- From: Jukka K. Korpela <jkorpela@cs.tut.fi>
- Date: Thu, 23 Feb 2006 17:35:02 +0200 (EET)
- To: CSS validator list <www-validator-css@w3.org>
On Thu, 23 Feb 2006, olivier Thereaux wrote: > On 21 Feb 2006, at 21:07, Jukka K. Korpela wrote: >> >> Anyway, the FAQ entry >> http://www.websitedev.de/css/validator-faq#color >> explains the issue, though rather compactly: >> "If you don't specify color and background-color at the same level of >> specifity, your style sheet might clash with user style sheets." >> Besides, it's not the whole truth. > > The FAQ could probably be updated to > - mention in more details the fact that the warning is not one of conformance > to CSS, but one of accessibility. Labeling it as "accessibility" wouldn't be quite adequate. If the checker warned, say, about too small contrast between background and text color, _that_ would be about accessibility. The risk of _arbitrary_ combination of background and text color is about robustness. If the colors are, for example, exactly the same, you don't need to be visually impaired to miss information. > - stress the fact that it is a suggestion, not an error (somebody today told > me that it would make fewer people ill at ease if the wording was less harsh) Actually the wording _should_ be stronger, as we can deduce from the protests against the warning - regularly reflecting lack of understanding the issue, even after explanations. It's called a warning, and that should suffice, unless you wish to make it _strong_ warning. The _heading_ of the explanation is somewhat misleading, however. It contributes to the common misconception about a "nagging" "validator" when it uses the verb "complain". The verb "warn" would be more adequate. Of course, giving the checker a more adequate name, instead of misrepresenting it as a validator, would help in general. But it seems that such an action will not be taken. > - mention that the problem could be caused by cascading, maybe give a short > example Just mentioning cascading would not help much, since most author keep misunderstanding how the cascade works. > Anyone interested in drafting a wording for > the extended section? Since the warning is so commonly misunderstood (and therefore criticized), even after attempts at helpful explanations, I'm afraid there is no simple and short explanation that would suffice. START PROPOSED TEXT If you assign a value to the color property without simultaneously assigning a value to the background-color property, unreadable or otherwise undesired color combinations may appear. The reason is that your style sheet may be applied together with a user style sheet (or a browser style sheet, or another author style sheet). Even if the other style sheet is well-designed, CSS principles may imply that the color is taken from one style sheet and the background-color from another. This may result in black text on black background, for example. Specifying background-color: transparent is not sufficient for avoiding the problem. Consider the following example: body { background: white; color: black; } h1 { color: #060; background: transparent; } Assuming that h1 appears as a subelement of body, this results in h1 displayed in color #060 (dark green) on white background, which is the background of body shining through. However, if a user style sheet contains body { background: #060 !important; color: white !important; } then the background of body that shines through will be #060, making the heading text completely invisible. Thus, it is normally best to rewrite the style sheet so that background colors are set explicitly, even though this causes some inconvenience. In rare cases, it might be possible to analyze reliably that the risk described here does not exist or that it is worth taking. Technically, this message is a warning, not an error message, since taking the risk does not violate any requirement in CSS specifications. END PROPOSED TEXT This could be followed by a paragraph containing the second half of the current explanation, reworded e.g. as "For more information, consult Section 9.1 "Color Contrast" in the W3C Note "CSS Techniques for Web Content Accessibility Guidelines 1.0" or the article CSS Color Issues by the CSS Pointers Group for a discussion." -- Jukka "Yucca" Korpela, http://www.cs.tut.fi/~jkorpela/
Received on Thursday, 23 February 2006 15:35:16 UTC