Accessibility: HTML Keyboard Shortcuts with "accesskey"

Accessibility is a hot topic on the web, and there are many emerging standards to help move in an accessible direction. We have CSS media types, alternative web pages with simpler navigation and high-contrast styling, alt and title tags, and the general move away from mixing style with substance.

Along with all of this, we have the relatively old standard of using the accesskey attribute on invokeable elements such as hyperlinks and form inputs. This allows us to attach a keyboard shortcut to elements in our webpage.

Unfortunately, this isn’t a widely used, or easily implemented standard. Although the accesskey attribute is widely supported, only one commonly-used browser (Opera) at the time of writing provides an easy way for users to see what accesskeys are enabled on a given site, and there is no widely-accepted standard for choosing which accesskeys perform which function.

However, with a little jiggery-pokery we can implement a simple way to show accesskeys on demand:

This link will bring you to this post’s permalink, and can be actuated with the accesskey “9”; in Firefox, you hold alt-shift and press 9.

The code for the above is pretty simple. First, the button:

The hyperlink itself (abbreviated):

<a href="https://jeremysmyth.com/...." title="Link to this post">This link</a>
will bring you...

Finally, the javascript:

function showKeys() {
	if (document.styleSheets) {
		var sheet = document.styleSheets[0];
		var len = sheet.cssRules.length;
                // reformatted to fit
		sheet.insertRule("[accesskey]:after {" +
                        "font-weight: 700; " +
                        "border-bottom: 1px blue dotted; " +
                        "content: '[' attr(accesskey) ']';}" , len);
	}
}

Clicking on the button calls the “showKeys()” function in the Javascript script block, which adds a style to the current stylesheet. The style automatically styles elements with the “accesskey” attribute, adding the value of that attribute after the element itself.

Put simply, it adds a styled [9] after the hyperlink, because (1) it has the “accesskey” attribute, and secondly, the “9” is the value of that attribute, as calculated by the attr() function.

Note: The above Javascript won’t currently work in Internet Explorer; for that, you’d need Microsoft’s addRule function rather than the standards-compliant insertRule I’ve used.

HTML: Title Tooltips and Alt text

Sadly, another one for the Internet Explorer Vs. Firefox debate.

It’s pretty well known that most browsers will display a tooltip of sorts when you hover over an image. The alt attribute of the img tag gives rise to that, in pretty much all places.

Lesser known is the title attribute, which is supposed to give the tooltip; the alt attribute might do that as a side-effect if title isn’t there, but it’s just that: a side-effect. The alt attribute is really there to give browsers that aren’t displaying images (or screenreaders that can’t see them anyway) some idea of what the image is.

This separation of concerns is somewhat of a problem when it comes to image maps: in image maps, the alt text for the area elements is there for similar reasons, to show what options are there when the image isn’t there. The title attribute is there for the tooltip, as ever.

However, if both alt and title are there, Internet Explorer shows the alt text as a tooltip, where Firefox will show the title text. Although they serve very different functions, a conscientious web developer is forced to keep them identical, or risk causing problems for the non-standards-compliant behaviour of Internet Explorer.

Of course, title will still work in other places, for example on images or even links:

<a href="mypage.html" title="My lovely page!">My Page</a>

Delving into the XHTML 1.1 DTD

So, you’re looking at the top of a web page’s source code, and you see something like this:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

What’s the relationship between that and the actual code in the web page?

Well, a DOCTYPE tag declares what document type this webpage is, by formally specifying a Document Type Descriptor (that’s what the “dtd” in the filename and in the declaration means). This is the formal specification, written in its own computer language, used to define legal dialects of languages descended from SGML. Most predominantly, this includes languages like HTML 4.01 and XHTML. Hence this walkthrough.

In our specific case, it references a specification for XHTML, which is a modular XML-expressed version of HTML. Let’s look inside.

Firstly, if we look in the declaration, we see the link ““http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd” which, if you download it, shows the DTD itself. For XHTML, this is a relatively short document; the specification largely consists of modules, referenced from this document. Let’s have a look.

Within the DTD, you’ll see this section (around line 121):

<!-- Text Module (Required)  ..................................... -->

&lt;![%xhtml-text.module;[

%xhtml-text.mod;]]&gt;

This defines a module to be included, which itself is a technically part of the DTD as it is INCLUDEd.

If you navigate to the included module, “http://www.w3.org/TR/xhtml-modularization/DTD/xhtml-text-1.mod”, you’ll see a further set of INCLUDEd items, for example:


&lt;![%xhtml-inlstruct.module;[

%xhtml-inlstruct.mod;]]&gt;

This entry includes the inline structural elements br and span, and further down the document we have more included modules containing inline phrasal elements (em, strong etc.), block structural (p and div), and block phrasal (h1, h2 etc.).

Try them:

In each, you’ll see the definitions for tags such as p, div, code, strong, em and so on.

For comparison, have a look at the HTML 4.01 DTD, which you’ll be able to follow using the DOCTYPE:

…and linked to from here: http://www.w3.org/TR/html4/strict.dtd. As you’ll see, it’s not quite modular, but still contains code defining the elements (and their contents, attributes and so on) that are legal within the dialect concerned.