF-000A95C7D298@btinternet.com>
Cc: <www-svg@w3.org>
To: "Jim Ley" <jim@jibbering.com>


"it can't be done by the user"
What can your reason be for asserting this? it's not as easy as 
asserting black background, but with good authoring tools it is 
possible. In particular the example given demonstrates how, for the 
simple example of 'border' the user could.
authors need to understand how to enable users to make choices for 
themselves. Style sheets provide an appropriate mediation.
However this does rely on conscientious authors making that step.

This is particularly relevant to mobile phone users, who have very 
limited screen size, which is almost certain not to change.
many users will benefit from a sophisticated contrast control. It seems 
almost impossible that this wont arrive promptly.
Style sheets are the clearly obvious and currently available solution. 
Whatever eventual solution is adopted the user will effectively create 
a description of their preferred style, and compliant authors will 
supply data that fits this requirement's sheet, and does so in an 
excellent and appropriate fashion.

As I originally asked, if you have examples that demonstrate how users 
can choose high or low contrast, please let's see them.
alternatively, some other accessibility style solution would be great*.
Hypothetical future realities are much harder to determine.


Jonathan Chetwynd
http://www.peepo.co.uk     "It's easy to use"

* "link to another version of the page"
A good reason for keeping it all in a single document, is ease of 
maintenance. I'm surprised you mention this, as it's a regular WCAG 
issue. Furthermore, by understanding the design issues and 
incorporating them into a single document, one makes small coherent 
steps towards graphical accessibility, whereas creating alternatives 
merely leaves the understanding disparate.

On 29 Nov 2004, at 14:50, Jim Ley wrote:

"Jonathan Chetwynd" <j.chetwynd@btinternet.com>
> I dont agree at all, the style sheets referred to can be applied by 
> the user, they could more usefully be applied across a greater variety 
> of sites if another semantic layer were available that more fully 
> described GUIs.

You cannot change the colour of graphical elements unless you _know_ 
that the colour isn't relevant (consider the key to a simple graph, you 
need the polyline and the text both to remain the same colour, this 
isn't possible in CSS)  If we develop some description language that 
can define these sort of elements, then that would as you say be a 
great benefit, however it would not be usable with user CSS stylesheets 
alone.  So even with this advance that doesn't exist, or even being 
worked on, user stylesheets wouldn't help any.

User stylesheets as a repair for specific SVG sites, perhaps that's 
useful, but it's an incredibly expensive activity, and applies to such 
a small number of cases and is achievable by using DOM methods to 
inject styles.

> afaik the common user agents do support stylesheets, it is the 
> changing of stylesheets that remains problematical.

Which means they only support a subset, and especially once you move to 
the mobile focussed UA's there's nothing more than style="..." as an 
alternative to attributes (why they did that I don't know, I 
particularly dislike this deliberate partial implementation of 
specifications, but I can understand the motivation.

> Please provide any evidence that supports your statement: "the exact 
> same can be achieved in other ways"

at it's simplest, simply link to another version of the page, there's 
no reason to have all that mess - like we discussed on #svg with the 
systemLanguage detection (with Vincent), there's actually little reason 
to do all the changes in a single document, alterernate representations 
make a lot of sense, a lack of reliance on javascript is certainly one 
well worth considering.

It is also possible using SMIL animation, again which avoids script, 
with its attendant advantages, but instead requires SMIL, or if you 
wish you can use other javascript.

none of it's interesting though, it's all simple to author, and has to 
be done by the author, it can't be done by the user.  In the case of 
contrast there is research into automated methods to achieve it, 
however as you've noted they're not very good, they're also not 
achievable with CSS user stylesheets, so will need a new Access 
Technology (I believe some of it can be achieved with filters, but am 
waiting on hearing back from some accessibility people I've asked.) - 
if it can a bookmarklet could do it in ASV+IE, or MozSVG when it gets 

> Please note that WAI have recently also published draft documents, but 
> they dont refer to SVG.

Even I know of work on the SVG Accessibility document, it's as mature 
as the scripting one, which is currently too simplistic to really be 

Received on Monday, 29 November 2004 15:52:30 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 8 March 2017 09:47:01 UTC