Here’s the basic markup

<li>
<video>...</video>
<p>...</p>
</li>

I wanted the paragraph to appear when the video is selected. So here’s the simple CSS

section#videolist li {
	position:relative;
}
section#videolist li p {
	display:none;
	position:absolute;
	bottom:-100px;
	left:0;
}
section#videolist li video:focus+p {
	display:block;
}

The sibling selector (+) is telling the browser to display the paragraph as block when its video brother has focus. This is a rough test. There could be some accessibility issues and I’ll need to test this out. Obviously this will not work in Internet Explorer.

However, there are times when your UED provides a design that lacks visual hooks for your screen reader users. A good example may be the ever-popular search form. Most sites will have an input and a button that says “search”. The label for this input is nowhere to be found.

The average sighted user can figure out such a simple form but the screen reader needs a bit more help. Here’s a sound clip of a screen reader trying to use the search form on Yahoo! Kids (.mp3). This was further complicated by the missing alt attribute on the image-based submit button.

I’ve also had to work with table based forms that need some assistance. The table is marked up with appropriate table headers and scopes, but the individual inputs lack labels due to the UED.

The simple solution

There are many ways to hide content via CSS. You want to avoid visibility:hidden and display:none. These will also hide it from the screen reader. You could use text-indent:-1000 em. I prefer using position:absolute; top:0; left:-1000em;. This hides the label by pushing it off screen yet the screen reader is still able to use it.

Updated CSS (updated 4/24/2008)

Adding a top position to your hidden may cause the page to jump when the item is focused. Only use a negative left position and leave the top position out of the equation.

Samples

Let’s look at the complicated table with hidden inputs. The table is properly coded with summary and scope. However, the table would still be difficult for a screen reader without form labels.

Here’s a sample of the HTML code:

Here’s the CSS for the labels


.srinfo {position:absolute; top:0; left:-1000em;}


Extending the hidden screen reader concept

I’ve written earlier about how Yahoo! Tech used a hidden collection of links to replicate an inaccessible flash movie. In a nutshell: screen readers cannot see a flash movie that has wmode:transparent. To get around this, we duplicated the flash content and moved it off-screen for screen readers and search engines.

You could also use this technique for providing information specific to screen reader users, such as:

Hold the Presses, this isn’t perfect!

You can’t just throw anything off screen for the screen readers. The earlier Yahoo Tech example took about made 6 links invisible yet they were still accessible to keyboard users. So, remember, when you use the srinfo class to hide content for screen readers, keep in mind the impact on keyboard users.

Product ratings are represented with 1 to 5 stars. Other sites have used inline images; repeating a solid or empty version for each of the five stars. Other sites, such as Yahoo! Shopping, have used a single inline image representing the number of stars.  At best, the image will have an alt attribute that descibes the number of stars. However, the content is locked inside the image. This is an easy approach for coding but isn’t the most accessible approach.

Yahoo! Tech uses the content first approach to design

Content-first design improves accessibility. This approach places the relevant content in semantic markup. It then uses CSS to transform that content into the visual design. Here is a sample rating from Yahoo! Tech: Overall:4/5, Quality:5/5, Support: 3/5. Our CSS transform that simple text into a series of stars and accompanying text. User testing with a screen-reader user led us to remove visual descriptions from the content, i.e."stars" or "bars".

With the content in the page, it was time to look at the visual design.

Ratings are presented in either an unordered list or definition list. We need to place descriptive text in front of the stars and want the stars to be aligned with each other. These considerations lead to using spans with a combination of CSS rules to hide the text, insert a background image, and absolutely position the ratings to the right side of the list item. Let’s look at the code.

The HTML – span

To use a background image for the stars, we need a container that can be manipulated with CSS and not include presentational behaviors of its own. This is why we use the span, a generic inline container. We could use a strong or em, but feel the span offers the best versatility. You never know when the graphic designer will ask for some text to be bolded or emphasized in the same list item.

Sample code for a rating

The span’s title will generate a tooltip when the user places their mouse over the rating (not Internet Explorer). Screen readers’ default settings ignore title attributes on non-form items.

The CSS

Spans are inline elements.  To display background images, we need to make them display block, define a height, width, and move the text off the screen. To keep them inline with the text, we are also positioning them absolutely. We could position them relatively or floated the spans. Position absolute works the best for our pages.The parent list item is positioned relatively to give the span a contextual anchor. Negative text-indent will hide the rating text.


.ratingslist {list-style-type:none;}
.ratingslist li {position:relative; padding:3px 5px; }
.ratingslist li span {text-indent:-1000em; width:66px; display:block; position:absolute; top:5px; right:20px;}


Image sprites display the desired number of stars

The list item is given a class with a number at the end (stars8). This will display an image with four out of five red stars. We are using a scale of 0 to 10 to accomodate half stars. To display other rating variations, we change the modifier, i.e. prostars4, retstars4, bars4, bigstars4, etc…

To simplify the maintenance of the site and reduce server requests; Yahoo! Tech also uses image sprites. Sprites are single images that include multiple icons with a consistent spacing between them. Use background positioning to display the desired chunk of the image. Each sprite represents the possible color variations used on the site: red, blue, and green. Minimizing the color palettes reduces the final image size. For more information on sprites, read CSS Sprites: Image Slicing’s Kiss of Death by Dave Shea. As a further enhancement, alpha transparent png images are used for most browsers and index-transparent gifs are presented in the Internet Explorer 6 style sheets. 

Background images are positioned with the set of numbers after "no repeat." The horizontal positioning is first. Our sprite is vertical, so we are leaving it alone, hence the 0 value. The vertical positiong comes next. If we want to display 2 out of 5 stars, we need to shift the background down to that part of the image (-530px). Here is the CSS for presenting the specific star variant.


/* Ratings images
======================================= */
.stars0 span {background:url(/images/bg-ratings.png) no-repeat 0 -650px;}
.stars1 span {background:url(/images/bg-ratings.png) no-repeat 0 -620px;}
.stars2 span {background:url(/images/bg-ratings.png) no-repeat 0 -590px;}
.stars3 span {background:url(/images/bg-ratings.png) no-repeat 0 -560px;}
.stars4 span {background:url(/images/bg-ratings.png) no-repeat 0 -530px;}
.stars5 span {background:url(/images/bg-ratings.png) no-repeat 0 -500px;}
… (repeated for each variation of the stars and bars)


This approach has allowed the Yahoo! Tech engineers to maintain a consistent presentation with minimal markup. For pages that need special tweaks we can easily adjust the positioning by using descending selectors:


#mytech .ratingslist li span { right:5px;}


Caveats

We’ve only found a few small issues with this approach.

• You cannot count on background images being displayed on the printed page. Our print style sheet removes the text-indent and background images to display “Overall: 4/5”.
• When someone includes more than 4 products in the comparison table, the text of some rating parameters will begin to overlap the stars. If they were inline images or if we floated the spans, they may drop to the next line.

Yahoo Tech! ratings are another example of creating accessible and visually dynamic pages by considering the underlying content structure before attacking the styles. Users of all abilities are presented with solid information. That’s how you can deliver a 5 star page every time.

Related Information

• CSS Sprites: Image Slicing’s Kiss of Death by Dave Shea.
• Making Flash Accessible to Screen Readers
• Standardista Search: Sprites

Take a look at the list and think of it as new tools to use.

Bugs we fixed

All bugs on positioniseverything.net except the “escaping floats” bug (which is planned for the future)

• Peekaboo Bug
• Internet Explorer and Expanding Box Problem
• Quirky Percentages
• Line-height bug
• Border Chaos
• Disappearing List-Background bug
• Guillotine Bug
• Unscrollable Content bug
• Duplicate Characters Bug
• IE and Italics
• Doubled Float-Margin bug
• Duplicate Indent bug
• Three pixel text jog
• Creeping Text bug
• Missing First letter bug
• Phantom box bug

Details on some of the other bugs (from sources other than the positioniseverything.net list) that we fixed:

• Overflow now works correctly! (That means boxes do not automatically grow any more.)
• Parser bugs: * html, _property and /**/ comment bug
• Select control: CSS style-able and not always on top
• Auto-sizing of absolute positioned element with width:auto and right & left (great for 3 column layouts)
• Addressed many relative positioning issues
• Addressed many absolute positioned issues
• % calculations for height/width for abs positioned elements http://channel9.msdn.com/ShowPost.aspx?PostID=191182
• <?xml> prolog no longer causes quirks mode
• HTML element truly independent of the Body (now gets its own width, height etc.)
• 1 px dotted borders no longer render as dashed
• Bottom margin bug on hover does not collapse margins
• Several negative margin issues fixed
• Recalc issues including relative positioning and/or negative margins are fixed now
• CLSID attribute of <object> tag no longer limited to 128 characters
• :first-letter whitespace bug described in http://blogs.msdn.com/ie/archive/2005/09/02/460115.aspx fixed
• Descendant selector now works properly for grand children when combined with other selectors
• First-line and first-letter now applies when there is no space between word :first-line and opening brace {
• Pseudo-classes now are working as expected if selector is excluded
• The :link selector works now for anchor tag with href set to bookmark
• Addressed !important issues
• PositionIsEverything piefecta-rigid.htm now works
• List-item whitespace bug fixed
• Fixed Absolutely Buggy II
• Absolute positioned elements now use always correct containing block for positioning and size information
• Nested block elements now respect all overflow declarations (hidden, scroll, etc)
• Fixed the opposing offset problem (absolute positioned element whit all four top, bottom left and right are present)
• <a> tags nested within LI elements will no longer add extra bottom margin when hover occurs
• We no longer lose the image aspect ratio on refresh
• Cleaned up our ident parsing according to CSS2.1 rules
• Fixed parsing bugs for multi- class selectors and class selectors that are combined with id selectors
• And many more

We also extended our existing implementations to comply with W3C specifications:

• Enable :hover on all elements not just on <a>
• Background-attachment: fixed works on all elements – so Eric Meyer’s complexspiral demo works
• Improved <object> fallback

Finally, we added new features from CSS2.1:

• Min/max width/height support (also for images, which did not work in IE7b2)
• Transparent borders
• Fixed positioning support
• Selectors: first-child, adjacent, attribute, child
  • A couple of CSS 3 attribute selectors: prefix, suffix and substring since we were working already in the code base (also the general sibling selector)
• Alpha channel PNG support (Not a CSS feature but too important for designers to not call it out J)

IE Blog

IE7 is still not as good as Firefox, Opera, or Safari. However, Microsoft is planning an aggressive updating campaign and hopefully it won’t be long before we can count on our average user’s browser supporting advanced CSS styles. It’s time to stop complaining about IE6 and begin planning how you will use these new tools.

Internet Explorer 7beta2 is not treating transparent png background images correctly. It sees “background-position: 0 0″ as “background-position: 0 100%”. Come to think of it, I have only tried a vertical sprite, this may be the same for a horizontal sprite.

What’s the solution?

You could create a series of rules in your IE7 style sheet to measure your new sprites from the bottom up, instead of top down. But this doesn’t solve some of the other odd issues with IE7 and transparent png images. I’ve seen the images load upside down and I’ve seen the images move when you scroll the page and the image hits the bottom of the browser. I thought I was going crazy or that I had some sort of mutated version. But this pseudo-animation works on other computers.

Our IE6 style sheet replaces our pretty alpha transparent png graphics with a simpler index transparent gif version. We replaced our re-measured rules in the IE7 with this set and it has solved our problems. It would be great to take advantage of IE7′s ability to use alpha transparent png images, but this bug is just driving me nuts. I’ve also been in contact with the IE7 team. They are dedicated to building the best browser possible within their constraints and hopefully this will be figured out before the final launch of IE7.

One other note of advice. Creating alpha transparent png images via the save as command in Photoshop on a Mac gave us the worst results. Those images did some very funky things on the page. Fireworks created better images.

c’est fini!

I don’t know if it is official or not, but I can say that the Microsoft engineers are interested in what developers have to say and have worked on this bug. I believe it has been fixed and will be all good to go with the final release of IE7. I can’t confirm or deny this, but I am pleased with their response to my initial post and followup.This bug has officially been officially fixed as of Release Candidate 1 and you can use your transparent png sprites without a worry in the world!

Yahoo! Tech’s home page features a flash-based media space that highlights stories, comparisons, buying guides, blog posts, and more. Making this accessible required a bit of trial and error, but the solution was simple and can be used by sites everywhere.

Step 1. Inserting the flash object

The site uses the Unobtrusive Flash Object script by Bobby van der Sluis. This script checks to see if the user has JavaScript enabled and the correct version of Flash in their browser. If so, it inserts the code required to display the movie. If the user doesn’t have the requirements, a default set of information is presented.

This script cures the validation errors caused by the normal flash insertion code. Theoretically, it would also allow you to provide good, accessible content to those not using JavaScript and Flash enabled browsers, i.e. screen readers and search robots.

Window Mode Transparency conflict

However, we had an issue with the flash movie conflicting with a DHTML drop down menu. The flash movie wanted to have the highest z-index and thus sat on top of the menu. To cure this problem, we added the attribute wmode:transparent. This tells the flash movie: your window mode is transparent, you are not the boss, go sit in the back and let others take center stage.

This cured the overlapping issues but negated the accessibility features that we had hoped for. User testing with a screen reader was disheartening. Screen readers ignore flash movies with window mode transparent. They want to do what’s best for the user and ignore the little guy in the back corner.

We began searching for answers on the flash and accessibility forums and couldn’t find a way to get screen readers to read a flash movie with wmode:transparent. It simply isn’t possible at this time.

Step 2. Time for a detour

The U.F.O. enabled page features a div with default text. This is where we originally duplicated the content being fed via xml to the flash movie. Our hope was that the screen readers would ignore the flash and read the HTML content in this div. When this wasn’t possible, we literally thought outside the box.

The U.F.O. script uses visibility:hidden to hide the default box. We tried using text-indent and negative margins instead, but it still was not available to the screen reader.

The default div now has your standard non-optimized warning text: “For the best experience, please enable JavasScript and download the latest version of Flash….”

We then created a new div (id=”alternatecontent”) that features the content from the flash movie. It is pushed off screen by using absolute positioning. This hides the duplicated content from the visual design while providing the content to those without the visual abilities.

We’re satisfying two audiences with just a little extra code. Add the extra div for your screen reader audience (…and search engines!) when using wmode:transparent in your Flash movie. You’ll create valid, visually dynamic, and accessible pages.

Listen to the Yahoo! Tech media space as read by a screen reader (.mp3)

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I use sprites extensively. I love the way they save server requests and I think they are much easier to maintain. The thought of fixing all of my sprites was enough to send me downstairs for another coffee. But I noticed the only sprites being affected were the ratings. I needed to find what was special about these. The ratings sprites use a span that is absolutely positioned in either an unordered list or definition list. This gives us flexibility for displaying them across the site.

IE7 Does it Right!

I created a test page for using sprites. I stripped the CSS down to simple list handling, floating, positioning, and sprite. IE7 handled it perfectly. I even replaced the links with spans and that still didn’t trip up IE7. Take a look at the test page , IE7 Sprite Test, to see the results. While I’m still having problems with IE7′s handling of sprites. I believe it is a unique combination of styles that is causing this issue. I don’t think the average person will need to worry about this.

When I do figure out what is going on with Yahoo! Tech’s rating sprites, I’ll update this blog with the solution. For more information on using sprites, visit Dave Shea’s article CSS Sprites: Image Slicing’s Kiss of Death on A List Apart.

The Breakdown

The site has a series of floated divs to display the screenshots. The screenshot is applied as the background image of the div with an inline style. Inside the div is a link that is given display:block and a transparent background image.

Great idea – room for improvement?

While I think the visual design for these screenshots is well thought-out. I don’t like the underlying code. The screenshots are content; miniature representations of other sites. Adding them to the CSS is treating them as decorative elements. The text for each link is: “SCREENSHOT, ” making the page unusable with the styles disabled. To give this page more structure and semantic strength, I would modify the underlying code as such:

HTML Code

CSS Code


.screenshotlist {float:left; list-style-type:none;}
.screenshotlist li {float:left; margin:9px; }
.screenshotlist a {display:block; width:146px; height:130px; position:relative; }
.screenshotlist a strong {text-indent:-1000em; z-index:20; position: absolute; top:0; left:0; width:100%; height:100%; background:url(screenshot.png) no-repeat -154px 0; }
.screenshotlist a:visited strong {background-position:0 0;}
.screenshotlist a img {margin:5px 0 0 5px; border:none; z-index:1;}


Benefits of the new code

The screenshots now have some structure; an unordered list with links full of good, crunchy content. Screenreaders and those without CSS will have access to the information. Javascript can be used to target links within the screenshotthumb div to open a new window without the need of inline scripting.

Cavaets: I haven’t tested this code yet. It’s very possible the z-index styles are not required. As an alternative, remove the margin on the image and replace it with a border. Add a rule to change the border color on hover and visited.

Design Meltdown is a great site for learning about design concepts. I’ve gleaned a number of nice ideas from them and would love to say I gave a bit of help back to them.

The Setup

You have a page that terminates in a sturdy footer, such as this site. You’d like the footer to be cemented to the bottom of the browser window regardless of the amount of content. How do you position the footer at the bottom on a small page, yet not cause a conflict with long page? It’s actually more irksome than you would imagine.

The Solution

The footer is placed outside the content wrapping div. The html, body, and content div are given height:100%, which pushes the footer off screen. The footer then uses negative margins to sneak back up into the page. For pages with longer content, space is needed in the content div to avoid overlapping on the bottom.

Based off the original footerStick, footerStickAlt sets up the Web page so that it will span the entire height of the browser window, even if the content is less than the height of the browser window. However, where footerStick then used absolute “bottom” positioning to get the footer to appear at the bottom of the screen/content, footerStickAlt positions the footer outside the height of the content, and then applies a negative margin to get it to display inside the browser window.

So, where footerStick’s code requires you to place the footer inside a containing element, footerStickAlt requires you to place it outside the element:

You then need to apply a bit of CSS:


html { height: 100%;}
body { height: 100%;}
#nonFooter { position: relative; min-height: 100%;}
* html #nonFooter { height: 100%;}
#Footer { position: relative; margin-top: -7.5em; }


…For the case where the Web page content is larger than the browser window, the footer will be positioned naturally below the content, then brought up by the margin. For this scenario you should provide a bit of space at the bottom of your content which the footer can rise into without covering anything. This can be done with a bit of padding or margin on your content.

The only drawback to footerStickAlt is that you must know the exact height of your footer (whether it be in absolute or relative pixels). However, you have to know this roughly with the original version anyway, in order to make room for the footer at the bottom of the content. It’s generally a non-issue with footers anyway, as they have limited information and a sparse layout.

Cameron Adams – footerStickAlt

I have a topnav consisting of an unordered list with a dropdown menu on one of the list elements. The dropdown is a nested unordered list with position:absolute and a z-index to sit on top of any page content below. Fairly simple so far…

However, in IE6, the menu is obscured by an h5, random images, and paragraphs on various pages. The z-index should make this list float on top of other elements, but it seems to be ineffective.

PPK summarized this problem on his post: Explorer z-index bug:

It appears that in Internet Explorer (windows) positioned elements do generate a new stacking context, starting with a z-index value of 0, causing the lime-green box to appear above the yellow box.

This is a serious violation of the CSS specifications, causing headaches and a lot of misunderstanding of what z-index really does.PPK

While crediting Aleksandar Vacić for first reporting this bug, PPK doesn’t mention Aleksandar’s simple solution. Give the parent a position:relative and z-index:1..

Now, of course it isn’t always that simple. There’s also the issue of subsequent objects that also have a z-index and what happens if their parent is also positioned with a z-index. Please take some time to visit Aleksandar’s web site if you are having this conflict.

IE7 and more fun

According to PPK’s web site, this has not been fixed in IE7 Beta2Preview. We’ll see how this works out. I’ve noticed some positioning bugs in IE7 myself. This is something to consider when considering the z-index happiness of Andy Clarke

More solutions

Hedger Wang has an ingenious solution to the conflict between z-index on elements and subsequent select elements. He uses an iframe with z-index-1 that sits under the targeted element. I’ve used this negative z-index on some of the subsequent elements and it is helping. Fixing all of the pages will be a long journey , but at least there is light at the end of the tunnel.

Yet another hack/update

I had to remove the negative z-index from the container as it was keeping a link with background image/text-indent, display:block, etc from having any hover activity. It acted as if it were under a layer. Other links in the container were fine. You’ve got to love IE6

Yet another hack/update 4-30-06

We were using an iframe with the src=”/”. Can you guess what happened? Oh my goodness. We were loading the home page inside every other page on IE. So here’s the tip we learned… don’t use a page url for your invisible iframe, use an spacer.gif or something benign instead. Better yet, get rid of the iframe if you find other solutions. Which is what we ended up doing. We’ve messed with this thing for so long we’ve lost track of what’s doing what.

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