The video was very good but in the beginning Misko Hevery struggled a bit to describe it and at the end admitted the biggest problem was explaining to people what <angular/> is. To me it is clearly a language, and an extensible one at that. It is (or at least contains) as he describes an HTML compiler. Doesn’t a compiler imply some language to compile. The source is clearly more than just HTML so it must be more than just an HTML compiler. I wonder if there is some reason he avoids calling it a language. The fact that it can be extended to handle new behaviors, widgets, etc. just makes it a better language. Is there some fear that calling it a language would put people off? It doesn’t bother me since I previously said that higher level languages will provide the biggest productivity gains.

The parallels I was talking about are:

• Its a declarative language
• The language is designed to be extended
• It has two way data binding

Two way data binding is a very important aspect in simplifying the creation of web apps. The first time I ever saw data binding was back in the the late ’80s. I was visiting a friend that was working on a maser, which is cool (literally) in its own right, but what caught my eye, as he showed me around his lab, was some software running on an old Mac. That software was LabView. The fact that a line drawn between a sensor and a gauge meant that any time the senor value changed the gauge was updated really impressed me. More recently I noticed that data binding is built in to the JavaFX language. I haven’t written any programs in LabView or JavaFX so I’m not sure if the bindings can be bidirectional but I’m pretty sure at least in JavaFX that bidirectional changes can be accomplished.

It is the two way data bindings that most notably distinguish <angular/> from template languages. I used to be a big fan of template languages, and StringTemplate was my favorite. Lately I have found them to be less useful. One reason is that in my recent work I have found that procedural logic far outweighs the amount of template text. The bigger reason is that most template languages don’t automatically protect you from script injection (XSS). There are many JavaScript template languages available now and I don’t have a need for any of them. But <angular/> is different — it is not a template language and it looks like it protects against script injection by default.

<angular/> is new but it looks very promising.

• Performance. One of the performance recommendations made by Yahoo’s performance team is to reduce HTTP requests. One way to do this is using the CSS Sprite technique — combining many images into a single background image.
• Skin-ability. With the img tag the image URL is in HTML markup where it is hard to change. With CSS Sprites the image URL is in a CSS file making it more convenient to change. Sure you can change the contents of the original file but there are reasons for changing the URL. It is not as easy to move the images to a different server or group them in different image files when the URL is not in CSS.

However there are drawbacks. The biggest is accessibility, specifically high contrast mode. In high contrast mode all background images and colors are ignored — replaced with high contrast colors such as white on black or black on white. The other issue is that background images are not always printed.

The prevailing accessibility advice is to not use background images for functional images. The underlying problem is that there is no way in HTML/CSS to identify a background image as being functional. They are all considered decorative. It is also true that not all img tag images are functional but again there is no way to distinguish them for the purpose of high contrast mode. So high contrast mode makes a reasonable assumption that background images are decoration to be removed and img images are functional and must be shown. From here on I’ll call functional images icons. They either convey important information or are interactive (like a toolbar button for example).

I have seen recommendations that functional background images should be replaced with text when high contrast mode is detected. This does not seem right to me at all. A desktop app does not change its toolbar button icons to text in high contrast mode. The assumption is that icons are already designed to have reasonable contrast.

It also just feels right to me that the icon URLs should come from CSS.

Since I care about performance and accessibility I’m not happy with this conflict. I want a solution that puts the icon URL in CSS, works in high contrast mode and allows me to combine icons into a single image file. Here is what I came up with.

My typical markup for an icon is something like this:

    <button><span class="icon edit"></span></button>
    <button><span class="icon delete"></span></button>

The basic style is:

span.icon {
    display: -moz-inline-box;
    display: inline-block;
    width: 16px;
    height: 16px;
}
button span.icon.edit {
    background: transparent url(images/toolbar.png) no-repeat 0px -32px;
}
button span.icon.delete {
    background: transparent url(images/toolbar.png) no-repeat 0px -16px;
}

This creates a button with an edit icon assuming that toolbar.png is a sprite image with the edit icon at offset 0, 32 etc. I left out extras like a title tooltip and hover and active states for the button icon to keep things simple. This works nicely until high contrast mode is turned on.

You can use the same sprite image in an img element and position it relative to a fixed size parent that has overflow:hidden to achieve similar functionality to a background image.

For example:

    <button><span class="icon edit"><img alt="" src="images/toolbar.png"></span></button>
    ...

The style to make this work is:

span.icon {
    display: -moz-inline-box;
    display: inline-block;
    width: 16px;
    height: 16px;
    overflow: hidden;
    position: relative;
}
button span.icon.edit img {
    position: relative;
    left: 0px;
    top: -32px;
}
...

This works in high contrast mode (as well as normal mode) and has multiple icons in a single image but the image URL is in the markup not in the stylesheet. What I want to do is use JavaScript to take the image URL from CSS and dynamically add the img element as a child of the icon span. The html mark up and stylesheet will be the same as the first example above except that the stylesheet will have these additional styles:

span.icon.edit img {
    top: -32px;
    left: 0px;
}
span.icon.delete img {
    top: -16px;
    left: 0px;
}

These additional rules are not too much extra work considering you will usually have additional rules to adjust the position on hover and active states anyway.

My first attempt tried to get the URL from the current styles using jQuery like so: $(…).css(“background-image”). The trouble is that in high contrast mode the effective current background image is “none” even though the CSS file does have a background image. This makes sense — the program should “see” what the user sees. The solution is to get the actual background image directly from the CSS rules. This takes a little fiddling to get it to work cross browser. Some browsers return the full URL and some return exactly what is in the CSS file. Some times its wrapped in quotes.

This test page shows an example of the traditional CSS Sprite technique as well as my jQuery enhanced high contrast mode compatible version. All the styles and JavaScript are in the html file to make it easy to see how it works. It also contains code to detect high contrast mode. One option is to only make the dynamic change if high contrast mode is detected but that is not the approach I took in the test page.

View the page with high contrast mode turned on and off to see the difference. Note: not all browsers or operating systems support high contrast mode. Firefox and IE on Windows do. It is also important that the dynamic changes work even in browsers that don’t support it (by work I mean that the icons look right and are functional, not that high contrast mode magically starts working in browsers that don’t support it). I tested on Windows with IE8, FF3.5, Safari 3.2 and 4.0, Opera 10 and Chrome and found that they all worked. I also tested on Linux with FF3 and found no problems. I don’t have a Mac to test with. I tested with IE6 and found that it did not work. More investigation is needed but IE6 is not a high priority for me right now. I need to test with IE7 but don’t have it handy right now.

Feedback on how it works in other browsers and operating systems would be very helpful.

I did not do any performance testing. The assumption is that moving the image from the background to an img tag will not cause the image to be requested from the server. The Firebug Net tab indicates that it is fetched just once. The page seems to render fast enough with no flashing. More testing is needed but I think the principal is sound. The script could use some improvement to be more robust especially for much older browsers so they at least fall back to using the CSS sprites as is. I bet there are other cases of relative URLs to test for as well.

Keep in mind that the test page is meant to demonstrate just this technique. It has a bunch of other accessibility no-nos such as the disclose icons are not focusable, keyboard accessible, and have no screen reader accessible label text.

When you use the focus method to set focus to a focusable element the expectation is that, in the absence of css rules to the contrary, the browser will show a focus outline around the element using its default style. This is what happens in Firefox, Chrome, and Safari. (Opera has its own set of focus problems which I didn’t investigate fully.)

There are a number of elements that are naturally focusable, such as inputs and anchors. In addition any element with a tabindex attribute equal to -1 is focusable. If the tabindex is non-negative then it is focusable and in the tab order. My test case uses list elements with tabindex of -1 or 0. I suspect that the same is true of other elements using tabindex.

Older versions of IE (I tested IE6 and I believe IE7 works the same in this regard) had some strange additional requirements beyond just calling focus. The outline would not be shown if the focus method was used to give focus to an element with a tabindex of -1. So before setting focus you would have to set the tabIndex to zero (or a positive number).

elem.tabIndex = 0;
elem.focus();


Also if you click on an element with tabindex of -1 no outline is shown unless the className is updated (even if the value doesn’t change). Perhaps other style changes would work as well.

IE8 adds some new bizarre behavior. First if css is used to set an explicit outline style on the elements (either directly or inherited) then the old IE quirks mentioned above go away as well as the new IE8 problem described below. Setting your own outline style for focus isn’t a good idea unless you are giving your whole web app a focus style makeover. I think it is best to stick with the default styles since it is what the user is probably used to. There is also the problem of old browser like IE6 not supporting the outline style.

If the className of the element receiving focus is updated in the onfocus handler while the tabIndex is -1 then no focus outline is shown. Assuming that the tabIndex is -1 and addClass is a function that adds a class to the className, one would expect the following two lines of code could be executed in either order.

addClass(elem, "myfocus");
elem.tabIndex = 0;


In IE8 setting the tabIndex to zero must be done first or the outline is not shown. This is exactly what tripped me up. If I just happened to write the statements in the opposite order I would never have discovered these oddities.

Note that in all cases focus is actually set correctly it is just the visual indication of focus that is wrong – but thats the important part of focus.

I created a test page that allows playing around with these rules. It is also an example of how focus can be managed with a roving tabindex. If you play with this page in different browsers you will notice that in Firefox (versions 2 – 3.5) , Chrome, and Safari 4 (I tested on Windows) it doesn’t matter what options are checked, the behavior is correct. In IE you can play with the options to see which combinations work.

I wonder if this is intentional in IE8 or is something that will get fixed in a point release.

One nice thing about working at Oracle is that they take accessibility seriously. I have worked on web apps before that were supposed to be accessible but this is the first company I have worked for where I could actually get my hands on a (non-demo-mode) JAWS screen reader to do my own testing. You can try to follow all the best practices but you really do need to test with a screen reader to know how well you have done.

I have found that keyboard accessibility and screen reader accessibility are somewhat at odds.

If you do the right thing for keyboard accessibility (i.e. managing focus) and don’t use WAI-ARIA at all then you have a chance of being accidentally partially accessible in JAWS and probably other screen readers. This is assuming that you follow best practices for being accessible to screen readers (use label correctly, use native form controls – links, checkboxes etc. in semantically appropriate ways).

The problem is that all your keyboard/focus management logic is in vain since you are probably going to use arrow keys and JAWS is not going to give them to you (JAWS uses many keys for itself). The reason you have any chance of success is because the normal screen reading behavior of the arrow keys may be close enough and using native form controls will allow JAWS to access them in a reasonable way. How well it works will depend on the details of your rich control. The best you can do is to try to find the right balance between normal use and screen reader use. This should work OK with older browsers and screen readers depending on the various bugs and odd interactions between various browser and screen readers.

The other option is to go the full WIA-ARIA route. By using the appropriate ARIA roles and states and properties you can get JAWS version 10 (and presumably other new ARIA aware readers) to give you the keyboard keys you need. For this to work you need very recent versions of browser and JAWS. I have had some initial success with JAWS 10 and FF3.5. It looks like this approach will provide the very best functionality for all users. I have not yet tried the combination of JAWS 10 and IE8. The trouble is that the combination of JAWS 10 and IE7 works quite badly when you use ARIA. JAWS seems to get some of the ARIA information like roles but doesn’t get enough to work correctly. It gives up the keyboard keys but then doesn’t handle the ARIA based changes and therefore the normal JAWS arrow key functionality doesn’t work either. This is the worst possible behavior. Presumably older versions of JAWS that don’t know anything about ARIA will work fine with IE7 even if the rich control uses ARIA provided the ARIA support is on top of non-ARIA techniques mentioned previously. I have not yet tested this combination.

To me this means that if you are adding on to an existing app that must support older browsers or screen readers then using ARIA probably isn’t worth it yet. But if you are starting a new app that wont be released for a while then using ARIA is the way to go. You can still support older browsers but you would have to require that for screen reader accessibility an ARIA aware browser and reader must be used.

Another possible solution is to have an option to turn WAI-ARIA support on or off. I don’t like this because of the added complexity of implementation and testing.

Here are some resources that I found very useful in my recent accessibility work: Improving Accessibility Through Focus Management, WAI-ARIA Best Practices, and Delegating the focus and blur events.

I recommend reading “Language Oriented Programming” by M. P. Ward. It also claims programmer productivity as a benefit of what it calls the “middle-out” development style.