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The one bug the Omni Group must not fix

November 18, 2002

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If you’re looking at this page in OmniWeb, it should look horrible. The text should be magenta on a hideous yellow-green background, and the other parts of the page should be similarly vile. For everyone else, it should look like a familiar MacEdition page, with readable black text on a white background, and the familiar dark teal and black backgrounds around the content and the ochre-ish sidebar.

How did I do this? It wasn’t browser sniffing or JavaScript of any kind. Go on, OmniWeb users, change your user agent string and see if it makes a difference. No, it’s much simpler than that. I have discovered the ultimate technique for hiding specific CSS from OmniWeb – the CSS it can’t cope with – and I’m presenting the trick for you today. I’m going to suggest you call it “CodeBitch’s OmniWeb hack,” or, if your site is G-rated, “CB’s OmniWeb hack.”

Hiding CSS from buggy browsers has a long and distinguished history in standards-based Web authoring. Netscape 4 is the usual subject and so we’ve all had to become familiar with tricks like @import-ing the complex styles that Netscape 4 can’t cope with, or using the media="all" attribute in the link element to hide a linked stylesheet from that browser, among others. There is also a comment-based hack discovered by Caio Chassot that is more precisely focused on hiding CSS from Netscape 4.

There are other ways of referencing styles that OmniWeb doesn’t support – the @media syntax, for example. Until now, however, none of those documented tricks and hacks were suitable for hiding CSS from OmniWeb’s buggy CSS implementation. Every other trick that hid CSS from OmniWeb also hides it from IE5/Mac. This is almost certainly not what you want to do, as IE5/Mac has a very good CSS implementation, especially for CSS1. Indeed, some of the advanced CSS2 selectors used in hiding techniques, like the direct-child, sibling and attribute selectors, are downright disastrous in OmniWeb. You can find out more about what goes wrong by checking out the MacEdition Guide to CSS Support in Mac-only Browsers.

Simple but effective

Here’s the technique. First, call the stylesheet that OmniWeb can handle using a normal link element syntax, making sure you include a media attribute like media="screen" or media="all".

<link rel="Stylesheet" rev="Stylesheet" href="owcanseethis.css" type="text/css" media="screen">

Then call the stylesheet with the CSS that OmniWeb can’t cope with, but use a media attribute with a value that has an initial capital, like this:

<link rel="Stylesheet" rev="Stylesheet" href="owcannotseethis.css" type="text/css" media="Screen">

All CSS-supporting browsers that I’ve tested other than OmniWeb see both stylesheets, so if there’s a style that you want to use for OmniWeb only, not other browsers, you need to override it exactly in the second stylesheet, matching the selector and property exactly, or using a more specific selector. For example, suppose you have styled headings in the sidebar of your page to have gray dotted bottom borders. OmniWeb doesn’t support dotted borders, so you might decide to use a solid border for it instead. So in the first stylesheet you would use the OmniWeb-specific style, #sidebar h3 {border-bottom: 1px solid #999;}, while the second stylesheet would include the style #sidebar h3 {border-bottom:1px dotted #999;}.

Using a combination of the cascade and the two stylesheets, you can hide styles from OmniWeb completely, or pass it styles that only it uses. You can see a simple example in this test page. This CSS-hiding hack is one of the “purest” that I’ve ever seen. We’ve tested widely, and as far as we can tell, it only affects OmniWeb. It’s completely valid HTML, although the CSS validator at the W3C does complain about the capital letters in the media types (probably incorrectly, as I’ll explain below).

The hows, whys and wherefores

It’s such a remarkably simple hack that I’m surprised that nobody mentioned it before. It’s doubly surprising since the initial capital in the media attribute is the way BBEdit inserts it by default (that’s how I discovered it). Maybe people who previously noticed it didn’t think to publicise it. More likely, OmniWeb just isn’t on the radars of standards-oriented Web authors. Everyone knows that OmniWeb’s CSS support is limited, and ignores it.

The reason why this hack works is also a bit surprising. OmniWeb is, of course, treating the media attribute values as case-sensitive, and not recognising values with capital letters in them. There is a reason for this: it appears that OmniWeb is the only browser taking a specified option in HTML spec. The relevant part of the spec reads “A case-sensitive match is then made with the set of media types defined above. User agents may ignore entries that don’t match." But if you go to the CSS spec, it flatly contradicts the HTML spec: “Media type names are case-insensitive.” (This is why it’s funny that the CSS validator complains about the capital letters but the HTML validator doesn’t.) At some point, the W3C managed to write slightly contradictory specifications. It’s a reminder that the standards themselves aren’t perfect any more than the browsers are. But as I’ve argued before, it’s better to have imperfect standards than no standards at all. I hope they will rectify this soon, in favour of the CSS spec.

I’m not the first person to notice the inconsistency, and the view seems to be that case-insensitivity is the way to go here. Indeed, there is some suggestion that it’s simply a typographical error in the spec, given that the text links to the explanation for case-insensitivity. Another possible interpretation is that both behaviours are correct. As W3C staffer Dave Raggett emphasised during the drafting process for the HTML spec, browsers may ignore media types that don’t match a case-sensitive search, but they don’t have to. A brief Google search shows that the tutorial sites disagree on this point: some say it’s insensitive, while others say it’s case-sensitive.

From a practical point of view, case-insensitivity makes more sense. CSS doesn’t only apply to HTML and XHTML, it can apply to other markup languages. So at some level, the CSS spec is more general than the HTML spec. Also, media types enter into @import statements, covered by the CSS spec, as well as the link element covered by the HTML spec. It would be stupid to have these two contexts for media types treated differently, so the CSS spec’s interpretation should stand.

What the Omni Group must not do

Since this isn’t, strictly speaking, a bug in OmniWeb, the Omni Group shouldn’t feel obliged to fix it. In fact, I’m going to call on it to never, ever fix this bug. Not now. Not in Version 5.0. Not even if CodeBitch says it’s okay to fix it. There will always be some bugs we need to work around.

Let’s face it, OmniWeb has some pretty egregious CSS bugs and misimplementations, and I have little confidence that Version 5.0 will fix all of these problems (although many of them should be fixed, or I’ll be even more disappointed in the Omni Group than I am now). Web authors who have significant proportions of OS X users in their audience might want to work around these bugs. This hack allows them to do so. The Omni Group should continue to allow this consideration of its own users. Long live the “CodeBitch OmniWeb Hack”!

— CodeBitch (codebitch@macedition.com) is the grumpy cow who does the HTML production for MacEdition. Read other articles by CodeBitch

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