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Re: An Accessible method of hiding HTML content


From: Paul Bohman
Date: Jun 5, 2004 1:54PM

Derek wrote:

> This point is really at the crux of the issue. We regularly teach developers
> that when they are building their CSS rules that they ensure they declare
> backgrounds (either images, or colours) with an appropriate foreground so
> that if images are off, or stylesheets are off, or in some other situation,
> there is appropriate contrast between foreground and background. The W3C's
> CSS Validator even flags this issue as a warning.

My response:

What you have described is good advice in a general sense. However, when
users are granted the ability to change the color of both text and
background, the end result is that you, the designer, have no control
over what your Web page is going to look like. Users with low vision
frequently set dark background colors and light text colors, which,
despite all of your careful planning, make graphics and other parts of
the page difficult to discern, especially if your Web page did not have
a dark background to begin with. Users can even set orange text against
a yellow background if they want to, though I doubt anyone would do this
for accessibility reasons.

Rather than lament this lack of control, it must simply be accepted, and
in many ways embraced. User freedom and personalization is an important
concept in the accessibility world that people with disabilities have
been crying out for. They now have this freedom (or at least large parts
of this freedom--there is still room for growth here), and it should be

Users can turn off images, they can change the font style, they can
linearize text, they can apply their own style sheets, they can convert
it into other formats... In short, they can "ruin" your design in every
way imaginable.

Derek asked:

> 1. What mechanisms are these low vision users using to override the styles?
> Browser settings? User Style Sheets? Other?

My response:

The most common and easiest method is to go into the settings of the
browser and override the color settings for text and background. You can
do this in IE, Netscape, Opera, and others. Every browser does this
somewhat differently, but most turn off background images in addition to
the background colors.

There are more sophisticated methods. You can design your own
stylesheet, or download them, but I doubt many users actually do
this--even among those with disabilities.

The implication is that nothing of importance should go in background

Derek also asked:

> 2. Where are they learning how to do so? On their own? From tutors? From
> online resources?

My response:

I don't know the full answer to this question, but I do know that some
assistive technologies, including some screen readers and screen
enlargers allow users to change the background settings quite easily.

Another question by Derek:

> 3. Can we realistically expect the users or those teaching them to override
> styles to do so in a way to ensure that both foreground and background are
> overridden so there is no conflict as you suggest?

My response:

Sort of. You can tell people to create both a custom background color
and text color that are accessible in contrast to one another. Most
people do this already, and don't really need to be told to do it.

That's not really the problem. The problem is that the browsers allow
users to easily override *parts* of the author's style sheet, but the
browser doesn't tell you that that's what's happening. It just asks you,
for example, if you want to specify a certain background color and text

That's a good option to have, but it's an incomplete set of options. In
many cases, just overriding the font and background color produces
results that are not optimally accessible, partly due to the fact that
these settings also get rid of background images.

What can authors do about this? Not much. The user is making the
decision to change the page styles, and the browser is allowing this

In many cases, the best option for people who need custom styles is to
turn off the *entire* style sheet and replace it with their own (e.g.
black background, yellow enlarged text). Because this gives them *all*
of the text and images, and there is no question that they are getting
all of the content.

Unfortunately, it's not quite that simple for all circumstances. If the
style sheets provide visual contextual, orientation or organization
cues, then these cues will be lost (as I've explained before), so on
some Web pages, users are better off retaining parts of the style sheet,
such as positioning, even when colors are changed.

Those of us who train people with disabilities in using the Web ought to
inform them that there is a good chance that they will miss out on some
visual aspects of the page if they change the font and/or background
settings. That's an unfortunate fact of life, because too much of the
Web content out there depends at least partly on visual communication.

However, from the point of view of developers, we can try to ensure that
all aspects of "visual communication" in our Web content are conveyed to
users who don't have access to this visual information. When users turn
off only parts of our style sheets, that can be tricky, especially in
the context of low vision users. I admit that I don't have all of the
answers in this area in terms of low vision. Blind users are a bit
easier to accommodate in this context. By providing text-based cues (as
explained in previous posts), we can help blind users orient themselves
within the page and we can compensate for their inability to see visual

I know this is a bit of a convoluted explanation, but I hope it makes
some sense.

MY CONCLUSION (at least for now):

We, as developers, can provide cues to blind users that compensate for a
lack of visual ability. In the case of low vision users, however, their
ability to change background colors and foreground colors (and other
settings) can make content either more or less accessible to them,
depending on the settings chosen and on the nature of the content being
altered. I don't think there is a formula that works for all users or
for all Web content.

BUT, if developers create semantically correct Web sites that are truly
accessible to the blind, then people with low vision can turn off ALL of
the styles and the content will likewise be accessible to them, in the
same way that it is accessible to blind users.

Paul Bohman
Project Coordinator
WebAIM (Web Accessibility in Mind)
Utah State University

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